Weatherford Sand Control Manual A4 R1

GENERAL INFORMATION ON

Weatherford Sand Control Systems External Manual Rev 1.0 June 2001

For further information, contact your nearest Weatherford Completion Systems location or the addresses below. A list of locations can be found on the world wide web at http://www.weatherford.com/locations/index.asp. The home page is located at http://www.weatherford.com.

Americas

Europe/Africa

Asia/Pacific

Weatherford Completion Systems 515 Post Oak Blvd. Suite 600 Houston Texas 77027 Tel: 713 693 4000 Fax: 800 257 3826

Weatherford Completion Systems Weatherford House Lawson Drive, Dyce Aberdeen AB21 0DR Tel: +44 (0)1224 762 800 Fax: +44 (0)1224 771 309

Weatherford Completion Systems Rohas Perkasa th 12 Floor, West Wing 8 Jalan Perak 50450 Kuala Lumpur Malaysia Tel: 603 2168 6000 Fax: 603 2162 2000

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TABLE OF CONTENTS 1.

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8.

Introduction.................................................................................................................................. 1 Scope .......................................................................................................................................... 1 Weatherford Completion Systems Capabilities & Contact Information....................................... 1 Sand Control ............................................................................................................................... 1 Acknowledgements ..................................................................................................................... 1 WCS Sand Control Systems Overview ....................................................................................... 2 Background ................................................................................................................................. 2 Slotted Liners .............................................................................................................................. 3 Wire-Wrapped Screens ............................................................................................................... 4 Pre-Packed Screens ................................................................................................................... 5 Premium Screens........................................................................................................................ 6 Gravel & Fracture Packs ............................................................................................................. 7 Expandable Systems .................................................................................................................. 9 Sand Control Issues .................................................................................................................. 10 Sand Grains .............................................................................................................................. 10 Particle Size Distributions ......................................................................................................... 13 Media Sizing Rules.................................................................................................................... 15 Open Area to Flow .................................................................................................................... 19 Draw-Down................................................................................................................................ 22 Borehole Support ...................................................................................................................... 23 Mud and Drill-in Fluid Conditioning Recommendations ............................................................ 26 Centralisers ............................................................................................................................... 34 Inflow Profile along Horizontal Wells......................................................................................... 35 Erosion Resistance ................................................................................................................... 37 Corrosion Resistance ................................................................................................................ 45 Screen Specifications................................................................................................................ 46 Sand Control System Selection ................................................................................................ 47 Selection Process...................................................................................................................... 49 Risk Management ..................................................................................................................... 56 Weatherford System Advantages ............................................................................................. 57 Wire-Wrap Screen Solutions..................................................................................................... 58 Wire-Wrap Screens ................................................................................................................... 60 ® Houston-Weld Screens............................................................................................................ 61 ® Dura-Grip Screens................................................................................................................... 61 Free-Flow™ Screens ................................................................................................................ 65 Pre-Pack Screens ..................................................................................................................... 66 Zonal Isolation ........................................................................................................................... 71 Pre-pack & Wire-wrap Selection Criteria for Internal Gravel Packs.......................................... 72 Wire-Wrap Screens Safe Application Limits ............................................................................. 73 ® Stratapac Screens ................................................................................................................... 74 Stratapac Construction.............................................................................................................. 75 Screen Pore Size Distribution Technology................................................................................ 83 Screen & Media Selection Guidelines....................................................................................... 85 Comparison Tests ..................................................................................................................... 87 Gravel Pack Issues ................................................................................................................... 95 Horizontal Open-Hole Gravel Packing ...................................................................................... 95 Cased Hole Gravel Packing ...................................................................................................... 97 Gravel Sizing and Screen Selection.......................................................................................... 99 Expandable Sand Screens...................................................................................................... 105 Introduction.............................................................................................................................. 105 ESS Construction .................................................................................................................. 107 Expandable Isolation Sleeve (For Information)....................................................................... 110 Expansion Systems................................................................................................................. 110 ESS Mechanical Properties .................................................................................................... 112 ESS Installation Procedures ................................................................................................... 113

9.

Use of ESS in Combination with Other EST Products............................................................ 119 Accessory Equipment ............................................................................................................. 119 Technical Issues...................................................................................................................... 119 ESS Media Testing.................................................................................................................. 121 Borehole Support .................................................................................................................... 123 Support Services ..................................................................................................................... 133 Technical & Operational Support ............................................................................................ 133 Sand Prediction & Production Technology Support................................................................ 133 Engineering, Manufacturing and Service Support .................................................................. 133

LIST OF FIGURES Figure 1: Slotted liner ............................................................................................................................. 3 Figure 2: Dura-Grip wire-wrap screen .................................................................................................... 4 Figure 3: Effect of wrap wire shape........................................................................................................ 4 Figure 4: Uniform sand grains on wire-wrap (cross-section and plan view) .......................................... 5 Figure 5: Pre-packed screen cross-section............................................................................................ 5 Figure 6: Stratapac PMM screen............................................................................................................ 6 Figure 7: Internal gravel pack with CIV .................................................................................................. 7 Figure 8: CIV operation with IGP............................................................................................................ 8 Figure 9: EGP & ESS IPR comparison .................................................................................................. 9 Figure 10: Particle population, weight and volume ratios..................................................................... 12 Figure 11: Retention of uniform and non-uniform sands...................................................................... 13 Figure 12: Presentation of particle size data ........................................................................................ 13 Figure 13: Sand distributions illustrating different sorting .................................................................... 14 Figure 14: Sand plotted cumulatively to illustrate sorting..................................................................... 15 Figure 15: Gravel pore throats and sand particles ............................................................................... 16 Figure 16: Mesh pore throats and sand particles ................................................................................. 16 Figure 17: Field PSD data showing heterogeneous sands (plotted non-standard) ............................. 17 Figure 18: Field PSD data showing a very homogenous reservoir (plotted non-standard) ................. 17 Figure 19: Effective inflow areas of wire-wrap, pre-pack and multi-layer screens ............................... 20 Figure 20: Effects of fibre diameter on porosity (top). Effects of sand control media design on porosity (bottom) ......................................................................................................................................... 21 Figure 21: Unloading of non-fixed pore medium .................................................................................. 22 Figure 22: Media migration................................................................................................................... 22 Figure 23: Stress analysis plot ............................................................................................................. 24 Figure 24: Equipment set-up for laboratory mud qualification test....................................................... 33 Figure 25: EGP horizontal inflow.......................................................................................................... 35 Figure 26: ESS horizontal inflow .......................................................................................................... 36 Figure 27: Specific erosion for various types of screen including Stratapac screens. Data on competitors’ screens interpolated as required from SWRI data.................................................... 39 Figure 28: Effect of erosion on the size of the screen openings. A low open area medium is a lot more sensitive to slot erosion than a high open area medium...................................................... 40 Figure 29: Cross-sections of two outer protective cage designs.......................................................... 41 Figure 30: Gas erosion test .................................................................................................................. 41 Figure 31: Erosion resistance of Stratapac PMM screen as a function of gas velocity and particle size distribution. .................................................................................................................................... 42 Figure 32: Effect of cage design on erosion resistance ....................................................................... 43 Figure 33: Representation of the chisel effect showing the effect of impingement angle on the ease of penetration into the material. ......................................................................................................... 43 Figure 34: Effect of impingement angle on erosion rates of stainless steel......................................... 43 Figure 35: Schematic representation of the effect of a louvered cage on the impinging gas flow angle. ....................................................................................................................................................... 44 Figure 36: Screen Specification Schematic.......................................................................................... 46 Figure 37: Sand Control Decision Flow 1............................................................................................. 51 Figure 38: Sand Control Decision Flow 2............................................................................................. 52 Figure 39: Sand Control Decision Flow 3............................................................................................. 53 Figure 40: Sand Control Decision Flow 4............................................................................................. 54

Figure 41: Wire wrap jacket manufacturing process ............................................................................ 58 Figure 42: Shrink fit Dura-Grip screen.................................................................................................. 58 Figure 43: Wrap Wire Shapes .............................................................................................................. 58 Figure 44: Quality control of wire forming process ............................................................................... 59 Figure 45: Wire forming and inventory ................................................................................................. 59 Figure 46: 88 Spindle drilling machine (44ft jts) ................................................................................... 60 Figure 47: Wire-wrap screen types ...................................................................................................... 60 Figure 48: Wrap-wire profile ................................................................................................................. 60 Figure 49: Tensile testing of wire-wrap screens................................................................................... 63 Figure 50: Poisson effect of base pipe expansion................................................................................ 64 Figure 51: Free Flow Screen ................................................................................................................ 65 Figure 52: Free flow screen section ..................................................................................................... 65 Figure 53: Pre-pack configurations ...................................................................................................... 66 Figure 54: Resin coated gravel............................................................................................................. 67 Figure 55: Resin coated proppant (Carbolite) ...................................................................................... 67 Figure 56: Comparison between cured and uncured proppant permeability ....................................... 68 Figure 57: Pre-pack tower .................................................................................................................... 68 Figure 58: Steam curing process ......................................................................................................... 69 Figure 59: Isolation Sleeve .................................................................................................................. 71 Figure 60: Screened isolation sleeve ................................................................................................... 71 Figure 61: Stratapac screen (Range III) with solid rotating centralisers installed ................................ 74 Figure 62: SEM of Stratapac PMM medium......................................................................................... 74 Figure 63: SEM of Stratapac PMF-II media ......................................................................................... 75 Figure 64: Crush samples (left) and apparatus (right) ......................................................................... 76 Figure 65: Welded vs non-welded seals .............................................................................................. 78 Figure 66: Welded end-ring seal .......................................................................................................... 78 Figure 67: Longitudinal media welds.................................................................................................... 78 Figure 68: Construction and porosity of non-woven media.................................................................. 84 Figure 69: Comparison of PMF and pre-pack pore size distributions .................................................. 84 Figure 70: Stratapac media selection chart.......................................................................................... 86 Figure 71: Fine screens - plugging and retention................................................................................. 87 Figure 72: Plugging potential - 20/40 ................................................................................................... 88 Figure 73: Sand retention efficiencies .................................................................................................. 89 Figure 74: Challenge sand sieve analysis............................................................................................ 90 Figure 75: Media selection chart with challenge sand plotted.............................................................. 91 Figure 76: Coarse sand screen plugging resistance test ..................................................................... 92 Figure 77: Coarse sand - sand retention efficiency.............................................................................. 92 Figure 78: Coarse sand - effluent particle size distribution .................................................................. 93 Figure 79: PMF & DTW plugging resistance - normalised for porosity ................................................ 94 Figure 80: Openhole gravel pack ......................................................................................................... 95 Figure 81: Angle of repose (dry sand).................................................................................................. 95 Figure 82: Partial pack of long horizontal well...................................................................................... 96 Figure 83: IGP cross-section ............................................................................................................... 97 Figure 84: Typical perforation tunnel.................................................................................................... 98 Figure 85: Perforation packing ............................................................................................................. 98 Figure 86: Effective of formation damage ............................................................................................ 99 Figure 87: Example formation sieve data........................................................................................... 100 Figure 88: Limitations of Saucier's rule to gravel sizing ..................................................................... 101 Figure 89: 3D Gravel pack structure generated by 3D modelling ...................................................... 101 Figure 90: Gravel pack Pore Throat Distribution (PTD) ..................................................................... 102 Figure 91: Curve match of the gravel pack PTD with formation sand PSD ....................................... 102 Figure 92: Schematic of interfacing bridging ...................................................................................... 103 Figure 93: Bridging mechanism with example data............................................................................ 103 Figure 94: Productivity comparison for a various ESS & EGP completion options in a 6" heavy oil producer....................................................................................................................................... 105 Figure 95: Flow contribution along well bore of various ESS & EGP completions ............................ 106 Figure 96: ESS Construction .............................................................................................................. 107 Figure 97: ESS Assembly................................................................................................................... 108 Figure 98: Stabbing in ESS pin connection........................................................................................ 109

Figure 99: ESS Connections .............................................................................................................. 109 Figure 100: Expanded ESS ................................................................................................................ 110 Figure 101: Expansion Cone .............................................................................................................. 110 Figure 102: Expansion mandrel.......................................................................................................... 111 Figure 103: First 4” Compliant Rotary Expansion System (CRES) tool as used on Shell Brigantine 111 Figure 104: Non Compliant Rotary Expansion Subassembly ............................................................ 111 Figure 105: Compliant Rotary Expansion System ............................................................................. 112 Figure 106: Two trip installation: Trip 1 - Set Hanger......................................................................... 116 Figure 107: Two trip installation: Trip 1 - Expand screen................................................................... 117 Figure 108: Photographs following mud filter cake removal testing................................................... 120 Figure 109: Comparative screen plugging tests................................................................................. 121 Figure 110: Erosion testing................................................................................................................. 122 Figure 111: Sand exclusion testing .................................................................................................... 122 Figure 112: ESS connector strength testing....................................................................................... 122 Figure 113: ESS mechanical testing .................................................................................................. 123 Figure 114: Surplus expansion........................................................................................................... 124 Figure 115: Change of EST Radius with external pressure ............................................................... 125 Figure 116: Castlegate TWC testing with & without EST support...................................................... 127 Figure 117: Increase of Castlegate TWC strength with increasing internal pressure. ....................... 129 Figure 118: Effect of internal pressure on increase in TWC of loose sand and Castlegate sandstone ..................................................................................................................................................... 130 Figure 119: UBI log data illustrating borehole support ....................................................................... 132

LIST OF TABLES Table 1: Classification of sediments..................................................................................................... 10 Table 2: Gravel and slot size data........................................................................................................ 18 Table 3: Mesh size conversion table .................................................................................................... 26 Table 4: Wire-wrap metallurgy options................................................................................................. 45 Table 5: Stratapac metallurgy options.................................................................................................. 45 Table 6: ESS metallurgy options .......................................................................................................... 45 Table 7: Applications & risks for sand screen systems ........................................................................ 56 Table 8: Gravel pack risks .................................................................................................................... 56 Table 9: Weatherford screen features matrix ....................................................................................... 57 Table 10: Dura-Grip & Dura-Grip Plus standard dimensions ............................................................... 62 Table 11: WW Screen diameter change with temperature .................................................................. 63 Table 12: Micro-Pak standard dimensions ........................................................................................... 70 Table 13: Typical isolation sleeve dimensions ..................................................................................... 71 Table 14: Wire-wrap safe application limits.......................................................................................... 73 Table 15: Screen crush test - total suspended solids .......................................................................... 77 Table 16: Standard Stratapac screen dimensions ............................................................................... 79 Table 17: Standard Stratacoil screen dimensions................................................................................ 79 1 Table 18 : Standard Stratacoil screen safe application limits .............................................................. 80 1 Table 19 : Standard Stratapac screen safe application limits.............................................................. 80 1 Table 20 : Hi-Flow Stratapac screen safe application limits ................................................................. 81 Table 21: Recommended Stratapac base-pipe safe build angle application guidelines...................... 82 Table 22: Safe build angle application limits for Stratapac screen jackets .......................................... 83 Table 23: Standard Stratapac media ratings........................................................................................ 85 Table 24: Key to screen types .............................................................................................................. 90 Table 25: Media porosity comparison .................................................................................................. 93 Table 26: GP productivity comparisons................................................................................................ 99 Table 27: ESS application limits ......................................................................................................... 112 Table 28: ESS dimensional data (mm & inches)................................................................................ 113 Table 29: Operation time estimate ..................................................................................................... 115 Table 30: Surplus expansion (i).......................................................................................................... 123 Table 31: Surplus expansion (ii) ......................................................................................................... 123 Table 32: BHC testing ........................................................................................................................ 127

1. Introduction Scope The purpose of this document is to provide background technical information on Weatherford sand control systems for customers and application engineers, and to provide assistance in the selection of the most appropriate sand control system for any particular client application. The scope of this document is therefore limited to the areas of sand control were Weatherford equipment and services can make a positive difference to the client in terms of expenditure and well productivity. It will therefore not cover the history, geology, production and reservoir engineering aspects of sand control in detail except where Weatherford sand control systems have an impact.

Weatherford Completion Systems Capabilities & Contact Information A current overview of Weatherford is provided at the http://www.weatherford.com website. Weatherford consists of three major divisions: Drilling and Intervention Services (DIS), Completion Systems and Artificial Lift Systems (ALS). There is much interaction between divisions, especially during thru-tubing interventions with DIS and upper completions (eg gas lift) with ALS. WCS itself is sub-divided into distinct operating areas; North & South America, Far/Middle East and Europe/Africa/CIS. Local support is available through the nearest Weatherford location and strong centralised sand control support is therefore located in Houston, Aberdeen and Singapore/Kuala Lumpur. To contact the nearest Weatherford location, please visit the above website or contact the Weatherford offices listed on the cover.

Sand Control In the ideal world, sand control would be about preventing any solid particle from moving into the well stream and certainly from reaching the surface production facilities, while at the same time not introducing and additional skin or pressure drop to the completion. We attempt to do this generally by supporting the well-bore and filtering the sands downhole. However in the real world, every filter will plug in time. And so sand control involves getting the balance just right between producing small sand particles, which do not cause a problem at surface, and not plugging the filter system downhole. By directly supporting the sand face, we can reduce the number of large, load bearing sand grains from being produced. Therefore for effective sand control, we need to support, control and manage the sand face at the producing formations. This manual describes the technology currently available from Weatherford to perform this complex task.

Acknowledgements This manual was first developed to be used internally by Weatherford employees and is designed to be included in an intensive sand control training course. It has been subsequently adapted for use by external client and alliance personnel. Weatherford acknowledges the contribution in the form of much information from many sources including Shell International, BP, Chevron, Exxon/Mobil, Norsk Hydro, Statoil, Mobil, Pall Corporation, Schlumberger, Baker, Halliburton and USF Johnson. General Sand Control Information Manual External Revision 1.0 - 1

2. WCS Sand Control Systems Overview Background The causes of sand production and the reasons for sand control are covered in the general sand control course and other publications. An introduction to sand control can be found in an SPE series on special topics – “Sand Control” by W L Penberthy and C M Shaugnessy (ISBN 1-55563-041-3) which provides an excellent overview of conventional sand control technology prior to horizontal gravel packing, premium and expandable screens. Sand screens have been in use for over one hundred years in very many industrial applications, not limited to the oil industry. A wealth of information has been developed over this period and certain standard industry practices have emerged, especially with regard to gravel packing and wire-wrap type sand screens. When it comes to the newer metal mesh type and expandable screens, the old rules are called into question. Indeed, with the advent of horizontal wells, even the standard gravel packing and screen selection practices are receiving increased scrutiny. Conventional technology in difficult horizontal wells has a relatively poor record to date in terms of gravel pack placement and effectiveness. Weatherford Completion Systems with its unique sand control technology is forging a brand new path away from conventional capital intensive pumping technology and is focussed on providing customers with a safe and efficient means of achieving sand control while allowing maximum well & field productivity. It is however recognised that gravel packing (and especially fracture packing) still has an important place in the totality of sand control applications and these areas will be highlighted and addressed. Weatherford manufactures and supplies the sand control screens & equipment for standalone, gravel packing, fracture packing and expandable applications, and in conjunction with other service companies can also provide the full range of gravel and fracture packing technology. There are a number of companies involved in screen manufacture and the provision of sand control systems and services. The main competitors in terms of screen manufacture are: •

USF Johnson, a well established manufacturer of wire-wrap screens owned by Vivendi a French water and entertainment company. Johnson (not to be confused with Flopetrol Johnston, an old Schlumberger company) have acquired several smaller wire-wrapping companies including Effimax and Wesco. They have manufacturing locations in several locations round the world and are a big supplier to the water well industry. Johnson have recently introduced a premium screen.

•

Baker Oil Tools, a large oilfield service company provides several variants of slip-on wirewrap, pre-pack and premium screens, notably the Excluder, to complement its gravel packing services. BOT has a significant presence outside of the US.

•

Halliburton, through its Howard Smith acquisition and its Purolator (a US based filter company) alliance provides a similar product & service offering to Baker Oil Tools.

•

Other smaller manufacturers of screen only products (mostly wire-wrap) include Conslot, Nagoaka, Pippimas, Slotco/Citra, Tigaiken, Reslink and Cook. Secure Oil Tools manufacturing the Mesh-rite product have recently been acquired by Schlumberger. Many of these smaller companies are focussed primarily on the water industry (eg Cook) or are very regional in nature (eg Reslink).

General Sand Control Information Manual External Revision 1.0 - 2

Companies providing gravel packing and pumping capabilities to the oilfield are listed below: •

Baker Oil Tools, as mentioned above, have recently established a track record for the provision of horizontal gravel packs. The track record is worth examining in detail however. They promote their high-rate water pack technology as a viable method of gravel placement in long horizontal wells.

•

Schlumberger have adopted a similar approach and also promote their All-Pak shunttubes (licensed from Exxon-Mobil) as their way of getting a good gravel pack. Alternative Path Technology, All-Pak & All-Frac are registered trade marks of Schlumberger. Weatherford Stratapac screens have been supplied for All-Pak type applications.

•

Halliburton provide a similar package and are working on alternative systems to the Schlumberger All-Pak Screens.

•

BJ Services provide gravel packing services and systems, but do not manufacture screens.

•

OSCA provides also gravel packing services and promotes its Advance Pack system which packs the screens inside and outside with gravel downhole and hence by-passes any high leak-off zones and bridges in the annulus. Weatherford manufactures the system and screen for OSCA.

The sand control market is hence diverse and very competitive. The big service companies have much capital invested in pumping gravel packs and are therefore very aggressive in promoting this technology. Of the above companies, Weatherford supplies screens and mechanical accessories to Schlumberger, BJ and OSCA.

Slotted Liners The simplest form of sand control involves cutting slots in standard oilfield casing, tubing or liners. The slots are generally 1.5” to 2.5” long and their width typically varies from 0.012” to 0.250”. The smaller slot widths are cut with smaller circular saw blades and tend to be 1.5” long. Because the axle of the saw cannot pass below the tube surface, the end of the slots are under cut. Most typical slot patterns are staggered slots, but other variations are possible to shorten the manufacturing process. The open area of a slotted pipe ranges from 1.5% to 6% over the slotted length. Figure 1: Slotted liner

There are two types of slot available, keystone and straight (see Figure 1). The keystone slots are considered better than straight slots for their self flushing or cleaning ability. Keystone slots are generally twice as expensive as straight cuts. Slotted liners are only very slightly cheaper to manufacture than wire-wrap and are often more expensive. They are considered to be tougher but have much less open area. General Sand Control Information Manual External Revision 1.0 - 3

Wire-Wrapped Screens Weatherford manufactures wire-wrap screens in Houston, Singapore and Indonesia. There are three main types of wire-wrap screen; rod-based screens (Houston Free Flow™), pipebased slip-on (Houston Weld®) & pipe-based direct build (Dura-Grip®) screen. These screens are used in a variety of applications including the water well industry which is a very significant market on a global scale, disposal wells, environmental applications (eg land-fill sites) and of course the oil industry. Perforated API base-pipe Rib wires Wrap wire

End-ring or weld

Figure 2: Dura-Grip wire-wrap screen

Wire wrapped screens are normally made from triangular shaped wrap wire, see Figure 3. The gap between the edges of the wrap wire is sufficient to allow quite large sand grains to pass through. If rectangular wires were used, there is a possibility that odd shaped grains could be jammed or wedges into the groove and stopping other sand grains from passing. The triangular shape of the wrap wire reduces the chance of these large or odd shaped sand grains from getting trapped in the depth of the groove and hence plugging the screen.

Gap

Figure 3: Effect of wrap wire shape

These triangular wrap wires are also referred to as wedge or keystone shaped. In the water well industry, these screens are generally referred to as “wedge-wire” screens. Wire-wrap & pre-pack screens are discussed in detail in Section 5.


Figure 4 illustrates how wire-wrap screens control sand production by enabling the formation of sand arches or bridges. A sand arch is formed normally by two or three sand grains. Bridges formed with more sand grains are relatively unstable. As the sand bridges form, they restrict the passage of the other grains and these grains in turn bridge off over the initial arch forming a more stable structure. The formation of this stable structure or sand filter cake is key to controlling the passage of sand in through the screen and into the well stream. Cross-Section Generally, the fine and very small particles (fines) are able to pass through, whereas the large particles are stopped. The large particles cause the most damage in terms of erosion and clogging of the surface production facilities.

Plan View

The sand filter cake should be permeable. If the fines were stopped also, they would likely plug the smaller pores in the sand filter cake and hence reduce the overall permeability of the system. The open area under the sand filter cake adds significantly to the screen’s ability to allow fluid flow by eliminating dead space. If the size of the sand grains varies considerably, the filter cake formed would have a reduced permeability. Therefore, the ability of wire-wrap screens to control poorly sorted sand sands is limited. In general terms, wire-wrap screens are used behind gravel packs, which in effect have large, well sorted grains and can bridge off over the wire-wrap screen effectively.

Figure 4: Uniform sand grains on wire-wrap (cross-section and plan view)

Pre-Packed Screens Weatherford manufactures a variety of pre-packed screens including; Perma-Bond®, MicroPak® and Exact-Pak™ pipe-based screens and Muni-Pak™ rod based screen. Perma-Bond and Micro-Pak are generally used in oilfield applications and Muni-Pak and Exact-Pak are generally used in water well applications. Essentially the Exact-Pak and Perma-Bond screens are based on a Dura-Grip inner screen and a wire-wrap outer screen, with gravel or proppant sandwiched between. The pre-pack gravel (or ceramic proppant beads) is the main filtration medium and the wire-wrap jackets are designed to hold only the proppant in place. Perma-Bond screens are used in horizontal wells or marginal wells were the use of a gravel pack would be uneconomic. Micro-Pak screens are a slimmer design of the Perma-Bond screen and are primarily used behind fracture packs or high rate water packs in horizontal wells. The prepacked screens provide insurance against voids in the gravel pack. The rod based Muni-Pak screen has been very effective in municipal water well projects as an economic and effective sand control device in shallower water wells. Figure 5: Pre-packed screen cross-section General Sand Control Information Manual External Revision 1.0 - 5

Premium Screens Premium screens are typically an all-metal design, with a metal mesh filtration media and a protective outer metal shroud. The metal mesh can be either a metal weave, typically a dutch twill, or metal fibres or powder particles embedded within a square metal mesh. The apertures (called pore throats) generally very from 60 micron to 300 micron. The concept is for the mesh to prevent the larger sand particles from travelling through and allow the formation fines to pass. The larger particles form a permeable sand filter cake on the screen surface. Premium screens are typically run in long horizontals, often behind gravel packs and have similar sand control properties to pre-pack screens. The main improvements are the generally improved plugging resistance and, in most cases, the ability to flow back drilling muds through the screens. Weatherford Stratapac® PMM® 60micron screens were introduced in 1995 for high rate gas wells in the Gulf of Mexico. PMM is Porous Metal Media and is a sintered metal powder screen. Stratapac PMM screens generally are not used in drilling muds due to their small pore throat size. Stratapac PMF-II® (Porous Metal Fiber) screens can as they are rated at 120 microns or 200 microns, and hence allow the mud particulates to pass. Premium screens are discussed in more detail in Section 6. PMM and PMF-II meshes are trade marked by Pall Corporation and are manufactured for Weatherford. Figure 6: Stratapac PMM screen

Stratapac has the added benefit of being the most diameter efficient, non-expandable but highly porous premium screens on the market today.


Gravel & Fracture Packs Gravel packs (GP) and fracture packs are very useful techniques for completing sand prone reservoirs in a wide variety of sand types and completions. GP systems have been in common use for many years, and service companies and operators have built up a wealth of experience and knowledge. Gravel packing in open-hole (EGP – External Gravel Pack) is useful for preventing annular flow and controlling sand in heterogeneous formations. Gravel packing in cased-holes (IGP – Internal Gravel Pack) is useful for protecting the sand screens from erosional flow. After the liner is run and perforated, the sand face completion is run. The perforations may then be washed and the GP packer set. Figure 7 below illustrates the sequence of events involved. There are many tricks of the trade involved in getting a good pack and it is beyond the scope of this document to cover this in any great detail. Run sandface completion and set gravel pack packer. Squeeze gravel into perforations Flow is via open x-over tool Returns via open by pass area Circulate gravel pack, taking returns through shifting tool at bottom of inner string Ball lifted off seat Reverse circulate excess gravel from well X-over tool above packer

Figure 7: Internal gravel pack with CIV


When the GP operation is completed, it is necessary to remove the wash string and service tools prior to installing the upper completion. Often, some sort of loss control device is used in the sand face completion and the selection of such a device can greatly improve operation flexibility and efficiency. Figure 8 shows the use of a Weatherford Completion Isolation Valve (CIV) which can be opened and closed hydraulically. The other commonly used loss control devices are various types of flapper valves. The use of LCM pills in gravel packs and well screens is to be avoided and it is very difficult to return the pack and screen to full permeability along the entire well length. Pick up inner string and locate shifting tool in CIV. Pull ball closed. GP sliding sleeve open

Shear shifting tool and pull back. Close gravel pack sleeve. Pressure test and circulate to completion fluids GP sliding sleeve closed

Figure 8: CIV operation with IGP

Gravel packing becomes increasingly difficult and complex with hole angle and length. Also, in open hole situations, high permeability streaks (leak off zones) and washouts can interfere with the uniform gravel placement. Low net to gross pays with shales/clays can also intermix with the gravel during pumping and impair the gravel pack permeability and hence productivity. To counteract these problems, the industry has responded by developing specialised techniques and equipment, eg All-Pak® from Schlumberger (in co-operation with Johnson and Exxon-Mobil). This system uses shunt tubes on the exterior of the screens and allows the gravel to by-pass blockages in the well-bore annulus. Systems exist from other service companies, which aim to achieve the same result. For example, OSCA have developed an Advance-Pak® system (in co-operation with Weatherford), and Halliburton have their CAPS system. General Sand Control Information Manual External Revision 1.0 - 8

Expandable Systems The Weatherford ESS® system is currently revolutionising sand control operations. Developed in conjunction with Shell International, the system combines the ease of use and filtration capabilities of premium screens with the borehole support and flow conformance capabilities of gravel packs. The elimination of the annulus allows zonal isolation and remedial options as well as better production logging and reduces the risk of screen erosion. The large ID allows increased productivity and more uniform inflow over the length of the installed screen plus more flexibility in completion/remedial operations and ESP deployment. The mechanical deployment system eliminates most if not all of the fluid compatibility problems normally associated with gravel packing.

Well Slimming

IPR vs VLP 6" Horizontal 21 API Oil Producer 2,500 ft

3000

2500

2000

1500 VL ESS IPR (5.5" SHUNT GP IPR (2.44"

1000

Solution 6" ESS - 16,700

500

2.78" Shunt GP - 12,330

0 0

5000

10000

15000

20000

Flow Rate STB/D Figure 9: EGP & ESS IPR comparison

The benefit of increasing the screen ID is a marked improvement in well productivity as shown in Figure 9. This is a comparison for a 2500ft long 6” hole producing 21API oil between an ESS completion (5.5” ID) and a shunt-tube completion (2.44” ID). The solution points for the inflow performance and vertical lift performance curves indicate a significant 4000 stb/day difference in productivity. The increased productivity of an ESS installation in a 6” hole is comparable to that of a 6.5/8” standard screen in an 8.5” hole and so by using the ESS, a 6” hole is possible instead of an 8.5”. This will afford the operator tremendous savings in terms of casings and completion jewellery and also the possibility to use smaller and lighter drilling rigs. This concept is referred to as Well Slimming. The large bore of ESS allows more flexibility for ESP deployment. The use of ESS and other expandable technologies (liner hangers for example) should allow operators to realise significant cost savings and improve marginal project economics.


3. Sand Control Issues Operators generally have a number of concerns when it comes to selecting a sand face completion strategy. Primarily, revenue (expected production rates) and expenditure (both initial installation and also operational) considerations provide an envelope of possible solutions. Installation costs would include the totality of well costs as the type of sand face completion impacts on the hole size and drilling fluids used. Operating costs would include the cost of waste disposal and interventions required (eg ESP replacement or remedial sand control). To make decisions of the correct completion type to select it is important to be aware of the many sand control issues and the relative strengths and weaknesses of the products & systems available to the operator. A suggested method of narrowing down the choice of sand control system is presented in later in Section 4.

Sand Grains Clastic rocks, meaning rocks made up of grains, are classified according to the particle size of the grains. This is a fairly straightforward classification, for sedimentologists, the terms sand, silt and clay are defined in terms of the particle size. Sandstones are composed of sand-sized grains, usually quartz, and may be cemented together with another material. Clay minerals and other fine particles will be present in the pore spaces in varying amounts depending on the rock. Shales or mudrocks are made up of silt and clay sized grains. Table 1 gives a simplified classification. One micron (µm) = 0.001 millimeters (mm). SIZE (mm)

CLASSIFICATION Medium

8 Fine

Pebbles

GRAVEL

Sand

SAND

4 v. fine 2 v. coarse 1 coarse 0.500 medium 0.250 fine 0.125 v.fine 0.062 v. coarse 0.031 coarse 0.016 medium

Silt

0.008

MUD

fine 0.004 v. fine 0.002 Clay Table 1: Classification of sediments


The nature of a sedimentary rock depends on its depositional environment; sands may be deposited for example as beaches, river channels or wind-blown desert. The nature of the depositional environment will affect the size, shape and sorting of the grains. Later changes during burial will affect the sandstone’s cementation characteristics and strength. The later changes sometimes caused by volcanic activity, mountain building or tectonic movements can fault and change the direction of the beds. To decide on the most appropriate filtration or sand control system, it is very important to understand the size and types of sand grains that may impact the screen. Grain size definitions •

Sand - strictly particles between 62 µm and 2mm

•

Silt - strictly particles between 2 µm and 62 µm

•

Clay - strictly particles less than 2 µm

These strict definitions are not usually followed by engineers, you will find fine sands referred to as silts and fine silts as clays. Mudrocks and shales - engineers usually refer to all mudrocks as shales or shaly sandstones, mudrocks are composed of silt and clay. Fines can mean different sizes to different people and this should be clarified in any discussion. Silts and clays are understood to be ‘fines’, ie less than 62 µm. However, fines are sometimes defined as less than 44 µm.

Selecting Rock Samples for Particle Size Analysis This is not always easy! Often, core samples are available from exploration or appraisal wells. These samples when analysed cross many individual sand zones or beds (facies). The rock of most interest is the one most likely to produce hydrocarbons. If the reservoir is heavily faulted this might not be obvious. The zones most prone to failure (according to the rock mechanics data and models) need to be looked at closely. The core samples to be used for particle size analysis should be selected by visual examination and compressive strength measurements.

Particle Size Measurement Particle size can be measured a number of ways: •

Sieving (most common)

•

Laser diffraction using a Malvern or Coulter counter

•

Sedimentation – a gravity settling technique, really only used by sedimentologists and is not covered here.

For any particle size analysis the rock sample has to be disaggregated by hand into individual grains with a mortar and pestle. Mechanical methods such as milling are not suitable because the actual grains will be pulverised.

Sieving Sieving consists of assembling a stack of sieves so that the largest mesh opening is at the top with the mesh opening decreasing in successive sieves with the smallest at the bottom. At the very bottom is a solid container (called the pan) which collects the finest particles. The sand sample is put on the top sieve and the stack of sieves is shaken either by hand or mechanically, so that the sand particles fall down through the sieve stack until they are caught by a sieve whose opening is too small for the sand to fall through. At the end of the General Sand Control Information Manual External Revision 1.0 - 11

agitation period the sand fraction in each sieve is weighed. Around 10-20g sand is the minimum sample required for acceptable results

Laser Diffraction This method measures down to fractions of a micron and the amount of sand required is much less than is required for sieving (around 1g or less depending on the particle size, for these instruments the number of particles is important not mass). The sand sample is measured in water, and is agitated ultrasonically to aid dispersion. These systems are computer controlled, so that the machine indicates when the correct amount of sample has been added, etc. This method is quick and fully automated (apart from the adding of the samples!) and the data output can be varied, and plotted in terms of volume of fractions, or numbers of particles etc. The size ranges can also be varied. The drawback of this method is that it is limited in the maximum size of particle it can measure up to (usually around 1mm), also these instruments are extremely expensive.

Complications in Particle Size Measurement Measuring particle size is not as straightforward as it first appears, for the same sand sample different measurement methods can give different distributions. This is due to the shape of the grains. Dry sieving throws the sand grains around until they go through the sieve by the smallest axis, whereas, laser diffraction tends to take an average from randomly oriented grains. So if the sand grains are elongated or flat different distributions will result from the different methods of measurement. Another problem, which can happen with dry sieving, is that very fine particles can stick to the coarser grains. Sieving also generally only measures down to 45 microns, laser diffraction will measure down to fractions of a micron. Both sieving and laser diffraction give particle size as the equivalent spherical diameter, sieving gives the smallest equivalent spherical diameter and laser diffraction gives the average. Neither method gives any indication of grain shape and grain shape may be important in the sand filter cake permeability. Results from lab tests on screen plugging suggest that grain shape can affect the results. Sieve analyses report particle distribution in weight percent. A larger particle will make a larger contribution to the analysis than a smaller particle. This means that there are far more smaller particles in a given sand than the sieve analysis would indicate, and these particles may lead to screen plugging if the wrong pore size is chosen. Figure 10 illustrates the relative contributions to weight and volume a 1:1 distribution of particles make which differ by a factor of 2 in radius. Relative uniformity of the sample is an important parameter to consider in selecting a screen pore size. A screen may perform very differently with two sands with the same average size (D50) but very different uniformity coefficients. Figure 11 illustrates the results that may be obtained using a typical sizing rule (D10), where the screen ‘pore’ size is chosen at the 10th percentile of the sand particle size. Bridging efficiency (and permeability) is maximised by uniform sands, and minimised by non-uniform sands. The non-uniform sand is on the left.

Particle Ratio Radius Ratio Volume Ratio Weight Ratio

1:1 1:2 1:8 1:8

Figure 10: Particle population, weight and volume ratios General Sand Control Information Manual External Revision 1.0 - 12

Poor vs. Uniform Sand with Respect to Pore Size D10 =

D90 =

D50 =

Pore Size = D10 Figure 11: Retention of uniform and non-uniform sands

Particle Size Distributions The results of a sieve analysis or laser diffraction measurement of a sand sample are presented as a particle size distribution (PSD). Particle size data is generally plotted as cumulative weight–percent as a function of particle size on a log/linear scale. Conventionally, the data is plotted so that the accumulated weights start with the largest particle size (the conventional sizing rules are based on these plots) as in Figure 12. However, the data may also be plotted the other way around so that the cumulative weights start with the smallest size – this tends to happen with laser diffraction data. Cumulative ‘Weight’ Curve 100 90

% ‘weight’ curve

80

d90 = 145 microns

70 sand A sand A

60

d50 = 246 microns

50 40

d10 = 380 microns

30 20

Figure 12: Presentation of particle size data

10 0 10

100

1000

particle size (microns)


Another complication with these different ways of presenting particle size data is that particle size data is often referred to in terms of the diameter at certain percentiles. For example, the d10 is the particle diameter at the 10% point on the cumulative curve. The d50 is the particle diameter at the 50% point on the cumulative curve, this is also the median grain size. Where the data is plotted cumulatively from different start points (largest or smallest), this will obviously affect the size of these percentile points (apart from the d50). Common parameters are based on cumulative plots where the data is plotted cumulatively from largest to smallest. So that the d10 point refers to the largest 10%. It should also be noted that these particle size plots are based on mass (normally and incorrectly referred to as weight) which will emphasise the largest particles, because these will be more massive than the smaller grains. If size data is plotted in terms of numbers of particles in each size range, then the plot would look completely different with much higher values at the lower sizes. See Figure 10.

Interpretation The slope of the cumulative particle size curve expresses the sand’s uniformity or sorting. This is basically a measure of the spread in particle size of the grains making up the sand. The steeper the curve (the more vertical) the more uniform or better sorted the sand. Well sorted and uniform sands are composed of particles with a small spread in size. The flatter the curve the more non-uniform the sand, meaning that there is a large range in the particle size of the grains making up the sand. Examples of uniform and non-uniform sands are shown in Figure 13. The uniformity of the sand can be expressed as a ratio called the uniformity coefficient, this is also a measure of the sorting (though the actual sorting ratio used by sedimentologists is more complicated than this). The uniformity coefficient (Cu) is defined as the d40/d90. Sands with Cu below 3 are considered uniform, for values between 3-5, the sand is considered to be non-uniform, and sand with Cu’s >5 are highly non-uniform. This uniformity can give an indication of the sand’s propensity to plug a screen, the more non-uniform the more troublesome the sand. Note the Cu is always greater than 1.0. A well sorted (uniform) sand (B) and a more poorly sorted (nonuniform sand (C) as differential distributions

100 90 80 70 sand B

60

sand C

50 40 30 20 10 0 10

100 particle size (microns)

1000

Figure 13: Sand distributions illustrating different sorting


The same sands in now plotted cumulatively. Sorting coefficient Cu = ds40/ds90. 100 90 80

B Sand Cu = 1.6

70 60

(well sorted)

sand B sand C

50 40

C Sand Cu = 3.0

30

(non-uniform)

20 10 0 10

100 particle size ( i )

1000

Figure 14: Sand plotted cumulatively to illustrate sorting

The normal sand sieve analysis is plotted cumulatively with the particle size decreasing left to right and the weight sample increasing upwards. The typical curve is hence ‘S’-shaped. Figure 14 illustrates a curve plotted backwards from normal. A normal sand sieve analysis starts with the larger sieves and the grains fall through towards the smaller sieves, thus the weights are added from large to small. Thus, the d10 is always larger than the d90. Weatherford standard is hence to plot particle size on a logarithmic scale decreasing left to right and the weight increasing upwards, giving a ‘S’-shape. Caution is required when some companies or individuals plot the cumulative weight starting from the pan and adding from small to large sieves. They then plot the particle size increasing from left to right. This also gives an ‘S’-shape and can lead to confusion.

Media Sizing Rules This section briefly describes the existing work performed on screen sizing and is intended as background information. There are no definitive sizing rules on which to base screen slot or pore throat size selection. Work done in the past can give some guidance, but no exhaustive work has been performed on plugging and retention. Often, a size of gravel or slot has been developed for a particular field or area. Generally screen selection will be a trade off between retention efficiency and pressure drop, the better the retention the higher the pressure drop across the screen. This section will give a short summary of some of the main work and current thinking. Pioneering work on screen slot size selection was performed by Coberly in the ‘30’s. He concluded that spherical particles could generally be retained when the slot width was 2.5 times the particle diameter or less. Also with a mixture of sands of different sizes, the sand control properties of a screen mainly depends on the largest particles in the mixture. From this work he came up with his criteria of slot width being between 1 to 2 times the d10, here the d10 is the largest 10%. A criteria of 1 x d10 is commonly used in the Gulf of Mexico. For gravel packs, the previous criteria of 10 x d50 recommended by Coberly had led to failures in the Gulf of Mexico which led to a general reduction in the gravel sizing. Saucier did some tests with gravel packs in the ‘70’s. From this work, he came up with the 6 x d50 rule for gravel selection. This has formed the basis of much of the sizing of gravel packs since. General Sand Control Information Manual External Revision 1.0 - 15

More recently, work done by Amoco has tried to refine the Saucier criteria to concentrate the role of sub-44 micron particles in the plugging of gravel packs. In this work, sub-44 micron particles are referred to as fines and correspond to particles which can pass through a US 325 shaker mesh. Tests were performed on different sands with gravel sizes selected according to Saucier’s criteria. The sands used had high proportions of sub 44 micron particles (>10%). By using fuller descriptions of size distributions, ie the d10/d95, the d40/d90 ratios and the amount of sub-44 micron particles, guidelines were produced to assist in the application of sizing rules. These guidelines can be used to identify sand distributions where the application of the standard Saucier rule could lead to plugging. Per Markestad et al performed a series of tests on wire wrap screens and decided that a fuller description of the sand particle size distribution would give better indications as to the most appropriate slot width. In general, he found that larger slot widths than those predicted by Coberly gave the best results regarding plugging and retention. From this tests he produced a commercial computer programme ‘SANDS’, which gives recommendations on screen slot width. Most of this work has been centred around finding a suitable gravel size for gravel packing and then selecting a suitable mesh or slot size to retain the gravel. There is relatively little experimental evidence to support mesh sizing for stand-alone type applications. For this reason, it is currently recommended that screen sizing selection should be based on gravel sizing and confirmed by laboratory testing. However, most tests and theories indicate a stand-alone media pore throat to be within the d10 to d50 range depending on uniformity and fines content. warp wire weft wire

Sand screen mesh sizing protocol similar to gravel pack sand particle

aperture or pore throat

D = 630 microns D

d = 260 microns D = 2.4x d

D = 630 microns

d

d = 90 microns D = 6.5x d

Figure 15: Gravel pore throats and sand particles

Figure 16: Mesh pore throats and sand particles

Selection of Test Sands After having measured a range of samples from a reservoir, some sort of sand distribution has to be chosen on which to base either laboratory testing or the application of theoretical screen sizing rules. This can be a difficult decision if there is often a very wide variation in sand sizes and distributions. Although there is no laid down procedure to assist in this process, selection of a suitable sand is a matter of reviewing the available information and field experience. Figure 17 and Figure 18 show some typical particle size distributions which illustrate the difficulty in applying simple rules to mesh & media selection. General Sand Control Information Manual External Revision 1.0 - 16

1.00 0.90

cumulative weight (frac.)

0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 10

100

1000

10000

partilce size (microns)

Figure 17: Field PSD data showing heterogeneous sands (plotted non-standard)

Each line in the figure represents an individual sample sand taken at different point along a well or field or zone. Consideration would be given to the weakest sands, ie most prone to sanding and also to the sands exhibiting most permeability. If the data is from a vertical exploration/appraisal well, there may be sands included which would not be targeted in the development wells.

100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 10

100

1000

10000

particle size (microns)

Figure 18: Field PSD data showing a very homogenous reservoir (plotted non-standard)


Traditional Gravel Size Selection Gravels used in sand control are defined by their sieve sizes. For example, a 20/40 gravel is sieved between a 20 and a 40 US Mesh, ie particles range in size from 840 microns from 420 microns, with a median grain size of 584 microns. See Table 3: Mesh size conversion table. Saucier’s rule multiplies the formation df50 grain size by 6 to obtain the gravel grain size: dg50 = 6.df50 For example, if a formation sand has a median grain size of 100 microns, the median gravel sizing (according to Saucier) should be 600 microns, and a 20/40 gravel would be selected.

Gravel

Min Grain (µm)

Max Grain

Median Grain*

(µm)

(µm)

Gravel Pore Throat (µm)

Screen

Gravel Permeability*

Slot Size

(Darcy)

(inches)

12/20

840

1680

1260

200

450

20/40

420

840

630

75-90

121

40/60

250

420

335

45-50

45

.020 (500µm) .012 (300µm) .008 (200µm)

Table 2: Gravel and slot size data

* = approximate value A pore throat is the size of the smallest restrictions in a porous medium (rock or gravel pack) and so the pore throats associated with the gravel correlate with the median formation grain size when the Saucier criteria is used. Other rules or criteria include Schwartz, Stein and Hill but these are not commonly used. More details on gravel and slot sizing can be found in Section 7.

Wire-Wrap Slot & Mesh Sizing Wire wraps have been sized according to Coberly criteria, ie 1 to 2 times d10, and some companies base their slot sizing on d15. Meshes with their larger open area can be sized much smaller without plugging, somewhere equivalent to the d50 is often found to be the optimum size in tests. This means that much better sand retention is gained by the smaller aperture size, ie less small particles and ‘fines’ can pass through.

Sand Filter-cake Experimental evidence indicates that once a sand layer (filter-cake) has built up on the screen surface, no more sand is produced. This sand layer prevents fine particles from getting to and through the screen and protects the screen from further plugging. It is very difficult to provide an accurate estimate of the sand cake permeability. A rough estimate of unconfined natural sand ‘pack’ permeability is provided below: K = 760 . (df50/1000)2 . e(-2.8355 x LOG10(Cu)) where K is permeability in Darcies General Sand Control Information Manual External Revision 1.0 - 18

This value needs to be modified for packing, ie the pack structure, and for example requires to be reduced by about 30% for gravel packs. Other correlations exist to estimate the sand permeability, but more work is required to relate this to sand filter cake permeability. The overall filter cake/screen permeability will be improved by the gradual formation over the screen surface so that the filter cake is packed lightly and by increasing the porosity of the screen. For this reason, sand control completions should be brought onto full production gradually over as long a period as is practical (1 day to 6 months) and a bean-up procedure should be developed and discussed with operations/production.

Sand Samples To select the optimal screen and slot size, particle size analysis data (ideally from core material) from the relevant zones are required. Alternatively, actual sand samples would be satisfactory so that a measure the particle size distribution can be performed in-house. Listed below are the types of samples that might be available, in order of preference. Core Material (from full capture core barrels) The particle size analyses should have been performed on actual core material from the same formation that they intend to drill through. The distributions of most interest are those from the weak zones which are anticipated to fail during production. An indication of the spread in sand sizes that the screen will need to control is also necessary for correct slot size selection. Sidewall cores (from a wireline run core sample taker) These can be crushed and mud contamination can cause problems. Therefore distributions from these samples may not be representative, tending to be finer than the formation from which they were sampled. Rotary side-wall cores are an improvement over standard percussion types. Bailed samples (taken from the bottom of the well) These are not ideal and will only represent the coarse end of the produced sand, ie that which has not made it up the well-bore during production. These samples will be coarser than the parent sand and the distribution will give no indication of the sorting of the parent sand because the finer fraction will be missing, so both the size and amount of the finer material will not be known. Separator samples (taken from downstream surface separator As with bailed samples, these will not give a representative distribution of the parent sand. In this instance mostly the finer material will have made it into the separator, the coarse fraction will be missing. Additionally, the very fine particulates may have passed further down the process and so the remaining sample is in all probability not representative of the sand hitting the screen.

Open Area to Flow All filters will plug with time if they are doing their job. The bigger the open area/porosity, the more the resistance to plugging as there are more pore throats available and open to the flow path. Also the higher the open area/porosity, the lower the velocity of fluid flow through the media and the lower the pressure drop – less erosion and more production.


High Inflow Area A sand control screen needs to have highly porous media, but it is also important that the full surface of the media be exposed to the well flow. Figure 19 illustrates the typical open area associated with wire-wrap, pre-pack and mesh type screens. Wire Wrap Screens: Area

6-12% Open

Prepack Screens: 30% Open Area of Gravel under 6-12% Open Area of WWS or Perf. Shroud Multilayer Screens: 50-70% Open Area of Media Under Flow Distribution Layer

Figure 19: Effective inflow areas of wire-wrap, pre-pack and multi-layer screens

The flow of fluids through the screen (the screen face fluid velocity) is also important to consider. At low flow rates, this flow is likely to be laminar and at higher rates the flow becomes turbulent. The flow rate has an impact on which parts of the screen are exposed to flow and hence erosion. Generally, at high rates the flow does not change direction and finds the shortest path through the screen. Typical wire-wrap screens (WWS) have between 6-12% open area (with smaller wrap wires, this may be increased). The flow is straight through with a small diversion to the base-pipe perforation. The open area of wire-wrap screens can be improved by using very thin wrap wires, although this has the draw-back of making them more sensitive to damage and erosion. A pre-pack screen usually consists of either an outer wire wrap screen or a perforated outer shroud which has less than 20% open area. The pre-pack gravel (or proppant) has a porosity of 25-35%. At high rates, the flow is funnelled or concentrated over the base pipe perforations. Due to the random and three-dimensional nature of the pre-pack, it is no longer possible to measure the open area and hence porosity values are quoted. The porosity (and hence permeability) of the pre-pack can be improved by using very uniform and spherical grains or beads. Micro-Pak and Perma-Bond screens hence are typically made with a ceramic proppant which is more porous and permeable than the gravels commonly used by other manufacturers. Mesh screens have a higher media porosity behind a protective shroud. Some screens have drainage layers included to distribute the flow over the base-pipe perforations. Stratapac screens also have an outer drainage layer to distribute flow over the media. Most conventional screens have roughly similar outer diameters and screen lengths and so the screen surface area is similar. Certain screen types are slimmer than others and so a larger base pipe and hence outer diameter can be used. This is true of the Dura-Grip, MicroPak and Stratapac products. The area open to flow is hence this screen surface area times the open area % (or the porosity % assuming all the media is exposed to the flow).


A major advantage of the ESS product is the very large outer diameter, mesh media and no dead space at the couplings allowing it to provide the highest inflow area of all.

Maximising Media Porosity Another way of increasing the open area to flow is by increasing the media porosity in instances where increasing the diameter is a difficult option. Open area is key to minimising plugging, reducing local velocities, and providing low pressure drop across a screen. Figure 20 illustrates different types of media and how their construction relates to porosity.

Gravel

Woven Media

Non Woven Media

Porosity = 30%

Porosity = 45%

Porosity = 70%

Figure 20: Effects of fibre diameter on porosity (top). Effects of sand control media design on porosity (bottom)

The top illustration in Figure 20 shows how reducing fibre diameter increases the amount of open area in a given media. For well screen applications, mesh and pre-pack screens are often used in stand-alone situations or behind gravel packs as insurance. They are therefore exposed directly to the formation sands and so should be capable of controlling it. Typically three different types of media are employed; gravel (pre-pack screens), woven media (Dutch twill weave (DTW) and/or square weave mesh screens), and non-woven fibrous media. Gravel typically has a porosity of 25-35%, reflecting the large bulk of the gravel making up the matrix. Woven wire technology can increase the porosity to approximately 45-55%. Wire meshes can be made with larger open areas, but to do this would require either making a mesh with far too large a pore size for sand control or making a mesh with very thin wires which would have very little tensile strength. The design of weave has an impact on sand retention through the resulting aperture or “pore-throat” size, and also in fluid pressure drop. Weatherford uses woven wire technology in ESS and can also in Stratapac. Additionally in ESS, the weave has to be designed to be flexible to withstand the expansion process. The non-woven media used in Stratapac is made from a composite of powdered metal in a wire square mesh substrate (Porous Metal Membrane or PMM as shown in Figure 62) or sandwiching thin fibres in between square mesh substrates (Porous Metal Fibre or PMF-II (second generation) as shown in Figure 63). The woven mesh substrate has a large pore size, but high tensile strength. The non-woven fibres or powder have very high porosity and controlled, engineered pore sizes. This gives the PMF and PMM metal media the following important characteristics: General Sand Control Information Manual External Revision 1.0 - 21

•

High porosity range (50-70%)

•

Excellent sand control capabilities (β x filtration factor) for a wide variety of sand types and sizes. The PMF pore throat distribution closely matches that of gravel and generally correlates with the particle size distribution of the formation sands. This promotes interface bridging and the formation of permeable sand layers over the screen. See Section 7 on gravel pack sizing.

Fixed Media Construction For Stratapac screens, the filtration media is sintered to prevent ‘unloading’ and ‘media migration’. Sintering involves heating the woven and non-woven media to very high temperatures at which the individual fibres bond together and fuse to the restraining mesh. This means that the fibres are not free to move and hence the ‘pore-throats’ are fixed. Similarly for wire-wrap screens, the slot size is fixed. In pre-pack screens, the proppant is normally resin coated and cured at high temperatures to fix the proppant grains in place. ‘Unloading’ (see Figure 21) occurs when a particle is forced through a non-fixed pore medium under applied differential pressure. A fixed media will not give way to sand particles under normal applied differential pressures. Figure 21: Unloading of non-fixed pore medium

Media migration (Figure 22) occurs in non-fixed pore media when the media gives way under applied pressure or with high flow-rates and forms part of the flow stream. This occurs with some non-sintered fibre type (wire-wool) screens and leads eventually to premature screen failure. In ESS, the woven mesh is unsintered as some flexibility is required while the screen is expanded and the mesh needs to move over the basepipe. Note that the mesh itself is not expanded and retains its pore-throat sizing. The ESS has an extremely high open area to flow and so its performance should at least match and is expected to exceed that of unsintered premium screens.

Figure 22: Media migration

Draw-Down The pressure developed across a sand screen is often of concern to operators. In actual fact, a properly installed screen with good plugging resistance will develop very little pressure drop as the filtration media has a very high permeability and is relatively thin. The formation of a sand filter cake on the screen surface is much more significant and this is improved by a increasing the drainage area or pore throat density beneath the cake, ie increased media porosity and open area. Draw-down over the screen is mainly important in short length of screen with high production. High draw-down is also associated with erosional risks due the higher particle velocities expected. For horizontal completions, pressure drop associated with the screen is generally neglected. General Sand Control Information Manual External Revision 1.0 - 22

Borehole Support In gravel packs and ESS deployments, the well bore is supported to some extent. This means that flow in the well-bore and screen annulus is restricted or eliminated, and that the hole is prevented from collapsing. This has several advantages over stand-alone screen systems: •

Production is forced to flow directly into the screen allowing flow conformance

•

Flow conformance means that hot spot erosion channelling is unlikely (ie annular flow channelled into the screen at a point of well bore collapse).

•

Zonal isolation and treatment is possible

•

Load bearing sand grains are kept in place, reducing total sand production

•

Any collapsed well sections are prevented from producing increased sand quantities

•

Production logging and reservoir management is more effective

A certain amount of borehole support is provided by an ESS system, but there may also be a danger that the in-situ rock stress could cause collapse of the ESS. For horizontal and high angle open hole applications, an assessment of the rock stresses during depletion is recommended to ensure that these will not exceed the strength of the ESS. Weatherford has developed an analytical model for the generalised prediction of rock failure within a well-bore. The same model can be used to predict the point at which an Expandable Sand Screen will begin to elastically and plastically deform. Weatherford uses the model as a means of screening for ESS candidate well selection. Because of the spread of the analytical data points used to construct the model, caution should be used in interpreting the results to all rock types and potential stress regimes.

Basis of model design The rock mechanical input value used in this model is the Thick Walled Cylinder (TWC) test value of the rock. This is accepted as the best form of measurement of a particular rock’s reaction to the triaxial stresses imparted on it under relevant downhole conditions. This program corrects (reduces) the TWC value for hole size (TWC①) and corrects (increases) TWC① to compensate for the effect of borehole support, TWC②.

Borehole size correction - TWC① Larger well bores allow formation rocks to fail at lower applied stresses than those observed in the TWC test. TWC① is calculated from a linear regression plot of experiments carried out in 9mm, 115mm and 216mm holes using Castlegate sandstone with a typical TWC value of approximately 275 Bar. The correction has not been benchmarked for other sandstone types with different strengths. Work performed by van der Hoek of Shell International suggests the relationship between TWC and hole size remains approximately constant, irrespective of TWC.

Borehole support correction - TWC② TWC① is then corrected (increased) to reflect the support offered by the ESS. Under local failure conditions, failed particles of rock can be trapped in place by the ESS leading to a redistribution of stresses away from the ‘well-bore’. The ESS will not see load until this new ② steady state condition, TWC is again exceeded, at which point the ESS will start to see elastic deformation. General Sand Control Information Manual External Revision 1.0 - 23

Results of tests with ESS support in 4-1/2” hole have been used to determine the stresses required to initiate ESS deformation. In all tests, stresses much higher than the rock’s TWC① were required to elastically deform the ESS. These tests also showed that a stiffer ESS would increase TWC② failure point more than a weak ESS. Further, for a given ESS type, significantly higher TWC② values are obtained with increasing base TWC. This program has been calibrated on tests performed in loose sand and Castlegate sandstone. Again, a linear ② regression plot is used to infer TWC for rocks with strengths between the data points and beyond. The linear regression plot is considered conservative in its estimation of TWC② with ESS support.

Calculation of effective stresses The model assumes an isotropic, homogeneous reservoir. The applied vertical stress is calculated from the overburden gradient. The effective vertical stress is calculated from the applied stress and the prevailing reservoir pressure, modified by Biot’s constant (or poroelastic constant). Effective horizontal stresses are considered equal and derived from the vertical stress using the rock’s Poisson ratio. The maximum combined stress acting on a well-bore of a given angle is calculated from a force vector resolution of the effective vertical and horizontal stresses.

Results presentation The results of the modelling run are presented graphically as a plot of effective stress versus reservoir depletion. Once the resolved effective principle stress acting perpendicular to the borehole exceeds TWC② the ESS begins to elastically deform.

RESERVOIRSTRESS ANALYSIS PLOT 5000 4500

3500 3000 2500 2000 1500 1000 500 0 3100

2900

2700

2500

2300

2100

RESERVOIRPRESSURE(PSI) TWC

HOLE DIAMETERCORRECTEDTWC

ESS SUPPORT CORRECTEDTWC

ESS YIELDTHRESHOLD

Figure 23: Stress analysis plot


EFFECTIVE STRESSONHOLE (PSI)

STRESS / STRENGTH (PSI)

4000

Once this stress exceeds TWC② plus the ESS collapse pressure, permanent plastic failure of the ESS can occur. This line is represented as the “ESS yield Threshold”. This run predicts failure of the reservoir as soon as it is drilled since the effective stresses exceed the borehole support corrected TWC. Further, it predicts the ESS being loaded elastically throughout the reservoir depletion, but not plastically. The ESS could be used safely in this scenario with a 400 psi stress safety margin. The derivation of this model is discussed in more detail in Section 8.


Mud and Drill-in Fluid Conditioning Recommendations Drilling and Completion Fluids Weatherford Completion Systems does not supply drilling and completion fluids; however, it is recognised that the success of a sand control completion will be affected by the choice of these fluids. Communications between the fluids supplier and Weatherford Completion Systems is important to optimise the drilling mud and the well clean-up procedures to prevent formation damage and plugging of the screens. Normal sand control standard practice includes recommendations to minimise plugging of the screens at all the stages of the installation including handling of the screens on the pipe deck, making up the assemblies, usage of pipe dope, solids composition of drilling mud, removal of mud filter cake after screen installation. Mesh & Microns Conversion Table US Standard Mesh 6 8 12 14 16 18 20 25 30 35 40 45 50 60 70 80 100 120 140 170 200 230 270 325 400

Tyler Mesh

Microns

Mm

inches

4 6 8 10 12 14 16 20 24 28 32 35 42 48 60 65 80 100 115 150 170 200 250 270 325 400 477 565 673 800

4760 3360 2380 1680 1410 1190 1000 840 710 590 500 420 350 297 250 210 177 149 125 105 88 74 62 53 44 37 31 26 22 18.5

4.76 3.36 2.38 1.68 1.41 1.19 1.00 0.84 0.71 0.59 0.50 0.42 0.35 0.297 0.25 0.21 0.177 0.149 0.125 0.105 0.088 0.074 0.062 0.053 0.044 0.037 0.031 0.026 0.022 0.018

0.1875 0.1323 0.0937 0.0661 0.0555 0.0468 0.0333 0.0331 0.0279 0.0232 0.0197 0.0165 0.0137 0.0117 0.0098 0.0082 0.0069 0.0059 0.0049 0.0041 0.0035 0.0029 0.0025 0.0021 0.0017

Table 3: Mesh size conversion table


Open Hole Completions Overview The standard practice for open hole sand control completions is to drill the reservoir with a conditioned, screen compatible, non invasive, non damaging drill-in fluid. Screen compatible means that the solids composition is designed so that the majority of particles flow through the filter media. After the reservoir has been drilled, the mud is conditioned to maintain the particle size within the desired range. The open hole can then be displaced to a low solid content mud (base polymer in the case of water based mud) taking care not to disturb the mud filter cake. When the work-string is pulled out of the hole, the riser is then displaced to a filtered completion fluid. The screens are made-up at the rotary table and the filtered fluid displaces the air inside the screens without plugging the filter media. Having run in the hole with the screen assembly, it is a practice to displace the drilling mud to a clear fluid, often incorporating a breaker system, prior to bringing the well on production. However, this technique cannot always be practised for the following reasons: •

Displacement of long horizontal sections from synthetic mud to brine can be ineffective and result in damaging emulsions • Displacement of the open hole to clear fluids could result in large losses, with the potential for severe formation damage and a well control incident • For very heavy muds, the sand screen (eg pre-packs) cannot be selected to allow mud solids to pass through • The combination of formation and filter cake does not restrict hydrocarbon flow into the well-bore. An alternative clean-up strategy employed in some applications consists of conditioning the mud over fine shaker screens, running the sand control screens to bottom, and then back flowing mud through the screens without displacing to clear fluid or attempting to remove the mud filter cake. Nevertheless, experience using this technique highlights the following: • • • • • • • • •

The need to carry out formation damage testing on representative core samples prior to drilling the reservoir section Laboratory mud may give different results to field mud Careful control of excess emulsifier levels is required when the mud is run in the field Back production of mud through screens can be a viable technique, but carries an increased risk of screen damage and should be verified in the laboratory with field muds The key to implementing this strategy is very careful rig-site treatment of the mud to control the solids size distribution, including the use of screen plugging apparatus Pre-packed screen are more prone to plugging while single membrane screens allow drilling fluid solids to pass more easily Mechanical skins of around zero can be achieved with the right combination of filter media and optimised drilling fluid Good quality control is required in the mechanical integrity of the screens. Rotation of Pipe/Pump Rate - during pumping operations it is critical that the pipe is rotated as this will draw the clean-up chemicals into the low side of the hole. It is also important that any clean-up pills are pumped in turbulent flow to aid hole cleaning.

The final recommendations on well clean-up procedures should be the result of different tests taking into consideration the challenges and limitations of a particular development. It is recommended that laboratory (ie return permeability, mud cake clean up) and flow loop tests to evaluate screen plugging and formation damage potential are performed. Flowing General Sand Control Information Manual External Revision 1.0 - 27

mud once conditioned over fine mesh shaker screens, requires careful quality control of the mud properties on the rig site prior to running the screens to ensure the screens are not plugged either while running in or during initial hydrocarbon production. It is also recommended that steps be taken to ensure unconditioned mud cannot be introduced into the mud system for example through unconditioned mud lines or reserve pits.

Mud Cake Removal Open hole completion present a special challenge to screen because the mud filter cake must be removed or reduced after the screen is installed. The residual filter cake and insoluble drill solids collected in the cake can damage screens if not removed or treated properly. The best approach is to have as little insoluble solids in the fluid as possible and maintain a small particle size. This can be achieved by running the drill-in fluid through an efficient solids control system while drilling and monitoring the insoluble solids quantity and size. A suggested procedure to monitor mud quality is the mud plugging index test (MPI) described in the section on Lab & Well-Site Mud Conditioning Tests below. Each mud company will have recommendations regarding the pump rates required to achieve successful clean up of the mud filter cake. These are often hole deviation dependent, varying between 130 ft/min and 300 ft/min for horizontals. It is important to have as thin a cake as is safe and practical. The various muds have different mud cake properties. Oil base muds can have relatively thin cakes and some other mud types can have thicker or ‘fluffy’ cakes if not scoured properly. It is recommended to verify that such mud cakes can lift off and flow back through the screen without impairment. Removal of the filter cake can be achieved either by chemical dissolution or back flowing the cake through the screen. Successful back-flow of mud filter cake requires that the solids in the cake do not bridge or plug the media. For the mesh media this requires that the solids be typically less than 75 microns. Most drill-in fluids have particles well below this size. Larger particles, drilling debris and agglomerates can be minimised while drilling by conditioning the fluid system through shaker screens. To achieve efficient mud cake flow back, it is desirable to have a sufficient draw-down over the borehole wall along the length of the completion. For this reason, the cake lift-off draw-down pressure is very important. A low value is preferable to ensure the cake is back flushed entirely. For the Stratapac PMM and pre-pack type screens, back flowing the mud filter cake is not recommended unless a very fine (<30 micron) drill-in fluid can be used. All residual drill-in fluid in the hole must be displaced to a solids-free fluid before running the screens and the drill-in fluid must be conditioned while drilling through <53-micron (sub 270 mesh) shaker screens. The mud is sized to control losses into the formation and also to control the well. For heavy muds, the particle size may need to be quite large. Pore throat sizes of the formation can be estimated using the Kozeny correlation, r = ( 8 x ku / Ø )0.5 where r = pore throat size in µm ku = permeability in µm2 [to convert mD to µm2, multiply by 9.8717.10-4] Ø = porosity fraction For example, a uniform sandstone has a permeability of 480 mD and a porosity of 17%. The pore throat size can be estimated at ( 8 x 480 x 9.8717 x 10-4 ÷ 0.17 )0.5 = 4.72 µm


Another more common approximation is to use the square root of the permeability in millidarcies, ie r = (k)0.5 = ( 480 )0.5 = 21 µm From stable arch theory, it is assumed that particles down to 1/3rd of the pore throat size can be effective in bridging and plugging off the formation. Therefore the optimum particle size in the drill-in fluid would be between approximately 21 µm and 2 µm. These particles would easily pass through most mesh sand screens sized 100 µm and above. Mud particulates should be kept to at least less than a 1/3rd of the aperture size of the mesh. For example, an ESS 230 screen mesh should be used with a mud shaker mesh size of 77 microns or less. Referring to Table 3, the appropriate shaker screen would be a 200 US Mesh. For an ESS 150 screen, the particles should be less than 50 microns and hence a 270 or 325 US Mesh. Please note that in all cases, these are only guidelines and they should be confirmed by laboratory testing, field experience and in co-operation with the selected mud company. To summarise, the following procedures are recommended for optimum productivity of the mesh screens (Stratapac and ESS) in open-hole wells. Water Based Drill-in Fluids ESS & Stratapac PMF rd ! Shaker screens should be sized by the 1/3 rule. Condition drill-in fluid through mesh shale shakers while drilling to minimise size and amount of insoluble drill solids ! Monitor mud quality while drilling to maintain good flow through screens ! Displace residual drill-in fluid with “virgin” system containing only base brine, polymers and starches, leaving only a thin filter cake of drill-in fluid solids and insoluble drill solids ! Remove cake by back flowing through screen or dissolving in appropriate breaker systems. Stratapac PMM ! Condition drill-in fluid through 325 mesh shale shakers while drilling to minimise size and amount of insoluble drill solids. ! Monitor mud quality while drilling to maintain good flow through screens. ! Displace residual drill-in fluid with “virgin” system containing only base brine, polymers and starches, leaving only a thin filter cake of drill-in fluid solids and insoluble drill solids. ! Dissolve cake with appropriate breaker systems. Back flowing cake through PMM will not provide optimum productivity. Oil/Synthetic Based Drill-in Fluids ESS & Stratapac PMF rd ! Shaker screens should be sized by the 1/3 rule. Condition drill-in fluid through 200 mesh shale shakers while drilling to minimise size and amount of insoluble drill solids. ! Monitor mud quality while drilling using the MPI test to maintain good flow through screens. ! If possible, displace residual drill-in fluid with “virgin” system containing only base fluid with no bridging solids, leaving only a thin filter cake of drill-in fluid solids and insoluble drill solids. ! Remove cake by back flowing through screen ! An acid wash recipe can be formulated as a contingency wash procedure. General Sand Control Information Manual External Revision 1.0 - 29

Stratapac PMM PMM is best used in a sized salt system and is not recommended for oil-based or syntheticbased fluids. However, if necessary, the following procedures will minimise plugging. ! ! !

! !

Condition drill-in fluid through 325 mesh shale shakers while drilling to minimise size and amount of insoluble drill solids. Monitor mud quality while drilling with MPI test. Displace residual drill-in fluid with “virgin” system containing only base fluid with no bridging solids, leaving only a thin filter cake of drill-in fluid solids and insoluble drill solids. PMM cannot be run into solids-laden fluids. Back flowing cake through PMM An acid wash recipe can be formulated as a contingency wash procedure.

Cased Hole Completions Optimum performance of the screens can be obtained if all drilling debris and mud contaminants are removed from the well bore prior to running the screen. The procedures involved for preventing screen damage to fine pre-pack screens may involve running scrapers, viscosified pills, solvents, and circulating completion fluid filtered to 2 microns and preferably 0.5 microns (β>5000) until the NTU of the returns are below 25 – an onerous procedure and this may be relaxed with coarser mesh screens. Because of the variety of completions and fluids no single recommended clean out procedure can be provided, however some general guidelines are given below1. Fluid Cleanliness Criteria Before running the screen the return fluid cleanliness should be below 100 mg/L (100 ppm). Field experience has shown that the particle size distribution in filtered completion brine with 100 mg/L or less usually has 50 percent of particles smaller than 2 microns. However, clear fluid returns do not insure that the well has been displaced of all solids. For this reason displacement techniques should be incorporated which include mechanical and chemical clean up methods. A clean displacement fluid is required for the following reasons: • •

To prevent damage to the formation and screen from particulate matter To prevent solids interfering with the operation of down-hole equipment such as packers, hangers, etc. • To allow corrosion inhibitors to function by coating the screen, casing and downhole equipment. To effectively displace and clean-up the well it is very important that the following two criteria are met: Conditioning the mud A properly conditioned fluid will be least damaging to the screens, therefore it is very important to circulate and condition the mud in the pits as well as in the hole. Conditioning should heat the mud, reduce the viscosity and break down any progressive gel strengths, but not to a level where it loses its ability to suspend weight material.

1 Information provided by Well Flow Technologies, Inc.


Rotation of Pipe/Pump Rate During pumping operations it is critical that the pipe is rotated as this will draw the clean-up chemicals into the low side of the hole. It is also important that clean-up pills are pumped in turbulent flow to aid hole cleaning. The most effective displacements use a multiphase spacer system. comprised of the following:

The system is

Oil Based Mud • Base Oil • Weighted viscosified spacer • unweighted viscosified spacer • Solvent/surfactant wash • Unweighted viscosified spacer. The weighted and unweighted viscosified spacers should contain a water wetting surfactant with oil mud particle suspension action. The solvent/surfactant wash should include a blend of solvents and surfactants that will remove any remaining OBM residue including pipe dope, sand, barite and other solids on the metal surfaces. Synthetic Based Mud • Unweighted viscosified spacer • Sea water • Solvent wash • Solvent/surfactant wash • Unweighted viscosified spacer. The unweighted viscosified spacers should contain a water wetting surfactant with oil mud particle suspension action. The solvent wash should contain a blend of solvents specifically designed to remove pipe dope and oil based muds. The solvent/surfactant wash should include a blend of solvents and surfactants that will remove any remaining OBM residue including pipe dope, sand, barite and other solids on the metal surfaces Water Based Mud • Viscosified spacer • Sea water or brine • Solvent wash • Sea water or brine • Completion fluid. The viscosified spacers should contain a water wetting surfactant with oil mud particle suspension action. The solvent wash should contain a blend of solvents specifically designed to remove pipe dope and oil based muds.

Lab & Well-Site Mud Conditioning Tests Previous information highlighted the critical need to control mud quality to minimise screen impairment. Conditioning criteria must be determined by preliminary laboratory testing using the screen medium selected and the actual DIF to be used on the job (preferably a field sample). These tests will determine the shaker screen mesh size required to provide General Sand Control Information Manual External Revision 1.0 - 31

adequate protection against screen impairment and quantify the mud plugging index (MPI) to be used on the rig to control mud quality prior to running the screen in the hole. Example Mud Conditioning Qualification Test To select the shaker screen size that will remove mud solids to prevent screen plugging. The mud contained in the annulus between the screen and well-bore wall must be produced through the screen. Assuming a 1’’ annular space, this corresponds to a mud volume of 2.7L/ft² of screen (assuming a 5 ½ in screen inside an 8 in hole). Scaling it down to the screen sample size (2.5 in disk), this corresponds to 94 cc of mud. Using a safety factor of 10 (to account for possible damage during the running of the screen), the mud volume that must flow through the screen sample must be equal to 940 cc. A simple criterion to use is to pass 3 ‘lab barrel’, ie 1050 ml of mud through the screen2. The equipment required would consist of: • HPHT cell with 2.5’’ screen media disks and drainage meshes. • Sieves of various size (200, 230, 270 & 325 mesh). • Constant air pressure source (100 psi). • Graduated cylinder. See Figure 24 for set-up. Procedure 1. Install the screen samples at the bottom of the cell with the proper drainage mesh underneath and close the valve downstream of the cell. 2. Fill the container with unconditioned mud (approximately 500 ml) and pressurised the reservoir to 100 psi. 3. Flow 350 ml of fluid through the screen and relieve the pressure inside the cell. 4. Repeat step 2-3 a total of three times (to get a total mud throughput of 1050 ml) or record the total volume of mud throughput; 5. Change the screen sample. 6. Repeat step 1-5 with mud conditioned through 200 mesh sieve, mud conditioned through 230 mesh sieve, etc. down to 325 mesh sieve if necessary, until the required volume of mud (1050 ml) passes through the screen sample without plugging it.

2

This rule of thumb is used by BP in the North Sea (Clive Bennett, personal communication).


Pressure Source (Air or Nitrogen) 100 psi Pressure Relief Valve

HPHT Cell (500 mL)

Screen Sample (2 1/2" disks) and Drainage Mesh

Graduated Cylinder (500 mL)

Figure 24: Equipment set-up for laboratory mud qualification test

Example MPI Index for Use with Well-Site Mud Condition Testing To qualify a field test procedure that will be used to monitor mud quality and conditioning on the rig, prior to running the screen. This test is very similar to a Marsh funnel test but is designed to monitor plugging instead of fluid rheology. When plugging occurs, the leak off rate through the screen medium decreases. By comparing the leak off time, T1, of a first batch of mud (1 lab barrel), with that of a second time, T2, through the same screen sample, one can evaluate the plugging tendency of the screen and monitor mud quality. This test is designed to require very little equipment and expertise so that it can easily be run on the rig. The equipment required consists of: • • •

HPHT cell with 2.5’’ screen media disks and drainage meshes. Graduated cylinder. Stopwatch.

Procedure 1. Close the valve underneath the screen sample and fill the mud cell with 350 ml of unconditioned mud. 2. Open the valve and measure the time taken by the mud volume to flow through the medium, T1. 3. Close the valve again and fill the mud cell with another lab barrel. 4. Open the valve and measure the time taken by the second lab barrel to go through the same screen sample, T2. 5. Calculate the MPI: MPI = T2/T1. Note: When no plugging takes place, MPI = 1. As plugging increases, MPI increases. 6. Change the screen sample and repeat the test with mud conditioned through the sieve selected from the Mud Conditioning Qualification test. Note: in this test, no pressure is applied. The mud flows by gravity only. General Sand Control Information Manual External Revision 1.0 - 33

These two MPI indices obtained with the unconditioned and conditioned mud provides a range that can be used as baseline for the subsequent mud monitoring on the rig. Circulation through the shakers should be continued until the MPI is typically within 20% of the value obtained in the lab3. Note: the issue of using a new mud system versus the old one seems to be open to discussion amongst operators. Some prefer to use a new mud, free of drill solids; others prefer to continue using the old mud as it is better dispersed by the repeated circulation in the well.

Centralisers The centralisation of sand screens is highly recommended. This is thought to protect the screens during installation and to improve well bore clean out. For certain extended reach or unusual trajectory wells, some sort of centralisation is normally required to reduce friction and improve deployment. Weatherford has the most complete range of screen centralisation options available and has developed in-house software to aid in centraliser placement (Centro-Pro Plus) and also has Torque & Drag software for more detailed well planning requirements. For conventional type screens, Weatherford centralisers can be provided to customer specification at an additional cost. Typical centralisers are welded fins, spring bow, LoDRAG and LoTORQ roller systems and Spira-glider rotating centralisers. They can be placed: •

Top (Box) – if placed at the box, only one stop collar is required. Unless hinged, they must be installed prior to bucking-on the coupling. • Mid-span – two stop collars are required for centralisers placed between screen jackets. Unless hinged, they need to be installed during manufacture. • Bottom (Pin) – two stop collars are required for centralisers placed at the pin end. Can be installed at rig site. It is recommended for stop collars to be placed between the centraliser and the screen jacket end ring or weld. This is because the end ring or weld is tapered. If the centraliser hits an obstruction and is forced against the tapered weld, it can split and cause serious deployment problems. For this reason, it is recommended to install the centraliser at the box end so that it butts up against the coupling and not a screen jacket. It is recommended but not essential that Range 3 (40ft) pipe should be centralised in the middle of the joint (mid-span). Welded fin centralisers can be installed in various metallurgies and are normally used only in cased-hole applications. Special curved fins are available to prevent casing damage. Spring bow centralisers can be used in open-hole situations and are normally used in straight or partially deviated holes. Spira-glider centralisers offer certain advantages over normal zinc or cast solid rotating types, including the fact that they are crushable in the event of hole problems or irregularities, and they are lighter and malleable. Please refer to http://intranet.weatherford.com/EncycWeb/main.htm for details on the complete Weatherford centralisation systems available.

3 Other tests with mud samples conditioned with coarser meshes are also recommended to get a feeling of the sensitivity of the test with respect to particle size cut-off. Depending on the mud (mud type, solids loading, etc..), the MPI may vary and the recommended field MPI criteria may need to be modified.


Inflow Profile along Horizontal Wells Horizontal wells are increasingly popular especially in offshore areas where the number of wells to drain a reservoir is required to be limited. The trajectory of the wells and their intersections with the reservoir hydrocarbon accumulations is the subject of much study and computer modelling. To efficiently drain a reservoir with the minimum number of wells, it is advantageous to be able to produce along the entire length of the completion. It is often commented that horizontal wells only produce from the first 400ft (ie the heel). While this may an exaggeration, it is important to take steps to improve the productivity from the toe of the horizontal well. Apart from ensuring the formation damage is minimised and that the well is cleaned out properly to control completion skin, the most effective way to ensure uniform well inflow is to reduce the frictional pressure drop associated with horizontal completion. This can be performed in two ways, either reduce the number of perforations in the well screen or increase the screen internal diameter. In conventional screens, reducing the number of base-pipe perforations is feasible only with very low inflow rates associated with long production intervals. This approach has been adopted in the Norwegian sector. Even in this case, the inflow tends to be non-uniform and mainly from the heel. In such cases, inflow control devices have been employed to introduce choke at the heel to encourage production from the toe. Weatherford is developing a selfregulating device to perform this function, the Completion Inflow Regulator (CIR). The use of the CIR requires careful evaluation, because it in effect obtains production from the toe at the expense of restricting the maximum production rate of the well.

Gravel Pack

Figure 25: EGP horizontal inflow

Problems associated with the non-uniform draw-down along the screen length are illustrated in Figure 25. These include coning, inefficient reservoir sweep and drainage, poor mud clean-up at the toe, increased sand production and increased erosional risk at the heel. Another approach is the use of ESS; by increasing the screen ID, the frictional pressure drop associated with the base pipe perforations and inflow is greatly reduced. This has the effect of evening out the production inflow along the well, see Figure 26. Also illustrated is an expandable liner hanger greatly simplifying the well completion.


ESS Completion

Figure 26: ESS horizontal inflow

The use of ESS in horizontal wells has the following major benefits: •

Improved draw-down, clean-up and hence productivity at the toe

•

Overall increase in well productivity (less or smaller wells required)

•

Improved reservoir sweep efficiency (less wells required)

•

Possible well slimming cost savings (rig rates and completion equipment)

•

Less difference in draw-down along the well length (reduced coning tendency for water and gas)

•

Less fluid velocity in the reservoir (less erosional and sanding risk)


Erosion Resistance Sand screens may well be subject to various erosion mechanisms. Where erosion is expected to be a significant risk for the completion, the use of ESS, gravel packing and high flow screens should be considered. The high flow screens have increased base pipe perforation density. These applications should be discussed in detail with Weatherford. Erosion issues are always a consideration in every screen installation. In reservoirs prone to sand production, the sand grains are carried with the produced fluids and, if this rate is sufficient, can abrade and erode the metal structure of the sand control screen. The rate at which a screen is eroded is dependent on many factors: • screen design • screen metallurgy • particle velocity • angle of impingement • number of particles • particle hardness and shape. Erosion caused by actual gases or fluids is not normally a significant factor. From the above factors, the only effective ways in which an operator can mitigate against erosional risks is by controlling the particle velocity and screen design/metallurgy. Screen metallurgy is normally limited to stainless steel or an alloy material, such as Incoloy 825 or Carpenter 20Cb3, and this metallurgy is associated with the wire material used in wire-wrap based screens or the metallic mesh media used in the premium and the ESS® screens. In unusual circumstances, Weatherford does have alternative metallurgy and design options specifically for the premium and wire-wrap type screens. Please consult with Weatherford directly to discuss the applicability of these options.

Fluid & Particle Velocities Particle velocity is probably the most significant controllable factor and this can be reduced by either limiting production or by increasing the surface area of the screen exposed to fluid flow. Limiting production is not generally desirable and so increasing the surface area available to flow (open flow area) is the key area. There are several ways this can be achieved in open-hole situations: •

by using of deviated or horizontal wells can increase the overall screen length and area

•

by the use of a high porosity/open area mesh (Stratapac) or thin wrap wires

•

by selecting the optimum mesh/slot-size for mud compatibility and plugging resistance

•

by minimising dead space at connections on the screen (ESS)

•

by eliminating the annulus and ensuring flow directly into screen (EGP & ESS)

•

by increasing the OD of the screen (ESS).

Additionally, in cased hole (IGP) situations, the fluid velocity is determined by •

the shot density

•

the number (%) perforations open

•

perforation hole size.


In practice, although erosional issues should be considered in open-hole situations, the area of screen open to flow is normally sufficient to limit the downhole fluid velocities to within reasonable limits if the completion and deployment is performed correctly. The highest fluid velocities and hence greatest risk of screen erosion are normally associated with cased hole perforated liners.

Cased Hole Screen Completions Three main options are available: •

Stand-alone screen (insert & thru-tubing) – Stratapac, Micro-Pak & Perma-Bond

•

Some form of internal gravel pack

•

ESS.

There are often many factors which determine the optimum completion including zonal isolation considerations and, for the purposes of this report, the stand-alone screen and ESS options shall be considered here. This represents our current position and further work is underway to provide more definitive guidelines. The first step in evaluating the erosional risks associated with the screen completion is to calculate the downhole fluid volumetric flow rates. This is normally available from the operator or can be calculated from the surface production rates (gas, oil & water), fluid properties and reservoir conditions. Next, the velocity of the fluid exiting the perforations needs to be calculated. This will be the volumetric flowrate divided by the total area of open perforations. This area is determined by the perforation hole diameter multiplied by the number of perforations. This area should be discussed with the operator as the % of open perforations may be reduced with time and the possibility of re-perforating should be discussed. The use of high shot densities, double perforating and big-hole charges can be considered. Once the exit velocity has been calculated (with a 100% safety factor to allow for plugged perforations) this should be compared to the various screen designs. Typically, a limit of 0.1 ft/sec is applied to stand-alone screen completions. Above this limit, an internal gravel pack or ESS completion should be considered. For ESS, the limit is 0.27 ft/sec based on field experience.

ESS in Cased Hole Completions In unconsolidated formations, the perforation tunnel is likely to collapse and this can limit production. High shot densities and big-hole charges may not be sufficient. Oriented perforating should be considered to reduce sand production tendency. IGP in these situations can also be very problematical due to mixing the proppant with formation sands in the perforation tunnel. The collapse of the tunnel and its producibility would be related to the formation rock strength and sand characteristics, and it may be possible to predict tunnel collapse and well productivity from this information. In more competent formations, the tunnel may stay open and also in certain situations, the possibility of cavities behind the casing may exist. In such cases, the produced sand/fines will be largely retained at the ESS surface assuming the mesh is sized correctly. The formation of the filter cake of sand particles at the screen surface will protect the screen from erosion by the larger particles. It may be possible to pre-pack the perforation tunnels, prior to expansion of the ESS. Erosion from fines is a much slower process as the erosion rate is also dependent on particle mass. It is therefore advisable to bean the well up slowly to allow the cake to form prior to full production. The bean up period can be over several weeks and General Sand Control Information Manual External Revision 1.0 - 38

any prior sand production history would be useful information in deciding on the required bean up period. As the flowing perforations become filled with sand, the flow velocity in the remaining open ones increases. When calculating the erosion rate to decide on the bean up periods, a safety factor should be applied to the number of open perforations and account should be made of the typical field sand production rate in non-sand controlled wells.

Stratapac Liquid Erosion Tests Testing by Southwest Research Institute, conducted for the Erosion Joint Industry Project coordinated by major operators in the Gulf of Mexico, showed that under the extremely high flow-rate conditions (24kbpd/ft2) used for the testing, the erosion of the Stratapac screen medium (as measured by a parameter called Specific Erosion and defined as gram of metal removed per gram of sand ingressed) was relatively high compared to wire-wrap screens. It should be noted that in its standard configuration, the standard Stratapac screen is not designed for the extremely high and turbulent flow regimes experienced under the test conditions. The standard Stratapac outer and inner drainage layers are designed for normal laminar screen inflow conditions. The drainage area should be reconfigured to allow better drainage flow distribution if high turbulent flow rates are expected. This was achieved by using coarser meshes to slightly increase the space between the base-pipe and the filter medium while maintaining the screen structural integrity. The number of base-pipe perforations is also increased from 2” pitch to a 1.2” pitch.

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Specific Erosion (gm/gm)

An alternative method of improving drainage by creating a gap or a void underneath the filter medium (as in other ‘multi-layer’ screen designs) was not 1.50E-06 perceived as a viable option, as Volumetric Flux = 23,800 bpd/ft² this would have reduced the damage tolerance of the total 1.00E-06 assembly by allowing movement and flexing of the filter medium eventually leading 5.00E-07 to metal fatigue and/or puncturing. Erosion tests of the High Flow Stratapac screen 0.00E+00 design are shown below in Figure 27.

Figure 27: Specific erosion for various types of screen including Stratapac screens. Data on competitors’ screens interpolated as required from SWRI data.

Wire-Wrap Erosion Designs It is interesting to note that Figure 27 shows that wire wrap screen has the lowest specific erosion of all tested screens. Unfortunately, these results have not been correlated with variations in sand retention after erosion as this was deemed beyond the scope of the testing. A relatively simple model can be used to illustrate the importance of these variations in opening size as a function of weight loss for a standard wire wrap screen (90 gauge wire with 8 gauge slots (200 µm)) and a simple square weave mesh made of fine 200 µm round


Equivalent Slot Size (microns)

wire woven to make 200 µm square opening. Figure 28 shows the effect of erosion on the opening size, assuming certain erosion pattern for both wire shapes4. 400 Wire Wrap Screen (90 gage wire - 8 gage slot)

350

Square Weave Mesh (200 micron wire - 200 micron opening)

300 250 200 150

Erosion pattern

0

1

2

3

4

5

6

7

8

9

10

% Weight Loss Figure 28: Effect of erosion on the size of the screen openings. A low open area medium is a lot more sensitive to slot erosion than a high open area medium.

This simple model shows that despite its apparent high erosion resistance in terms of weight loss, weight loss erosion on wire wrap screen is much more significant than on multi-layer screens. In gravel and fracture packs, the erosional risks may be associated with the top most screens in only during the gravel pumping, ie for a short period of time. Weatherford has therefore developed special coatings and wire-shapes, which can mitigate against erosional problems in pre-pack and wire-wrap screens. Such design changes can only really delay erosional failures for a matter of hours or days, and as such they are expected to be used mainly on screens employed in gravel and fracture packs where the erosional risks are short lived.

Gas/Direct Impingement Erosion Gas erosion5 is different from liquid erosion in that the abrasive sand particles are generally more free to directly impact the metal surfaces of the screen as the gas can exert less effective contact pressure on the sand particle to counteract its inertia. Hence where the gas fluid path is tortuous, the sand particles impact the channel (screen) surfaces generally more so than in liquid flow streams. This gives prominence to the so-called ‘sand blasting’ or ‘scouring’ effect. This mechanism6 is dependent on the quantity, shape, relative hardness of the sand particles, their direction and speed and also on the metallurgy/geometry of the substrate. In comparing the abilities of different screens to resist gas particle erosion, the main parameters which can be controlled or otherwise affected by screen design is the particle mass, speed and direction and these would be primarily controlled by the outer protective cage design. 4 While the shape of the wire influences the erosion of the slots, the most important factor remains the open area of the medium, ie screens characterised by a low open area like a wire wrap screen are much more sensitive to slot changes than a high open area medium like the square weave mesh used in this example. 5 A more complete description of the testing performed by Scientific Laboratory Services is contained in Report SLS#6338 “Accelerated Erosion Tests on Stratapac and Baker Hughes Inteq Excluder Sand Control Screens” 6 The mechanism is more fully described in “Solid Particle Erosion and Erosion Corrosion of Materials”, Alan Levy 1995 (Library of Congress 94-73647).


Premium Screen Shroud Design There are currently two major types of effective screen cages available as shown in Figure 29. Outer Cage Media/Drainage Layers Base-Pipe

Louvered Cage Outer Cage Media/Drainage Layers Base-Pipe

Perforated Cage Figure 29: Cross-sections of two outer protective cage designs

Comparison Testing of Screen Designs in Gas Flow An in-house test apparatus was developed to test and evaluate the erosion resistance of sand screens under various gas flow conditions. Parameters such as gas velocity and sand particle size were optimised to provide sensitive detection of the erosion resistance of various screen designs. A comparison of the two cage designs using this test method demonstrated that the protection offered by baffles plates in a louvered cage design was not optimal and that erosion under the conditions tested was controlled by the removal of eroded material rather than by the sand kinetic energy. Also, a comparison between two Stratapac screens media (PMM and PMF2040 media) and Baker’s Excluder screen showed the superiority of the standard Stratapac screen design. Erosion Test Method An erosion tunnel was built to generate gas velocities (100-300 ft/sec) such as could be expected down-hole exiting from open perforations and to monitor screen erosion over a long time period. Screen samples were prepared by cutting flat 3.5" discs of screen material. Each screen sample was challenged with sand introduced into a high velocity air stream under various test conditions. Varying the line pressure controlled gas velocities, and a rotating disk assembly was used to determine the actual particle velocity at the point of impact. See Figure 30. screen composite erosion sensor to vacuum air supply blow er

sand inlet voltmeter

Figure 30: Gas erosion test


Effect of Gas Velocity and Sand Particle Size Distribution A series of tests were undertaken at two different gas velocities and using two different sands to determine the relative importance of these two parameters. Figure 31 below summarises the test results. It can be seen that the laws controlling material erosion are qualitatively respected; ie the heavier the particles and the higher the gas velocity, the faster the erosion. Not surprisingly, gas velocity seems to be the parameter affecting the most the screen erosion resistance. While sand particle size does not affect erosion as much, it is interesting to point out that even a relatively fine sand (d50 = 98 µm) is highly abrasive to the screen. 60

Time to Failure (hours)

50

40

46.3

35.3

30

20 13.1 8.5

10

0

Brazos Sand AFS60 Sand Brazos Sand AFS60 Sand 330 ft/sec 330 ft/sec 520 ft/sec 520 ft/sec

Figure 31: Erosion resistance of Stratapac PMM screen as a function of gas velocity and particle size distribution.

Erosion Resistance of Various Screen Designs In order to protect equipment against erosion, a known method is to force the abrasive particles to follow a tortuous path to reduce their kinetic energy and therefore decrease their abrasive power. This concept was tested using a louvered cage as a baffle to redirect the impinging gas flow. Figure 32 summarises the tests using the Stratapac PMM screen with its simple perforated cage as benchmark, and an alternate design in which the perforated cage is replaced by a louvered cage. It can be seen from the test results, that the louvered cage actually speeds up screen erosion instead of slowing it down as would be expected from the kinetic theory point of view.


Time to Failure (hours)

40

35.3

AFS60 Sand Gas Velocity = 330 ft/sec

30 20.7 20

15.1

10

0

Stratapac with Stratapac with Standard Cage Louvered Cage

Excluder 110 with Louvered Cage

Figure 32: Effect of cage design on erosion resistance

The difference in erosional rate is also affected by the particle impingement angle; ie the angle at which sand carried by the gas impacts the screen surface. The chisel effect of sand impinging a surface is illustrated in Figure 33, and the effects of angle of incidence on erosion rate is shown in Figure 34. 1 2 3

Figure 33: Representation of the chisel effect showing the effect of impingement angle on the ease of penetration into the material.

Erosive Wear (cm3/kg)

0.03

0.02

3

0.01

2 1 0 0

30

60

90

Incidence Angle (deg)

Figure 34: Effect of impingement angle on erosion rates of stainless steel.


At a normal or 90° angle of incidence to the surface, the erosion rate is at a low (Point 1 in Figure 34). At this high angle, the surface impacted by particles is compressed and workhardened, but there is no active mechanism to remove material from the surface. As the chisel or sand impingement angle decreases from 90 degrees, other effects begin to appear. For example, when the chisel is at a 40-degree angle to the surface, the erosion rate begins to increase (Point 2 in Figure 34). The erosion rate increases because material on the surface of the screen can be more easily removed or "kicked off". This is known as a chipping effect. This chipping or ‘chisel’ effect becomes worse at low angles of incidence. When the chisel or sand comes in at about 25 degrees, the erosion rate is at a maximum (Point 3 in Figure 34). Here the particles are gouging into the surface at angles which cause large amounts of material to be chipped away from the surface. At angles lower than 25°, the particles loose their energy by bouncing off the surface instead of chipping away at it, and the erosion rate goes back to a minimum value. Applying this theory to screen design appears to be correct under the conditions tested. These conditions were selected to be as realistic of direct down-hole gas impingement on sand screens as possible and suggest that the louvered cage might actually take particles that would otherwise hit the screen at 90 degrees, one of the least damaging angles, and redirect them into the screen at a more damaging low incidence angle, thus increasing the erosion rate (Figure 35).

Figure 35: Schematic representation of the effect of a louvered cage on the impinging gas flow angle.

Erosional Issues Summary •

Erosion of ESS and sand screens is the subject of further study during 2001.

•

Where high flow rates are expected and there is an erosional concern, the use of ESS, gravel packs and high low screens should be considered.

•

The fluid velocities through stand-alone screens (typically Perma-bond, Micro-Pak or Stratapac) should be limited to 0.1 ft/sec, above which gravel packs or ESS installations are required.

•

For short exposure periods (during gravel or fracture packing), pre-packed or Stratapac screens can be used at the top of the screens where the erosion risk is highest.

•

In cased hole situations, the state of the perforation tunnels and performance needs to be investigated.

•

Fluid velocities through ESS screens should be limited to 0.27 ft/sec.


Corrosion Resistance Weatherford provides screens in a range of metallurgies to survive the various downhole environments encountered down-hole. Dura-Grip, Houston Weld, Free-Flow, Micro-Pak and Perma-Bond screens can be provided in the following configurations: Base Pipe

Wire

Carbon Steels (N/L80, P110, etc) Chrome Steels (13Cr) Duplex & super- duplex Galvanised Steel 304 316L Incoloy 825

Table 4: Wire-wrap metallurgy options

Stratapac Screens are provided in the following configurations: Base Pipe

Carbon Steels (N/L80, etc) Chrome Steels (13Cr) Duplex & super- duplex

Mesh

316L Alloy 20 (Carpenter 20Cb3)

Shroud

316L (Alloy 20 if required)

Table 5: Stratapac metallurgy options

ESS screens are provided in the following configurations: Base Pipe Mesh Shroud Connectors

316L Super Duplex 25Cr 316L Incoloy 825 316L Super Duplex 25Cr Super Duplex 25Cr

Table 6: ESS metallurgy options

Most screens can therefore be provided in a configuration most well conditions and to combat weight loss and stress cracking corrosion. When concentrations and partial pressures of O2, CO2, H2S are present and especially in the presence of water and chlorides, it is advisable to consult a metallurgist to select the optimum metallurgy screen. In certain instances, it is also advisable to conduct corrosion tests. Screen construction and welding are qualified to the appropriate standards. Alloy 20 and Incoloy 825 are suitable by NACE standards and qualified for H2S environments.


Screen Specifications To obtain pricing & delivery information from the manufacturing locations, the customer services representatives would require detailed information on the equipment. An example customer specification schematic is included below in Figure 36. The intention would be to discuss the application in detail with the client and develop a screen specification which the client can sign off on. Customer services will provide a quotation based on this specification.

STRATAPAC CUSTOMER SPECIFICATION SCHEMATIC ABERDEEN MARKETING, VERSION 1.2, DATE 29 MAR 2000

OVERALL LENGTH TONG SPACING

JACKET 1 LENGTH

MID SPAN SPACING

JACKET 2 LENGTH

PIPE SPECIFICATION CUSTOMER SPECIFICATION APPROVAL NAME

THREAD TYPE

SLIPS SPACING

PIPE OD

CENTRALIZER TYPE AND LOCATION

MAXIMUM SCREEN OD

SIGNATURE DATE CUSTOMER NAME CUSTOMER LOCATION CUSTOMER REP WELL NAME FIELD NAME DRAW ING DATE SALES ENGINEER DW G REF # SUPERCEDES DW G REF #

P ARAM ETER MEDIA TYPE MESH/MEDIA METAL LURGY NUMBER O F MEDIA LAYERS DRAINAGE MESH OUTER CAGE CAGE METALLURGY NUMBER OF JACKET S JACKET 1 L ENG TH JACKET 2 L ENG TH T ONG SPACING SLIPS SPACING MID SPAN SPACING BURST TYPE FLOW TYPE

COMMENTS:

P ARAM ETER P IPE OVERALL LENG TH TOLERANCE ON LENG TH PIPE OD PIPE WT DRIFT ID PIPE GRADE THREAD TYPE MA XIMUM SCREEN OD NUMBER OF JOINTS REQ’D

VALUE FEET INCHES INCHES INCHES

DEFAULT OPTIONS R1, R2, R3 +/- 12 INCHES

API N80, 1 3CR-80 API, PREMIUM (SPECIFY)

VAL UE

FEET FEET INCHES INCHES INCHES

CENTRALIZER OD INCHES HOLE/CA SING ID INCHES MIN HO LE REST RICT ION INCHES PIN CENTRALIZER MID SPAN CENTRALIZER BOX CENTRALIZER ATT ACH CENT RALIZ ER SCHEMAT IC(S) A S REQ UIRED

DEF AULT O PT IONS PMF1220/PMF 2040/PMM 316L OR ALLOY20 PMF (2), PMM (4) INNER (1), OUTER (1) STD O R HI PERF 304L 2 13FT OR 15FT 13FT OR 15FT 18 INCHES (MIN R2) 14 INCHES (FIXED R2) 6 INCHE S (F IXED) STD, HIGH STD O R HI FLOW

SO LID, FIN OR BOW SO LID, FIN OR BOW SO LID, FIN OR BOW

INCHES

Figure 36: Screen Specification Schematic

For standard screens, the tong and slip spacings and the location of any centralisers is often omitted from any discussion or purchase order. These dimensions are crucial in ensuring a smooth and trouble free deployment. If the application requires more technical support, various dataforms are available to assist Weatherford and client personnel to acquire the relevant data and to aid in the selection of the most appropriate sand control technology. These would include special forms for torque & drag analysis and in-situ stress calculations, as well as metallurgical recommendations. See Section 4 below for more details on the required information.


4. Sand Control System Selection To make the best decision on what type of sand control system should be employed, an operator needs to consider a large range of options. The decision processes involved change around the world. In the Gulf of Mexico, service companies and rigs are geared up to react quickly and the techniques employed are generally well tested and proven in that area. In offshore West Africa for example, where the supply chain is longer and communications a bit more difficult, projects require more long term planning. New fields, especially North Sea or deepwater, generally take months or even years in the planning phase and each option is considered in detail. Weatherford therefore has to cater for the market demands and make its proposals and recommendations in a timely manner. These proposals are normally made in response to a specific customer request, but some times the enquiry is more general. It is in Weatherford’s best long term interest to ensure its equipment is used and applied correctly. In each case, Weatherford should make its best effort to examine and discuss each request in order to ensure the equipment supplied and installed best meets the expectations of the end user. To make a recommendation to the client, Weatherford would require to gather some background information on the proposed application. Using this information, a number of possible screen and deployment options are likely to be identified. This information is fed back to the end user and an assessment of each option would be made. This assessment may take the form of a detailed net benefit analysis involving production modelling and rig design, or it could be a straight forward comparison of price quotes as the completion type has already been decided upon. It should be pointed out that the advent of expandable screen solutions require that even previously straightforward client sand control decisions be re-evaluated.

Background Information Required When preparing to select a suitable sand control system for a field of well, there is a number of important questions to be addressed and an amount of back-ground information is required. To assist in the gathering of the required information, a Sand Control Dataform is available from Weatherford. This is provided as an attachment. If this is not available, below is a summary of the information requested.

Company & Contact Information •

Details on the operator and its partners is often useful to improve the sharing of information.

•

Contact information is also mandatory.

•

A delivery date required (if applicable) for any equipment together with the expected installation date or well programme.

Well Profile Information •

Field name

•

Well name

•

Location (onshore/offshore/swamp)

•

Rig type (jack-up / semi / platform, etc)

•

Well type (Production/Injection/Gas Storage) General Sand Control Information Manual External Revision 1.0 - 47

•

Completion - (cased/open/thru-tubing)

•

ESS expansion diameter required

•

Minimum hole restriction

•

Expected setting depth (measured & vertical: top and bottom)

•

Well inclination at setting depth

•

Casing (previous casing if open-hole) - size, weight, grade

•

Shoe depth (measured/vertical)

Please state the units used.

Equipment Requirements •

Metallurgy requirements

•

ESS expansion diameter required

•

Filtration requirements (nominally 60 – 300µ) (supply sieve data if available)

•

Is borehole support or conformance required?


Formation Data at Setting Depth •

Formation type (ie sandstone, sst/shale)

•

Rock strength - TWC, UCS (specify)

•

In-situ stresses - minimum & maximum

•

Rock properties (if known - Poisson’s ratio, Young’s modulus)

•

Overburden gradient

•

Formation characteristics (permeability, porosity, shale content)

•

Requirement for or possibility of zone isolation

•

Pore pressure gradient

•

Break down gradient

•

Formation fluid type (Oil, Gas, Water)

•

Fluid used to drill reservoir (type of fluid & weight)

•

Reservoir completion fluid

•

Expected downhole flowrate(s)

•

Expected reservoir pressures/temperatures (Initial, Depleted)


Additional Comments & Information •

Please add or attach any other information / drawings that may assist in the preparation of your technical proposal.

•

Well plan or final directional survey including: Measured depth, TVD, Deviation, Azimuth, dog leg severity General Sand Control Information Manual External Revision 1.0 - 48

•

Additional information required to correct depth measured from drilling rig with depth measured from work-over rig

•

Perforation details if any

•

Production history if any

•

Provide produced/injected fluid properties (eg Heavy oil, wax, asphaltenes, H2S, CO2, Cl-)

•

Well schematic (including completion) with dimensions, depths, casing specifications, cement top

•

Sieve analysis

•

Mud/well logs

•

Summary of any problems experienced (and their reasons) when drilling and completing the well, ie well control problems, fluid losses, differentially sticking, well-bore instability, cavings, bad cement job, fishing, side-track(s).

•

If there were problems with fluid losses, specify the type of LCM used and its efficiency

Previous Experience To determine the correct system and media sizing, it is extremely useful to know if the operator has used other methods of sand control, eg what type and what happened. Sand Production Any information on the amount of sand production that can be tolerated, for instance the use of ESP’s etc will restrict the amount of sand that can be produced Injection/Production Rates Again, this is important when considering erosional and screen system sizing. Fluid Properties (Produced and Injected) The presence corrosive chemicals will affect the screen metallurgy. asphaltenes may also affect media and screen type.

Heavy oils and

Selection Process A method of selecting the most appropriate open-hole sand control system is depicted in the flow charts overleaf. These charts are for guidance only and are designed around a new hole well. The selection process would also be broadly applicable to cased hole and workover wells.

Chart 1 – New Well Decision Tree This covers gathering the background information available in order to make an initial assessment as to the requirement for sand control. Obviously in some cases the requirement is well established, but for new fields this may not be so obvious. Especially at the end of the field life when the reservoir is at depleted pressure and beginning to produce higher water cuts. In some cases, installing sand control systems later in the field life is practical, but for deepwater or subsea wells this is unlikely. Legal options for the disposal of produced sand, sand monitoring and sand traps together with sacrificial erosional sections in the production process equipment need to be evaluated.


If a screen based sand control is not installed initially and other steps are taken to reduce or control sand production, for example sand consolidation (SCON), oriented perforation or production rate restriction, it is well worth considering what remedial actions are possible as a result of the decision. Even when sand screens have been selected, the remedial and work-over options need to be considered. Once, a mechanical form of downhole sand control has been decided upon, the next big question needs to be examined – whether borehole stability and well flow conformance control is required. If it is thought that a collapsed well on a stand-alone screen may damage productivity or that annular flow needs to be eliminated. If zonal isolation and control is required, then an ESS completion would be optimal.

Chart 2 – Remedial Options Decision Tree Once the sand control method has been selected and implemented, the well production is monitored for sand. If this is excessive, the well is choked back until and acceptable sand rate is achieved. If production is now too low, a number of remedial options need to be evaluated. These include •

Clean-up & ESS Screen installation. This will probably involve pulling the upper completion and installing the ESS. The advantage to this procedure is that a relatively large ID is left for production and for further remedial and zonal isolation options.

•

Clean-up and install a thru-tubing screen (eg Stratacoil). This is quick and inexpensive but results in a smaller ID and hence a reduced production rate. For smaller and older wells, these has proven to be very effective. In the future, new deployment methods will allow installation of ESS in many thru-tubing applications. Certain ‘monobore’ applications are possible with ESS now.

•

Clean up and install an insert screen (eg Micro-Pak or Stratapac). Again, this will involve the removal of the upper completion and the installation of an insert screen. The screen should be as slim as possible to provide maximum inflow area with maximum internal diameter for production.

•

Side-track the well and install sand control. Possibly an economic option when the well expense is compared to increased production.

•

Drill and complete a new well. The last resort, but again may be economical in certain situations.


Figure 37: Sand Control Decision Flow 1




Figure 39: Sand Control Decision Flow 3 General Sand Control Information Manual External Revision 1.0 - 53


Chart 3 – Well Flow Conformance Decision Tree Often the option to gravel or fracture pack or even run ESS is forced upon the operator by erosional and flowrate concerns. In some instances, the rates are so high that even ESS and gravel packs are risky. In these cases, there is no option but to reduce the rates or redesign the well trajectory or completion. General Sand Control Information Manual External Revision 1.0 - 54

ESS screens offer many and considerable advantages over gravel packs. However in deviated or horizontal wells, there is a possibility that the in-situ rock stresses may overcome the support provided by ESS and fail the completion. In these instances, a gravel pack would be required. For this reason, a good knowledge of the rock strengths in the open hole sections are required. Generally speaking, the overburden pressure is normally the largest stress and so other in-situ stresses are less important in horizontal and highly deviated wells. If the other advantages offered by ESS are also important, it may be worthwhile re-planning the well trajectory or changing the hole size to accommodate the ESS. If an ESS cannot be run due to rock strength limitations, note that this will also affect the complexity and success rate of the gravel pack. If the well has a low net to gross ratio (ie shales, mudrocks and silts/clays are evident) or if the well has some high permeability streaks or if the well is highly deviated (>62 degrees and certainly greater than 80 degrees), then the resulting gravel pack operation is likely to be very complex. Specialised techniques and experienced personnel would be required to achieve an adequate gravel pack. The use of shunt tubes should be considered. In reality, even companies with experience in pumping long horizontals would not guarantee achieving a perfect pack and so would use premium screens behind the pack. Depending on the circumstances, it may be possible to use a Micro-Pak screen also. With gravel packs, the screens should be as slim as possible and hence Stratapac and Micro-Pak screens are candidates in this instance. If a normal gravel or fracture pack is possible, then Dura-Grip, Houston-Weld, Micro-Pak or Stratapac screens can be used. If a fracture pack is expected or there is a risk of erosion during the pumping operations, the top screens should be more erosion resistant and so a pre-pack or premium screen can be used. In extreme cases, specialised erosion resistant screens are available. If ESS screens are suitable then the completion options are simpler. If either increased productivity, reservoir sweep efficiency, well slimming, or OBM DIF are needed then ESS would be the preferred option. Also, if the well has any propensity to coning (either gas or water) then again ESS is preferred.

Chart 4 – Stand Alone Screens Decision Tree Often an operator will install a stand-alone screen if the well is extremely long or if the onset of sand production is not expected to occur until much later in the life of the well. If a standalone screen is suitable option, the first step is to select the most appropriate media to control the expected sands. This will often narrow down the choice of screen to a very limited number of possibilities. Coarser well sorted sands can be controlled perfectly well by wire-wrap screens. If an operator is concerned about deployment damage or quality, a double wire-wrap or pre-pack can be considered. For poorer, less well sorted sands and longer completion lengths, premium and pre-pack screens are the main options. If high erosional flowrates are expected, alternative screen designs can considered before utilising a gravel pack or ESS option. And finally, the mud system should be selected to be compatible with the screen and media. For example, OBM systems which give improved hole stability and shape can be used with ESS, PMF Stratapac and Dura-Grip, whereas completion brines can be used with all screen types. Generally, unless in very heavy muds, it is possible to modify the drill-in fluid properties to pass through the screen.


Risk Management The above process should have allowed the operator to decide upon a short list of technically suitable candidate systems. The next step is to examine these in more detail and quantify the risks associated with each system and their overall costs. Most clients will of course introduce their own priorities, contracting arrangements, experience and subjectivity into this process. Table 7 below illustrates the applications and the relative risks involved with each stand-alone screen type from the Weatherford perspective. The risks would need to be evaluated for each application against the required production, projected life of the well and the cost of any remedial operation. Note that some risks can be designed out or mitigated by changing the completion procedure, auxiliary equipment or by modifying the standard screen design. For example, it is possible to include a protective shroud on the Dura-Grip which would mitigate against deployment risks.

Table 7: Applications & risks for sand screen systems

Table 8: Gravel pack risks General Sand Control Information Manual External Revision 1.0 - 56

Table 7 shows that each screen system has its own risks, which need to be considered. Installing the screens behind a gravel pack will mitigate against some risks (namely erosion and sand plugging), but will introduce other risks associated with the gravel pack itself. Table 8 compares the screen risks associated with gravel and fracture packs. Note this table does not include the risks of the actual pumping operations themselves, eg high permeability streaks, bridges, etc.

Weatherford System Advantages Table 9 compares Weatherford screen systems with their equivalent competitor screens and lists their positive advantages. Although, in Table 9 the actual productivity differences between the various sand screen products (like-for-like) is relatively little, the productivity differences between various completion types (eg IGP, EGP, stand-alone and ESS) can be considerable. Feature

Effect

Advantage

Dura-Grip compared to Standard Oilfield Wire-Wrap No rib stand-off

Uniform rotational wrap deformation, returns when base-pipe untorqued

Rotational limit increased

No rib stand-off

Jacket 'push off' strength increased

Local tension/compression limit increased and more damage tolerant during deployment

No rib stand-off

Wrap tensioned with base pipe expansion (Poisson effect) counters Sand control maintained at high temperatures metal expansion with temperature

Wire-shape

Promotes stable filter cake formation

Improved filter cake permeability*

Micro-Pac compared to Standard Oilfield Slim Style Pre-Pack Superior sphericity on grains gives less friction during pre-packing

Elimination of pre-pack voids

Mitigation of erosional hot-spots from screen pre-packing

Steam resin curing

More even and controlled curing process

Mitigation of erosional hot-spots from screen deployment

Superior sphericity on grains gives improved pore volume

Improved permeability and plugging resistance

Longer screen life and higher productivity

Stratapac compared to other Premium Screen Types Highest media pore volume

Improved plugging resistance and dirt holding capacity

Longer screen life and higher productivity

Highest media pore volume

PMF can be used in a wide variety of sand types

Suitable for long heterogenous intervals

PMM 60 micron filtration

PMM provides finest filtration capability

Suitable for very fine sands (gas wells)

Multi-layer construction

Multiple barriers to sand

Longer screen life

All-welded and offset construction

No elastomers, folds or crimps

No direct flow through paths in the event of failure

ESS compared to Gravel Packs Borehole conformance

Highest completion ID High(est) Inflow Area Lowest frictional pressure losses Borehole support

No fluid compatablity problems, no specialized pressure pumping units and personnel, less rig time, simple completion, simple logistics and less safety hazards => improved well economics. Zonal isolation and remedial treatments are effective. Less frictional pressure drop along well length, can drill a slimmer Higher well production capacity & improved well well for the same production ID, can run larger remedial equipment economics => well slimming More mesh apertures open to flow, longer to plug. Low fluid velocity Longer completion life leading to improved well through screen and therefore less erosion. economics Reduced gas & water coning tendency, improved More uniform drawdown along drain length, better filter cake removal reservoir sweep efficiency* => improved field economics Formation remains intact as load bearing sand grains are supported, Any fines that flow are produced, improving completion less fines plugging skin with time* => longer completion life Gravel and specialised fluid programmes are not required. Fluid communication up screen/wellbore annulus curtailed.

Table 9: Weatherford screen features matrix


5. Wire-Wrap Screen Solutions The manufacturing process involves forming the steel wires themselves and then wrapping the formed triangular wires over the straight rib wires in a lathe like machine. As the machine rotates, it electric welds each rib to the wrap wire. The wire dimensions, gauge, number of ribs, metallurgy, jacket OD, jacket length and weld strength determines the time taken to manufacture one jacket. Figure 41: Wire wrap jacket manufacturing process

For pipe-based screens, the base-pipe is perforated by a drilling machine and deburred ready for installation of the screen jacket assembly. The base-pipe is normally threaded and coupled and can be carbon steel (typically J55 to P110) up to super-duplex. The customer would normally specify the type and threading depending on his application. Once the jacket has been made, it is cut to length and “slipped on” to the perforated base-pipe. In the case of Dura-Grip, the screen jacket is wrapped SLIP-ON directly on to the perforated DURAbase-pipe in effect ‘shrinkSCREEN GRIP fitting’ the ribs to the basepipe and forming a very strong product, ie much stronger than a slip-on equivalent as shown in Figure 42. Figure 42: Shrink fit Dura-Grip screen

The screen jacket, which is the completed wire-wrap and rib assembly, is then fillet welded directly to the base-pipe or depending on metallurgies and applications - can be welded to an end-ring which is in turn welded or poxyed to the base-pipe.

‘Triangular’ x-section

‘House’ x-section Figure 43: Wrap Wire Shapes

The wrap wires are generally triangular or ‘keystone’ in cross-section and have varying dimensions and metallurgies. Typically, they are 0.090” and 0.105” deep and either 304L, 316L or Incoloy 825. The gap between the wrap wires is called the screen gauge is typically General Sand Control Information Manual External Revision 1.0 - 58

measured in thousandths of an inch. Thus a “12 ga” screen is called 12 gauge and has a 0.012” (approximately 300 microns) air gap. The open area of such a screen jacket would hence be (0.012)/(0.090 +0.012) or 12%. The smaller the gauge, generally the smaller the open area unless the wrap wire width is reduced. The wrap wire can also be trapezoidal (house-shaped) in cross-section and some operators believe that this adds significantly to the screen’s resistance to erosion. See Figure 43. Unlike most other screen manufacturers, Weatherford makes and treats its own wire and therefore maintains a large stock of raw material, see Figure 45. Weatherford can hence respond rapidly to non-standard specifications and quality controls the wrap-wires using online laser measurement as shown in Figure 44. The rib wires (sometimes called rod wires) can be circular or triangular in crosssection. For rod based screens (ie with no basepipe), the ribs are of course thicker and more numerous to provide the required mechanical strengths.

Figure 44: Quality control of wire forming process

Wire-wrap screens are typically used to control coarse and very well-sorted sand grains. They are sometimes used in “stand-alone” applications, for example in Norway where the sands are unusually large and well sorted in some fields. Generally, they are used behind a gravel pack and are sized/selected to keep the gravel in place. The gravel is of course much

larger and much better sorted than formation sand grains. The gravel, packed into the annulus between the screen and the formation, actually controls the formation sands and the wire-wrap screen simply keeps the gravel in place. Figure 45: Wire forming and inventory General Sand Control Information Manual External Revision 1.0 - 59

Figure 46: 88 Spindle drilling machine (44ft jts)

Wire-Wrap Screens

FREE FLOW

HOUSTON WELD SLIP-ON

DURA GRIP

Figure 47: Wire-wrap screen types

There are three basic types of wire-wrap screens available from Weatherford illustrated above in Figure 47. All use the wire-wrap jacket with triangular or house shaped wrap wires. As Weatherford stocks raw material and forms its own wire shapes, a very wide range of shapes and size wires can be used. The wrap wire can be house or triangular in profile. The height and width can be varied to suit any particular application, in terms of open area and strength. The curvature at the edges is created by the tungsten carbide dye used to form the wire and can also be adjusted to suit a clients particular request. Some companies require very acute angles and some do not specify the curvature at all. The standard Weatherford curvature is selected to promote the formation of a stable permeable sand filter cake. Width: Typically 0.070” or 0.090”

Height: Typically 0.105” or 0.140”

Figure 48: Wrap-wire profile General Sand Control Information Manual External Revision 1.0 - 60

The standard tolerance on the screen gauge is +0.001” and –0.002”, ie plus 1 thou and minus 2 thousandths of an inch. Erosional tests on house shaped wires and normal wedge shaped are frankly inconclusive. The wedge shape did exhibit more specific erosion, ie metal loss, but the affect on gauge in comparison with the house shaped wire was not significant. The choice of house or wedge shaped wire is therefore a matter of client preference. The rib wires (strapped longitudinally along the base-pipe) also are available in different sizes and shapes. Standard rib wires are round wires, circular in cross-section with a diameter of typically 0.105”. Rib wires are available of course in triangular cross-section also. The number of rib wires is standardised but can be increased or decreased as required. Too many rib wires can decrease in-flow area and add unnecessarily to the cost of manufacture. Too few rib wires will make a fragile jacket. The number and size of rib wires is very important in Free-Flow type screens where they contribute entirely to the tensile and compressional strength of the screen. The weld strength of a 0.090” x 0.140” wrap wire to a 0.105” rib wire is 448 lbf. The industry standard is about 350 lbf. Larger rib wires and adjustments in weld voltage and feed-rates can increase this weld strength still further.

Houston-Weld® Screens The screen jacket or slip-on screen is manufactured to exact specifications by diameter, length, gauge, and strength. Selecting the correct profile wire and support rods and feeding them into a dedicated wrapping machine does this. On this electronically controlled equipment, the screen is produced by cylindrically wrapping while fusion welding the profile wire onto a number of support rods at each intersection. The synchronised feeding of support rod with profile wire wrapping results in a uniform cylinder-like, continuous, and constant gauge screen. The base-pipe is selected to API specifications by size, grade, and weight for each application. The pipe is then perforated, leaving blank areas on each end for make-up and handling. The screen jacket is then slipped over the perforated base pipe. The two components are then joined together by end welds. Houston-Weld screens are essentially slip-on screens and are manufactured in a similar process to most other wire-wrap screens available. Consequently, their performance and ratings are also similar. Slip-on screens offer certain advantages in terms of cost and delivery. Often, if a rush order is received, the wire-wrap jackets can be manufactured before the base-pipe has been procured and perforated. For this reason, Weatherford has invested in fast perforating machines (Range III 44ft joints can be perforated in a single chucking, see Figure 46) and maintains a substantial inventory of base pipe and wire-stock.

Dura-Grip® Screens Dura-Grip (DG) screens are manufactured with the rib wire in place on the base-pipe during jacket manufacture. This has the effect of shrink-wrapping the screen jacket to the perforated base-pipe - a process similar to winding a rope around your hand, the binding force keeps increasing with each wrap. Consequently, even the minimum specification DuraGrip screens are among the very strongest wire-wrap screens available. A table presenting the standard dimensional data of DG screens is provided below. General Sand Control Information Manual External Revision 1.0 - 61

Holes Size (In)

Open Area Of Holes (In2/Ft)

Approx OD Dura-Grip

3/8

3.98

1.715

5.56

8.00

12.32 1.815 5.59

8.05

12.44

1.66

1.38

2.3

48

3/8

5.30

2.060

6.68

9.61

14.79 2.160 6.65

9.58

14.81

1.900 1.610

2.75

60

3/8

6.63

2.300

7.46

10.73 16.52 2.400 7.39 10.64 16.45

2.063 1.751

3.25

72

3/8

7.95

2.463

7.99

11.49 17.69 2.563 7.89 11.37 17.57

2.375 1.995

4.6

84

3/8

9.28

2.775

9.00

12.94 19.93 2.875 8.85 12.75 19.71

2.875 2.441

6.4

96

3/8

10.60 3.275 10.62 15.27 23.52 3.375 10.39 14.97 23.13

3.500 2.992

9.2

108

3/8

11.93 3.900 12.65 18.19 28.01 4.000 12.31 17.74 27.42

4.000 3.548

9.5

144

3/8

15.90 4.400 14.27 20.52 31.60 4.500 13.85 19.96 30.84

4- 4.500 4.000 1/2"

11.6

168

3/8

18.56 4.900 15.89 22.85 35.19 5.000 15.39 22.18 34.27

5.000 4.408

15

180

3/8

19.88 5.400 17.51 25.18 38.78 5.500 16.93 24.39 37.70

5- 5.500 4.892 1/2" 65/8" 6.625 5.921

17

192

3/8

21.21 5.900 19.13 27.52 42.37 6.000 18.46 26.61 41.13

24

204

3/8

22.53 7.025 22.78 32.76 50.45 7.125 21.93 31.60 48.84

26

216

3/8

23.86 7.400 24.00 34.51 53.14 7.500 23.08 33.26 51.41

26.4

228

3/8

25.18 8.025 26.02 37.43 57.63 8.125 25.00 36.04 55.69

32

240

3/8

26.51 9.025 29.27 42.09 64.81 9.125 28.08 40.47 62.55

47

252

3/8

27.83 10.03 32.51 46.75 71.99 10.13 31.16 44.91 69.40

11/4" 11/2" 21/16" 23/8" 27/8" 31/2" 4"

5"

7"

7.000 6.273

7- 7.625 6.969 5/8" 8- 8.625 7.921 5/8" 95/8" 9.625 8.681

Dura Grip Open Area (In2/Ft)

.008" Slot

.012" Slot

.020" Slot

Approx OD Dura-Grip Plus

Holes Per Foot 36

Pipe ID (In)

1.7

1"

Pipe OD (In)

1.315 1.049

Screen Size (In)

Pipe Wt/Ft

Dura-Grip Screens Dura-Grip Plus Screen Open Area (In2/Ft)

.008" .012" Slot Slot

.020" Slot

Table 10: Dura-Grip & Dura-Grip Plus standard dimensions

Note that Dura-Grip Plus refers to a Dura-Grip screen made with house-shaped wrap wires.

Base-Pipe Friction Because the rib wires are in close contact with the base-pipe, a frictional force is evident whenever the base-pipe and rib wires are subject to differential stresses. For example, if the wire-wrap jacket is pushed along the pipe axis relative to the base-pipe, on a 4” screen a force equivalent to 25,000 lbf per foot of screen is required to move the jacket.


Figure 49: Tensile testing of wire-wrap screens

This high frictional force helps the DG screen to maintain its gauge even after extreme stresses (eg torsion, tension, compression) have been applied. In general terms, as long as the stresses are within the elastic limit of the pipe & jacket assembly and as long as the screen assembly is left in a relatively unstressed state, the screen gauge can be expected to have returned to within tolerance. Testing indicates that DG screens maintain approximately 90% of the unperforated base-pipe strength as shown in Figure 49.

Thermal Applications At elevated temperatures and especially in thermal cycling applications, a number of potential issues arise with wire-wrap screens. The end-weld of the jacket to the base-pipe requires to be qualified for the application and also attention to the screen gauge is required.

Screen Size 2-7/8 4 5-1/2

OD (in.) ID (in.) OD (in.) ID (in.) OD (in.) ID (in.)

Diameters at 700 F 3.243 2.456 4.404 3.591 5.92 4.924

at 70 F 3.228 2.441 4.361 3.548 5.888 4.892

Diametric Difference in inches 0.015 0.015 0.043 0.043 0.032 0.032

Table 11: WW Screen diameter change with temperature


The forces on the screen and base-pipe during thermal cycling can be considerable. Tests indicate that heat cycling concerns (to 700°F) are not applicable to DG end welds as the base pipe frictional forces distribute the thermal loads along the base-pipe. If a slip-on screen is used in these cases, special floating end-rings will be required, special weld procedures and also the screen gauge may be affected. Further tests indicate that there is no appreciable change in DG gauge over 70 to 675°F. However, it should be noted that the metals will undergo yield strength degradation at these high temperatures (about 20% at 600°F for example) and their safe application limits must be reduced accordingly. The three factors contributing to gauge alteration at high temperatures are •

Base pipe axial elongation

•

Wrap wire diameter thermal expansion

•

Base pipe expansion

Figure 50: Poisson effect of base pipe expansion

At 700°F, a base pipe will expand 0.0005” (ie within tolerance) over the gauge. The diameter thermal expansion of the wrap-wire has a negligible effect on the screen gauge. Finally, the effect of Poisson thinning of the wrap wire was found to be less than 0.0001” and is also hence negligible.

Summary of Dura-Grip Features •

Base-pipe is perforated in up to 44ft lengths in a single chucking

•

Base-pipe is cleaned, deburred and prepared for wrapping on high speed lathes

•

Wedge wire is formed from a large raw stock wire inventory to a wide range of shapes and sizes. Weatherford can therefore respond very quickly to customer requirements.

•

Wire-wrap jackets are wrapped directly on to the base pipe. This results in a screen which is stronger and more robust than competitor products.

•

Screen is available in a wide range of metallurgies and base-pipe strengths.


Free-Flow™ Screens The Houston Free-Flow™ screen provides the maximum inlet area of any wire-wrap based well screen design. This screen is versatile and can be adapted to many industrial functions. The strength and durability of this type of screen comes from the shape and mass of the wrap wire and rods combined with the efficiency of the welding techniques used in manufacturing. The special trapezoidal shaped wire is drawn from carefully specified material, double-annealed and roll formed to precise desired dimensions. The wire is then spiral wrapped around the longitudinal rods of the same material and resistance welded at each point of contact. Figure 51: Free Flow Screen

Summary of Free-Flow Key Features •

Of like material to avoid electrolytic corrosion

•

Cross-sectional shapes selected to provide maximum open area with sufficient strength

•

Welded at each junction with support rod

•

Inwardly widening openings assure non-clogging, selfcleaning slot configuration

•

Continuous slot construction provides maximum open area which reduces entrance velocity and increased hydraulic efficiency

•

In-plant design and manufacturing of wire shapes ensures tolerances within rigid specifications.

•

Fittings bevelled to ensure complete weld material fill for ultimate strength

•

All standard and custom made end fittings rigidly secured to screen

•

End fittings can be made of different material than the screen body. Figure 52: Free flow screen section


Pre-Pack Screens

PERMA BOND

MICRO PAK

Figure 53: Pre-pack configurations

MUNI PAK

EXACT PAK

Perma-Bond® Perma-Bond combines an internal Dura-Grip screen with an outer screen jacket. The annular space between the screens is packed with appropriate size sand or proppant, while industrial vibration system insures proper compactness. The pack material can be either curable phenolic resin coated or non-resin coated. The Perma-Bond screen was originally designed as an alternative to gravel packs. It is used primarily as a stand alone sand control device. Perma-Bond screens have also been used effectively in wells with marginal production potential where gravel packing has been deemed uneconomical.

Micro-Pak® Micro-Pak is manufactured in much the same manner as Perma-Bond. Its unique design makes it one of the most versatile screens as it provides both a similar OD and a larger ID than conventional pre-packed screens. Micro-Pak is an excellent choice in advanced sand control techniques such as high-rate water packs and frac packs to provide insurance against voids in the gravel pack. It also minimises the chances of erosion and leak-off problems during the sand placement part of these techniques. Micro-Pak is a proven product in horizontal wells and thru-tubing applications world-wide.

Protecto-Pak® Protecto-Pak consists of a perforated outer shroud and a Dura-Grip inner screen encapsulating a layer of pre-cured phenolic resin-coated sand or proppant. Protecto-Pak was designed primarily for wells with damaged casing or where a casing window has been cut and placement of a wire wrapped screen could result in damage. This screen product has also been used successfully in horizontal wells and thru-tubing applications.


Exact-Pak® & Muni-Pak™ Screens Large diameter water wells have been gravel packed as a technique to provide sand control. This technique remained largely unchanged until the introduction of the Exact-Pak and MuniPak screens. Eliminating the need for the conventional gravel packing, this thin pre-pack design allows for closer contact between the inside of the screen and the aquifer, which results in better well efficiency. This unique design guarantees positive placement of gravel pack with no bridges or voids.

Pre-Pack Screen Proppant The main concern regarding pre-packed screens is their susceptibility to plugging with completion, drill-in fluids and muds. To address this issue, Weatherford uses Carbolite proppant as the main pack media as opposed to resieved sand. Carbolite advantages include larger pore throats and more precise sorting, which improve the global permeability of the system. Comparison tests show that resin coated Carbolite proppant allows 120% more fluid volume to pass through than resin coated sand. Also the sphericity of the Carbolite virtually eliminates the bridging concerns during the packing process of the screen. Bend tests showed Micro-Pak screens packed with the resin coated Carbolite to be able to withstand up to 40 degree per hundred bend radius with no damage to the pack or wire wrap. Since acid stimulation treatments are a standard in the Gulf of Mexico, a resin coated proppant is recommended. Phenolic resin coating of the proppant will give best results if HF acid stimulation is required in the life of the well. Figure 54 & Figure 55 shows the difference in sphericity and uniformity between the natural gravel and the man-made Carbolite proppant. Figure 54: Resin coated gravel

Figure 55: Resin coated proppant (Carbolite)

Another phenomenon that operators are often concerned with is the difference between cured and uncured resin screens and how this affects screen permeability. When sand is resin coated and cured, due to the less precise sorting and non-sphericity, the pack tended to be tighter and less porous. The resin when cured was thought to blind off some of the pore throats and this would affect the screen permeability. For ceramic proppants, this is not an issue as, from inspection of Figure 56, the difference is not significant at flow rates that the screen is likely to see, ie less than 700 stb/ft. Note that for chemical compatibility reasons, it is advisable to run resin coating on the proppant and if required a pre-cured resin coated proppant can be supplied. Micro-Pak screen can be packed with curable resin coated Carbolite, pre-cured resin coated Carbolite, or non-resin coated Carbolite.


Performance of 2 7/8" Micro-Pak w/ 20/40 Carbolite 2

Pressure drop/ft (psi/ft)

1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0

200

400

600

800

1000

1200

BBL/day/ft Cured Micro-Pak

Uncured Micro-Pak

Figure 56: Comparison between cured and uncured proppant permeability

Weatherford manufactures 40ft pre-pack screen jackets without a centre break. The outer jacket is installed on the screen and raised to the upright position. The proppant is then introduced into the screen annulus and allowed to settle under agitation from industrial sized vibrators. As the proppant is very spherical, it gives much less friction and hence can flow and pack properly over a long length. See Figure 57. Once the proppant is in place, the screen is the welded closed and prepared for the curing process. This process uses steam which is pumped inside the screen. Conventional curing is performed in convection ovens and because the heat is transferred by air, the process is less consistent and reliable. Steam conducts the heat more efficiently and also flushes out any debris/loose fine grains. See Figure 58. Figure 57: Pre-pack tower


Figure 58: Steam curing process

Weatherford Pre-Packs – Key features •

Patented Dura-Grip wrapping process to adhere the inner screen to the base pipe for added strength

•

Custom-designed sand packing system to centralise the annulus during the fill cycle

•

Industrial vibrating system to prevent internal sand bridging and ensure an even, consistent fill and compaction

•

Multiple wire gauge and filter media options including resieved and phenolic resin coated media

•

Steam thermal curing system to ensure a consistent bond for resin coated media for the entire joint

•

Only company capable of producing custom lengths to 39’ of screen on a 40’ joint without a centre break.


1" 11/4" 11/2" 21/16" 23/8" 27/8" 31/2" 4" 41/2" 5" 51/2" 65/8" 7" 75/8" 85/8" 95/8"

Radial Pack (In)

Approx. Screen OD (In)

Open Area Of Holes (In2/Ft)

Hole Size (In)

Holes Per Foot

Pipe Wt/Ft

Pipe ID (In)

Pipe OD (In)

Screen Size (In)

Micro-Pak Screens

Inner Screen Open Area (In2/Ft)

.008" Slot

.012" Slot

.020" Slot

Outer Screen Open Area (In2/Ft)

.008" Slot

.012" Slot

.020" Slot

1.315 1.049

1.7

36

3/8

3.98

2.011 0.228 6.90

1.66

2.3

48

3/8

5.30

2.356 0.228 8.43 11.94 17.91 9.11 13.00 19.74

1.900 1.610 2.75

60

3/8

6.63

2.596 0.228 9.49 13.45 20.17 10.04 14.32 21.75

2.063 1.751 3.25

72

3/8

7.95

2.759 0.228 10.21 14.47 21.71 10.67 15.22 23.11

2.375 1.995

4.6

84

3/8

9.28

3.071 0.228 11.60 16.43 24.65 11.87 16.94 25.73

2.875 2.441

6.4

96

3/8 10.60 3.571 0.228 13.82 19.57 29.36 13.81 19.70 29.92

3.500 2.992

9.2

108

3/8 11.93 4.196 0.228 16.59 23.50 35.25 16.22 23.15 35.15

4.000 3.548

9.5

144

3/8 15.90 4.696 0.228 18.81 26.64 39.96 18.16 25.91 39.34

4.500 4.000 11.6

168

3/8 18.56 5.196 0.228 21.02 29.78 44.67 20.09 28.67 43.53

5.000 4.408

15

180

3/8 19.88 5.696 0.228 23.24 32.92 49.39 22.02 31.42 47.72

5.500 4.892

17

192

3/8 21.21 6.196 0.228 25.46 36.07 54.10 23.96 34.18 51.91

6.625 5.921

24

204

3/8 22.53 7.321 0.228 30.45 43.13 64.70 28.31 40.39 61.33

7.000 6.273

26

216

3/8 23.86 7.696 0.228 32.11 45.49 68.24 29.76 42.46 64.47

7.625 6.969 26.4

228

3/8 25.18 8.321 0.228 34.88 49.42 74.13 32.17 45.91 69.71

8.625 7.921

32

240

3/8 26.51 9.321 0.228 39.32 55.70 83.55 36.04 51.42 78.09

9.625 8.681

47

252

3/8 27.83 10.321 0.228 43.75 61.98 92.98 39.91 56.94 86.47

1.38

9.77 14.66 7.78 11.09 16.85

Table 12: Micro-Pak standard dimensions

Input numbers are nominal.


Zonal Isolation

Figure 59: Isolation Sleeve

Weatherford manufactures and provides wire-wrap screens slipped over and welded onto sliding sleeves. These are used to select or shut-off production zones in a multiple zone completion. Typical assembly dimensions are provided in Table 13.

Figure 60: Screened isolation sleeve

Zone Isolation Screen Assemblies Slip On Screens Size 2-1/16" 2-3/8" 2-7/8" 3-1/2"

Sliding Sleeve OD 2.190" 2.75" 3.166" 4.10"

Screen ID 2.20" 2.90" 3.18" 4.20"

Screen OD 2.58" 3.30" 3.55" 4.576"

Micro-Pak Screens Size 2-1/16" 2-3/8" 2-7/8" 3-1/2"

Sliding Sleeve OD 2.190" 2.75" 3.166" 4.10"

Screen ID 2.20" 2.80" 3.18" 4.20"

Screen OD 2.95" 3.58" 4.00" 5.00"

Table 13: Typical isolation sleeve dimensions

The ID and OD of screens are the same when not using sliding sleeves to allow communication between the screen ID and the outer non-perforated pipe.


Pre-pack & Wire-wrap Selection Criteria for Internal Gravel Packs This guideline, developed for the Gulf of Mexico, addresses the requirement of conventional slurry packs as well as high rate water packs and fracture pack type cased hole completions. Each presents certain challenges, with pressure pumping in particular exerting enormous forces on the screen and blank pipe assembly during the completion process. Dura-Grip has functioned well in all of the above completion techniques when certain factors such as pump rate, return rate and the absence of formation fines are closely monitored. A lack of control in any of the above noted areas can result in an erosional failure either during pumping or in the early production life of the well. Because of these reasons, Micro-Pak screens are increasingly used in these applications. The guidelines that follow deal primarily with cased hole completions. Openhole completions such as those required to complete horizontal wells and thru-tubing applications present different challenges and have been discussed already in the subsection on Selection Process on Page 49. •

Any gravel pack job pumped at a rate greater than 5 bpm should use a Micro-Pak screen.

•

Micro-Pak pack media will match or be larger than the gravel.

•

Slot size of the screen will correspond to the media being used to pack the well with. !

0.006 gauge with 50/70 or 40/60 gravel pack sand

!

0.008 gauge with 40/60 gravel pack sand, 30/50 proppant, or 20/40 proppant

!

0.012 gauge with 20/40 gravel pack sand or proppant also with 16/30 proppant

!

0.020 gauge with 12/20 gravel pack sand

•

Metallurgy of the wire wrap and base pipe will be determined by well conditions

•

Standard base pipe will be 80kpsi grade with 110kpsi blank pipe. The blank pipe will have a minimum collapse resistance of 10,000psi in all sizes

•

Dura-Grip screen can be used on gravel pack jobs where the rate of pumping does not exceed 5 bpm

•

Micro-Pak and Dura-Grip screens are available in standard keystone shaped or heavyduty "house shaped" wrap wire

Screen OD Sizing Guidelines •

5" and 5 1/2" casing sizes - 2 3/8" Dura-Grip or Micro-Pak

•

7" casing - 3 1/2" or 4" Dura-Grip or Micro-Pak

•

7 5/8" casing - 4" or 4 1/2" Dura-Grip or Micro-Pak

•

9 5/8" casing - 5" or 5 1/2" Dura-Grip or Micro-Pak.

A minimum annular radial clearance of 3/4" between the casing ID and the screen OD is the optimum for obtaining a good gravel pack, although sometimes 1” radial clearance is recommended depending on the length of the interval to be packed. Screen and blank used in cased hole completions are typically centralised every 15-20 feet depending on joint length with 4 blade type weld-on centralisers. The OD of the centralisers is 1/8" less than the drift ID of the casing.


Wire-Wrap Screens Safe Application Limits The following table provides the safe application limits based on physical testing and interpolate to different screen sizes. Note that a 20% safety factor has been applied to the yield values. Note that repetitive stresses & strains will reduce these limits. Note also that combination loading will also reduce these limits. Although tensile ratings are relatively straightforward to test and calculate, compressional ratings are not. Most steels are stronger in compression than tension but because of buckling, it is not possible to provide compressional data without knowledge of the completion and supporting tubular dimensional data. Even then, any calculations are likely to be highly approximate.

DURA-GRIP Size (in) 2-3/8 2-7/8 3-1/2 4 4-1/2 5 5-1/2 6-5/8 7

Tensile (lbf) 109,600 157,360

283,920

Collapse (psi) 8,835 8,370 7,890 4,940 4,915 4,890 4,415 4,160

Burst (psi) Burst (psi) .006 slot .010 slot

Pipe Wt (lbm/ft)

Holes/ft

4.6 6.4 9.2 9.5 11.6 15 17 24 26

84 96 108 144 168 180 192 204 216

4.6 6.4 9.2 9.5 11.6 15 17 24 26

84 96 108 144 168 180 192 204 216

9,000+

2,300

1,600

MICRO-PAK 2-3/8 2-7/8 3-1/2 4 4-1/2 5 5-1/2 6-5/8 7

109,600 157,360

283,920

8,835 8,370 7,890 4,940 4,915 4,890 4,415 4,160

9,000+

7,400

5,400

5,000

Table 14: Wire-wrap safe application limits

The bend angle is normally limited to a maximum of 40°/100ft but varies with screen size and type. Typically, the maximum torque is limited by the threaded couplings selected, but this again varies with coupling and screen size and type. Consult customer services to obtain the applicable limits.


6. Stratapac® Screens Weatherford Completion Systems Stratapac® Screens are currently installed in over 800 wells world-wide and in very many different applications ranging from thru-tubing remedial to extended reach horizontal wells. An installation summary is available which details the fields, lengths, type of screen and application type. The first Stratapac screens were introduced to service the demands of Operators in the Gulf of Mexico for robust and rugged screens. The screen consists of an outer protective steel cage (sometimes called a shroud) which covers the internal filtration media. The cage and filtration media – called the screen jacket – is welded onto a machine perforated base-pipe via steel rings welded to each end of the screen jacket. Stratapac Screens represented a major departure from conventional screen technology when they were first introduced in 1994 and again in 1996 with the Stratapac PMF media and they received a number of awards for innovation and new technology in the Oil & Gas industry. Figure 61: Stratapac screen (Range III) with solid rotating centralisers installed

PMM® (Porous Metal Media) is a fixed pore filtration medium with an engineered pore throat size distribution. It provides the finest (60 µm) sand control available in metal media. This is the original media introduced with Stratapac screens in 1994. Porosity is 52% by helium displacement. When introduced, it was designed to replace 40/60 pre-pack screens and there is still no equivalent all-metal screen currently available.

Figure 62: SEM of Stratapac PMM medium

PMF-IITM (Porous Metal Fibre) introduced in 1996 provides a much coarser medium and is available in 125 µm and 200µm sizes for sand control. PMF-II is an adaptation of Pall Corporation’s PMF media. The fibres are sintered within two layers of square weave mesh. PMF-II is hence a fixed pore filtration medium with an engineered pore throat size distribution. The measured porosity is 68 to General Sand Control Information Manual External Revision 1.0 - 74

72% (depending on the media grade – PMF2040 is 68% and PMF1220 is 72%). The Stratapac PMF screens were designed to emulate pre-pack screens in filtration efficiency and there remains no other fixed pore (sintered) media available with such a high porosity to date. The importance of media porosity is shown and discussed in the various comparison tests with competitor screens in the subsection on Comparison Tests.

Figure 63: SEM of Stratapac PMF-II media

Stratapac Construction Stratapac screen media are available in the three main filtration ratings and also in two media metallurgies. Other screen variations are largely determined by the base pipe selected (length, diameter, metallurgy, strength). Customers can request Stratapac screens to be manufactured with a Dutch twill weave media or with wire-wrap outer or inner cages. Stratapac down-hole screens are constructed from inside to outside of the following independent layers: • •

A perforated base pipe (grade as required). An inner layer of square weave woven wire mesh for support and drainage.

Two layers of PMF-II 1220 filter media or four layers of PMM filter media. Each layer is welded independently and the weld seams are offset from one another by 120°. • An outer layer of square weave wire mesh for back pressure support and drainage completes the screen media construction. • A perforated stainless steel outer cage for protection during handling and running in the well bore. Various grades and thicknesses are available. Base-pipe metallurgy L/N80 with screen media and meshes in either 316L stainless steel or Alloy 20 (equivalent to Incoloy 825), depending on bore-hole conditions and whether the screen must be acidised or not. The outer cage is normally of a slightly lower metallurgy (304L minimum) as its long term resistance to corrosion is not perceived to be critical since it is designed mainly to protect the screen medium during deployment. The base pipe metallurgy can be selected as required from J55 to super-duplex 28Cr, etc.

•

Pipe Length and Sizes Connections, thread protectors, markings, documentation, packaging, handling clearances, joint lengths, screen length, base pipe OD and ID, screen OD details should be specified at time of order.


Acid Backwash and Flushing The all-metal construction allows the Stratapac screens to be flushed and washed with relatively high concentration acid breakers7. In addition, the Stratapac screen has excellent back pressure support and so can withstand cleaning and back flushing operations well. Please refer to the handling guidelines for reverse pressure limitations and cyclic service8.

Minimised Screen Thickness The standard Stratapac screen is about 1/3rd inch thick, and the increase in diameter from the base pipe is therefore only about 0.65 inches9. The use of Excluder10, wedge wire or prepack can increase screen diameter by as much as 1.5 inches. In many instances, this allows the Stratapac screen to use a larger (and also even stronger) base pipe. Use of a larger base pipe can also result in higher flow-rates and hence increased production. An increased ID base pipe also provides a greater number of options to run service tools during coiled tubing and work-over operations. Alternatively, the Stratapac screen OD is smaller than other comparable screens and thus will experience less deployment problems in short radius turns, horizontal well sections or casing windows11 (see below).

Crush Test The original Stratapac Screen equipped with PMM media had been subjected to an extensive series of mechanical strength tests, and the screen’s construction was determined to meet or exceed all requirements for well service. The PMF-II media is constructed with a different substrate mesh than the PMM and two layers of PMF-II are used in the screen vs. four PMM layers so, additional tests were performed to validate the screen’s mechanical strength with the new media. To accomplish this a crush test was conducted on the screen and the sand retention was evaluated before and after crushing, see Figure 64 below.

Figure 64: Crush samples (left) and apparatus (right)

7 See “Material Selection and Recommendations for Protection of Stratapac Screen against Corrosion” (SLS Report # 5132) 8 See “General Handling and Running Guidelines” 9 See attached Stratapac and Stratacoil Brochure (Weatherford ‘00) 10 Trade mark of Baker Oil Tools 11 See “Bending Test of Stratapac and Wire-Wrapped screens for Shell Offshore, New Orleans, LA” (SLS Report # 5212)


Results Table 15 lists the total suspended solids obtained from the tests. Sample

Sand Retained on Mesh (g)

Upstream Downstream, Intact Screen Downstream, Crushed Screen

47.24 0.24 0.26

Table 15: Screen crush test - total suspended solids

Damage Resistance Testing showed that the Stratapac down-hole screen can be completely crushed at the welded end-ring or in the screen centre and still maintain sand retention capabilities. Prepacked and wire wrapped screen allow the passage of formation sand when deformed which erodes and eventually damages completion equipment and surface facilities. Third party testing to determine tensile strength showed elongation of the Stratapac down-hole screen to two inches with no failure – this was the limitation of the test apparatus – whereas prepacked screens failed at 0.39 inches of elongation. This indicates that the Stratapac downhole screen will not fail prematurely when run in short radius, highly deviated or horizontal wells. Also, maintaining complete screen integrity will ensure an even flow distribution over the entire length of the Stratapac screen and hence minimise local screen erosion. If other screens are damaged, sand-loaded fluid flow is concentrated through the damaged areas (so called “hot spots”) which greatly increases local erosion rates and hence causes premature screen failure12 as sand is eventually produced.

High Burst Pressure Applications For certain applications including fracture packs, operators sometimes require a screen with a higher burst rating. This would be necessary for example if the screen became plugged with LCM material from the inside during the completion and the differential pressure across the screen could not be controlled within certain operational limits. In these situations and depending on the overall differential pressure expected, variations to the standard Stratapac screen design are available. The standard Stratapac screen burst rating is derived from the yield point of the outer cage. When the outer cage begins to yield (ie move) under the reverse pressure, the media would be expected to start to stretch elastically at first. The media is more elastic than the cage and base-pipe, but due to the difficulty in predicting the exact failure pressure (ie the pressure at which the media is stretched plastically and this effect on sand retention is significant), the yield point of the outer cage is selected as the burst pressure rating. Although, this rating incorporates a significant safety margin (50%), caution should be used in case of pressure cycles. Field proven high burst pressure Stratapac screen designs are available. Please contact Weatherford Completion Systems for further details.

12 See “Accelerated Erosion Tests on Stratapac and Baker Hughes Inteq Excluder Sand Control Screens” (SLS Report # 6338)


Certain competitor screen designs involve crimping the media rather than welding along the length of the sand screen. This leads to the possibility of seal by-pass and poor screen performance in reverse pressure situations.

Bypassing Seal

Welded Seal Figure 65: Welded vs non-welded seals

Also, some screens have non-welded end-rings which fix the screen jacket to the base-pipe. The seal in this instance is sometimes provided by an elastomer. Again, with time this will become a potential failure point. Stratapac screens have welded end-rings applied under stringent QC conditions to prevent this potential problem.

No Bypass

Figure 66: Welded end-ring seal

Bypass

Stratapac screens are multi-layered and each layer is welded longitudinally along the length of the screen. The screen is then rotated through 120 degrees and the next layer is welded. Each weld is therefore offset from one another by 120 degrees. In the event of a poor weld, the Stratapac screen provides no direct fluid flow path. In addition, each layer is independent as a perforated bronze “chill” strip inserted behind each weld keeps the weld from penetrating to the layer below. Some multi-layer screens have only one weld for all layers (Figure 67). In the event of a weld defect, this could lead to the opening of a direct flow channel through the screen and hence loss of sand control.

Figure 67: Longitudinal media welds


Standard Design Stratapac & Stratacoil Dimensions Typical dimensions for a standard design Stratapac screens built on API base pipe are presented below in Table 16.

OD (in)

Nom Wt1 (lbm/ft)

Screen ID (in)

Screen OD2 [±0.06] (in)

Total Screen Weight3 (lbm/ft)

Screen Area per Joint3 (ft2)

2.375

4.6

2.00

2.98

7.89

19.0

2.875

6.4

2.44

3.48

10.15

22.4

3.5

9.2

2.99

4.11

13.5

26.7

4.0

13.2

3.34

4.61

18.1

30.0

4.5

12.6

3.96

5.12

17.9

33.5

5.0

15.0

4.41

5.63

20.8

36.8

5.5

17.0

4.89

6.13

23.2

40.3

6.625

24.0

5.92

7.27

31.1

47.9

7

26.0

6.28

7.65

32.9

50.5

Table 16: Standard Stratapac screen dimensions 1

API Base Pipe – typical values used. Customer can select alternative base pipe wts. Screen OD: Maximum outer diameter may change depending on the type of connection selected. 3 Screen weight per foot and area per joint is dependent on overall pipe length. Values shown are for 31ft pipe. 2

Typical dimensions for standard design Stratacoil screens are presented below in Table 17.

OD (in)

Nom Wt (lbm/ft)

Screen ID (in)

Screen OD1 [±0.03] (in)

Coupling OD3 (in)

Screen Area per Joint (ft2)

1.315

2.65

0.95

1.64

1.66

3.9

1.66

3.36

1.29

1.98

2.054

4.8

1.90

3.84

1.5

2.19

2.20

5.4

2.063

4.14

1.61

2.30

2.50

5.8

Table 17: Standard Stratacoil screen dimensions 1

CAUTION: Maximum outer diameter may change depending on the type of connection selected. See Coupling.


Safe Application Limits As Stratapac can withstand minor impacts and dents, it can be handled in a similar fashion to casing and tubing, and can be racked back in the derrick as required. Procedures for the running and handling of the screens are reviewed prior to installation. Please note that the limits noted in the published literature are our recommended application limits and incorporate a safety factor. This infers that the limits may be more conservative than that recommended by competitor manufacturers who often state failure limits. Note that these limits are stated only for standard build Range II (31ft) screens. Special build screens can be provided for example for increased burst ratings and high-flow or thermal cycling applications, etc. Table 18 lists the suggested safe application limits for Stratacoil Screen. Suggested safe application limits for the standard Stratapac Screens are given Table 19. Suggested safe application limits for Hi-Flow Stratapac Screen (base-pipe holes on 1.2" pitch centres) are given in Table 20.

Nominal Size 1.315 1.66 1.9 2.06

Maximum Tensile 2 Load (Lbf) 9,380 11,950 13,604 14,450

Maximum Torsional Load (Ft3 Lbf) 287 461 584 668

Weight 4 (Lbm-Ft) 2.65 3.36 3.84 4.14

Maximum Crush Delta-P (psid) 1,800 1,500 1,200 1,000

Maximum Burst Delta5 P (psid) 1,360 1,100 990 910

Base-pipe Thickness (in/#/ft) .125 .125 .125 .125

1

Table 18 : Standard Stratacoil screen safe application limits

Nominal Size 2.375 2.875 3.5 4.0 4.5 5.0 5.5 6.625 7.0

Maximum Tensile Load 2 (Lbf) 77,200 103,800 145,300 206,000 204,700 244,800 275,500 378,700 414,400

Maximum Torsional Load (Ft3 Lbf) 2,090 3,600 6,300 10,500 12,000 16,200 20,500 34,900 40,400

Weight 4 (Lbm-Ft) 7.9 10.2 13.5 18.1 18.1 20.8 23.2 31.1 32.9

Maximum Crush Delta-P (psid) 9,100 8,700 8,500 7,500 6,800 6,700 6,100 5,800 6,700

Maximum Burst Delta-P 5 (psid) 1,080 910 760 680 600 550 500 420 320

1

Table 19 : Standard Stratapac screen safe application limits 1

All calculations are based on 80 Ksi minimum yield strength material @ 70F Screen body only; reduce as appropriate for threaded connections 3 Static loads - multiply by .50 for dynamic applications 4 Based on standard Range II Stratapac screen, no couplings or centralisers 5 Outer cage only, static applications; needs to be reduced for cyclic service. 2


Base-pipe Thickness (in)

Base-pipe Thickness (in/#/ft)

.190 .217 .254 .330 .271 .296 .304 .352 .408

4.6 6.4 9.2 13.2 12.6 15.0 17.0 24.0 29.0

Nominal Size 2.375 2.875 3.5 4.0 4.5 5.0 5.5 6.625 7.0

Maximum Tensile Load 2 (Lbf) 67,900 87,900 126,700 174.000 171,800 209,000 231,300 319,200 344,900

Maximum Torsional Load (Ft3 Lbf) 1,900 3,300 6,000 9,700 11,000 15,100 19,000 32,300 37,100

Weight 4 (Lbm-Ft) 7.9 10.2 13.5 18.1 18.1 20.8 23.2 31.1 32.9

Maximum Crush Delta-P (psid) 7,700 7,200 7,000 7,900 5,800 5,700 5,300 5,100 4,900

Maximum Burst Delta-P 5 (psid) 1,080 910 760 680 600 550 500 420 320

Base-pipe Thickness (in)

Base-pipe Thickness (in/#/ft)

.190 .217 .254 .330 .271 .296 .304 .352 .408

4.6 6.4 9.2 13.2 12.6 15.0 17.0 24.0 29.0

1

Table 20 : Hi-Flow Stratapac screen safe application limits 1

All calculations are based on 80 Ksi minimum yield strength material @ 70F Screen body only; reduce as appropriate for threaded connections 3 Static loads - multiply by .50 for dynamic applications 4 Based on standard Range II Stratapac screen, no couplings or centralisers 5 Outer cage only, static applications; needs to be reduced for cyclic service 2

Dog-Legs, Casing Windows and High Build Angles Standard sand control screens can be subject to a number of specific damage mechanisms when used in irregular bore-holes and “bending” applications: •

Localised damage to the wire and opening of the slots due to scraping against the casing or bore-hole irregularities, and subsequent loss of sand if pre-packed. • Structural damage to the screen jacket (parting of the screen jacket at the end ring due to stress accumulation in the bend). • Cracking and voiding in pre-packs. Losing pre-pack material (voids) through stretched wire-wrap gaps even when bending elastically on the wire-wrap. • Coupling/connection yield. • Permanent set or yield on the perforated base pipe (ie plastic deformation) leading to difficulties in deployment in subsequent straight bore-hole sections. • Buckling instability failure on base pipe/cage. • Weld failure at the jacket end-ring attachment to the base-pipe. In the case of high build angles or severe hole geometries, Weatherford recommends the use of Torque & Drag modelling prior to completion equipment final selection. This is offered as an additional service and can be used also to select the most appropriate centralisation system. Stratapac Screens – Bend Limits Most of the above damage risks have been eliminated or at least mitigated in the design and construction of Stratapac screens: • • •

The external cage or shroud protects the filter medium from any contact with the casing and sharp edges in the well bore. The inherent ductility of the PMM or PMF filter medium and the unique construction of Stratapac screens allow substantial deformation of the assembly without risk of shearing the filter medium or end-rings. In addition, the rugged construction of the Stratapac screens expands the range of operational loads that can be applied to the completion string. This allows “rougher treatment” during installation (screen rotation, push & pull) and hence reduces the General Sand Control Information Manual External Revision 1.0 - 81

probability of getting stuck in the hole and also screen damage from combination loads and localised stresses. There are hence only five main potential failure modes for Stratapac due to short radius wells in order of probability: • Permanent set or yield on perforated base pipe (plastic deformation) • Coupling/connection yield • Media deformation (plastic or shear) • Buckling instability failure on base pipe/cage • End-ring weld failure The coupling/connection bend limit is determined by the coupling and the thread form selected. This factor is therefore not considered in the following table as the coupling type is normally selected by the operator. Please note that in some cases this can be the determining limit on well geometry and the operator is well advised to refer to the pipe/thread manufacturer. The lowest mode of failure has been determined by engineering calculations and confirmed in tests to be always the permanent set to the perforated base pipe. Table 21 below is therefore prepared using 70% of the base-pipe minimum yield strength. This value is selected to allow for the reduction in strength due to perforations and to keep the stresses below the elastic limit of the base pipe. The base pipe is assumed to be 80ksi minimum yield in all cases. Please note that this is not a product claim and is only a recommendation since there are many other factors that may affect the limit, including combined loads and local stress concentration factors. Base Pipe Wt #/ft

No of BasePipe Holes #/ft

2.98

4.6

2.875

3.48

3.50

Nominal Screen Size (inches)

(inches)

2.375

• • • • • •

Screen OD

Minimum Average Bend Radius

Maximum Average Build Angle

Ft

M

Deg /100ft

Deg/m

22

53

16.2

108

3.5

6.4

28

64

19.6

89

2.9

4.11

9.2

34

78

23.8

73

2.4

4.50

5.12

12.6

40

100

30.6

57

1.9

5.0

5.63

15.0

46

112

34.0

51

1.7

5.50

6.13

17.0

52

123

37.4

47

1.5

6.625

7.27

24.0

64

148

45.1

39

1.3

7.00

7.65

26.0

64

156

47.6

37

1.2

Maximum OD may change depending on coupling OD Limits are based on permanent set (plastic deformation) of the Stratapac base pipe (minimum yield 80,000 psi with standard pitch base-pipe perforations. Perforation hole size is 0.375” standard). No account is made of pipe coupling and thread types. Weatherford Completion Systems refers the operator to the appropriate thread specification or proposed thread/pipe manufacturer for the connection bending limits. Note that all screen sizes can be used in short radius wells (defined as 0.5 to 1.5 degs/ft) but there is a risk of plastically bending the screen which will make running the screen further through any different sections more difficult. Standard base-pipe perforation density and pattern. These values are guidelines only. The limits require to be reduced under combination loads. Table 21: Recommended Stratapac base-pipe safe build angle application guidelines General Sand Control Information Manual External Revision 1.0 - 82

Please note that this bend limit guideline above is independent of hole size as this is the bend applied to the screen itself. Well geometry calculations (bore hole size, centralisers and screen OD) may allow the use of screen in higher hole build angles than recommended in the table above. If pipe permanent set can be ignored, the recommended safe build angle application limit for Stratapac is shown below in Table 22. From Table 22, all Stratapac screen sizes using appropriate threaded connections can be actually used in any short radius well (defined as 50 to 150 degs/100ft), but note there is a risk of plastically bending and hence permanently deforming the base-pipe. This should be allowed for in the well design. The values in Table 22 have been derived using 50% of the yield value of the media. If these values (after allowing for the safety margin) are exceeded over the build section of a hole, there is a risk of plastically deforming the media and thereby inducing a premature screen failure.

• •

Nominal Screen Size (inches)

Maximum Average Screen Jacket Build Angle* Deg/100ft

2.375 2.875 3.50 4.50 5.0 5.50 6.625 7.00

502 424 355 282 255 233 196 186

These values do not account for permanent set to the base pipe. Please use Table 21 wherever possible. Table 22: Safe build angle application limits for Stratapac screen jackets

Screen Pore Size Distribution Technology The high porosity of the PMF-II (PMF) media ensures that even with its higher particle retention efficiency, the media experiences less plugging than mono-pore sized media. In the filtration industry, this is referred to as a high “dirt holding capacity”. Based on this, PMF was selected over woven mesh media as the primary filtration medium for Stratapac and this was confirmed as appropriate by a major in-house testing programme. Generally, operators are critical of “in-house” testing (which in fairness can be very biased) and are therefore more inclined to trust third party testing or their own field experience/lab results. Consequently, we include such third party data in the subsection Comparison Tests (page 87) from independent tests by major operators and users of sand screens. The test data indicates that the PMF Stratapac provides generally better sand control over comparable multi-layer (all-metal) premium mesh screens. When the sands are mixed or heterogeneous, this difference in sand control performance is even more pronounced in favour of Stratapac.

Porosity The Stratapac® PMF media in Figure 63 is composed of fine metallic fibres sintered to a substrate mesh for high tensile strength. The fine fibres result in a highly porous media with much higher porosity than typical pre-pack material or woven wire meshes (see Figure 68). General Sand Control Information Manual External Revision 1.0 - 83

Gravel

Woven Media

PMF Media

Porosity 30%

Porosity 45%

Porosity 70%

Figure 68: Construction and porosity of non-woven media

This is because the woven media requires the weave wires to maintain the structural strength and so they cannot be reduced in diameter to increase throughput or porosity beyond a certain limit. The woven media have very regular pore throat sizes (especially sintered meshes), but note that there may be more than one size depending on the direction of particle impingement and type of weave.

Pore Size Distribution The PMF media was designed to mimic the pore size distribution of typical pre-pack gravel material. To illustrate the similarities in distribution, 180 random pores of 20/40 gravel and PMF2040 media were measured under a calibrated microscope and plotted in the histograms shown in Figure 69 (see also SLS Report 6617 for a more complete description). Comparison of the histograms show that the PMF2040 has similar pore size distribution and average pore size as 20/40 gravel, but with better uniformity and much greater density of pores due to PMF’s higher intrinsic porosity.

Frequency

20/40 GRAVEL

PMF2040

0

100

200

300

400

Microns

Figure 69: Comparison of PMF and pre-pack pore size distributions


500

Sand Retention The pore throat size distribution of PMF media emulates a pre-pack distribution and filters sand particles efficiently. The standard filtration ratings of standard Stratapac media are tabulated as follows: Media

90% Rating

Gravel Pack Equivalent Sizing

PMM

60µm

40/60

PMF-II 2040

125µm

20/40

PMF-II 1220

200µm

12/20

Table 23: Standard Stratapac media ratings

In order to be as consistent as possible between this technology and earlier gravel pack technology, the Stratapac media are commonly designated as follows: PMM4060, PMF2040 and PMF1220.

Stable Sand filter cake with PMF-II The PMF media have a broader pore throat pore size distribution than the equivalent mesh type screens. The PMF therefore catches a slightly broader distribution of impinging sand particles and hence forms a stable and permeable sand filter cake relatively quickly. The sintered construction means that the pore size is fixed and does not alter with changes in ∆p. This means that the filtration medium is not subject to continual flexing and unloading which would otherwise lead to metal fatigue and premature failure. The construction and close proximity of the drainage mesh (and to some extent the outer cage) contribute to maintaining the sand filter cake in place even with changes in flow-rate and fluid phase. It should be pointed out that with these coarser screens (100µm and above), fines can be expected to be produced especially early on in the installation’s life. If the sand filter cake is not stable, fines can be expected with every change of ∆p (well shut-ins, etc) and fluid phase change and erosion can be expected to be more of a problem. The outer drainage mesh & perforated cage provide mechanical support to the sand filter cake during its formation and increases the sand filter cake stability during multi-phase and changeable flow condition.

Screen & Media Selection Guidelines The completion method and completion fluids should be considered in order to select the right filtration media to control sand production from a producing well. If gravel packing or inserting beads between the screen and formation, the media may be designed to control the gravel as the gravel is in turn already controlling the formation sands. Sometimes, depending on an assessment of the risks involved, the screen media is sized for the formation sands even when gravel packing because the operator is not convinced that a perfect gravel pack can be assured. This is especially so in the case of long openhole horizontal completions. Using the Coberly d10 rule for poorly uniform sands can lead to unwanted sand production. Also, the sand bridges can be made up of much smaller particles than for a uniform sand and therefore may not be as stable. Thus, one screen sizing criteria is not appropriate to all sands. Therefore, a screen selection chart was devised which selects a screen pore size based on both the average sand size and uniformity coefficient.


Stratapac Media Selection Chart Using a combination of standard gravel pack and screen selection rules (Saucier, Coberly, Schwartz), as well as laboratory experiments, a chart providing simple media selection guidelines is provided in Figure 70. Qualitatively, these guidelines are explained as follows: •

For very well sorted with low uniformity coefficients (2 < Cu < 3), the recommendations follow the Coberly rule, where the screen is sized to the d10 of the sand (the d10 is extrapolated from the d50 and the Uniformity Coefficient (Cu), assuming a unimodal sand following a standard log-normal distribution). Although 90% of the sand is smaller than the d10, the high amount of sand uniformity yields rapid sand filter cake formation and effective sand control.

•

At medium Uniformity Coefficients (3 < Cu < 7), the Coberly rule leads to too much sand production, especially in an open annulus configuration or in an injector well. The Saucier rule (screen pore size = df50) is applied where the average sand size is at or greater than the average screen pore size.

•

For large Uniformity Coefficients (Cu > 7), sizing the screen according to the Saucier rule may not prevent long-term sand production. The Schwartz rule (where screen pore size = df70) is applicable for very poorly sorted sand and leads to the selection of a very fine screen that may be susceptible to fines plugging. To avoid premature plugging silt and clays (particles less than 44 µm) should be less than 20wt%. If formation fines are greater than 20wt%, a gravel pack is recommended to lock formation sand in place, and provide a barrier to sand migration as far away from the well as possible to reduce fluid velocity.

Uniformity Coefficient (D40/D90)

10 9 8 7

Gravel Pack

6

PMM

PMF 2040

PMF 1220

5 4 3 2 1 0

50

100

150

200

250

300

Average Sand Size (D50) in microns

Figure 70: Stratapac media selection chart

To accommodate these different sand characteristics, the screen media selection chart compares the average sand size (d50) with the distribution (d40/d90) and makes a screen selection based on the most appropriate sizing criteria. General Sand Control Information Manual External Revision 1.0 - 86

Comparison Tests In addition to our in-house testing, the concepts and design principles used in Stratapac & Stratacoil have been confirmed independently by a number of operators. Some of the results of such evaluations are presented below.

Fine Sands – 40/60 Comparison Test A major oil producer tested the relative plugging tendencies of various types of screen designs13. Included in the tests were 40/60 single screen consolidated pre-pack, 40/60 dual screen consolidated pre-pack, low profile 12/20 consolidated pre-pack, low profile 20/40 consolidated pre-pack, and the Stratapac Screen with PMM media. This technical report reviews the results of this paper with respect to the relative plugging tendencies of these screens. For these tests, the apparatus consisted of a 4.75" ID casing which contained a 2-7/8" nominal OD base-pipe screen sample. The screen sample contained a 4' length of actual screen material. A water-based slurry consisting of a 50/50 blend of SAE Coarse Test Dust and 70/140 mesh sand was made up to a 1500 ppm concentration. The slurry was pumped through the screen sample at 55 gpm. The test was run until the maximum differential pressure across the screen was 1500 psi. The results of the tests are shown in Figure 71 below. The Stratapac Screen reached the terminal differential pressure after being challenged with approximately twice the amount of contaminant as the 40/60 screens. The effluent from the Stratapac Screen visually appeared to be very clear, similar to the effluent from the 40/60 screens. 1600

40/60 Thin Pack

40/60 Pre-Pack

PMM 4060 Stratapac

Differential Pressure (psid)

1400

Effluent Particle Size Analysis

1200

12/20 20/40 PrePre-pack Pack

1000

Screen Type 40/60 Thin Pack 40/60 Pre-Pack 20/40 Pre-pack 12/20 Pre-pack PMM 40/60 Stratapac

800 600 400

1% Cut Point 356 355 89

200 0 0

0.5

1

1.5

2.0

2.5

Lbm Sand/Ft² Figure 71: Fine screens - plugging and retention

Interestingly, the Stratapac Screen, which has superior sand retention than the 40/60 prepacks, also took longer to reach terminal DP than either the 12/20 or 20/40 low profile screens. The tests for the latter screens were terminated around 900 psid because gravel was produced through both screens at that pressure. 13 S.A. Ali and H.L. Dearing, Petroleum International, July, 1996


In summary, the test results showed that the Stratapac Screen has excellent resistance to plugging. The screen has the retention rating characteristics of a 40/60 pre-pack screen, but the plugging characteristics of coarser screen materials. This is due to the higher pore volume achieved in the PMM material (52% vs. 32-36% reported for sand-packs made out of sieved gravel14) and the thin cross section of the PMM filtration material which has very little depth and therefore has a much reduced tendency to plug internally with solids. For a more detailed discussion on the effects of media porosity, please refer to Coarse Sands – 12/20 Comparison Test.

Medium Sands - 20/40 Comparison Test A major Gulf Coast operator performed a series of plugging/sand retention tests on a variety of screen media test disks. The tests included PMF2040 (sintered metal fibre), a sintered laminate wire mesh screen with a manufacturer’s rating of 125 microns, 25/35 Pre-Pack, 4 gauge wire-wrap screen (WWS), 6 gauge WWS and an 8 gauge WWS. The sand used in the tests was a synthetic mixture simulating a Gulf of Mexico sand with a D50 of 70 microns and D40/D90 ratio of 15 with 35% fines less than 44 microns in size. The plugging tendency was determined by measuring the pressure across the screen with respect to cumulative sand volume, and the removal efficiencies were measured during the course of the tests. Figure 72 & Figure 73 show some of the results of the tests. The removal efficiencies available are reported only for the first five minutes of the test to minimise the effect of cake formation on the apparent sand retention.

Plugging Potential 120

Delta P (Psi)

100 80 60 40 20 0 Cumulative Weight WWS (4 ga)

Pre-Pack 25/35

Mesh 125

PMF2040

WWS (6 ga) Figure 72: Plugging potential - 20/40

14 W.L. Pemberthy and C.M. Shaughnessy, “Sand Control”, Society of Petroleum Engineers, 1992


Removal Efficiencies

100 90

Removal (%)

80 70 60 50 40 30 20 0

20

40

60

80

100

120

Size (microns) Pre-Pack 25/35

PMF2040

Mesh (125)

WWS (8 ga)

Figure 73: Sand retention efficiencies

The results show that the PMF2040 media had a lower pressure drop than the sintered 125 micron mesh and better removal efficiency below 100 microns. The 25/35 Pre-Pack had better removal efficiencies below 100 microns than either of the metallic media but of course with much higher plugging tendency.

Coarse Sands – 12/20 Comparison Test A series of tests was performed by a major North Sea Operator to compare screen performance in terms of sand retention and plugging resistance. The originality of these tests was to address several issues that had been overlooked in other tests reported in the literature: •

Screen performance was evaluated simultaneously in terms of sand retention and plugging resistance

•

The sand tested was coarse and relatively poorly sorted while most published tests deal with either fine, poorly sorted sand (Gulf of Mexico type) or coarse and well sorted (Norwegian type)

•

The tests were a third party comparison of all new screen technologies recently introduced to the marketplace.

The data summarised below is more completely presented in SPE Paper 54745 (European Formation Damage Symposium, Den Haag 1999) and compares many screen types with equivalent ratings. Additional information provided by Weatherford Completion Systems is based on our understanding of the technology and the test results as presented to us by Norsk Hydro. The notes below can be inferred from the test data and competitor information as published in the public domain.


Code

Description

Sintered Fibre Mesh

Stratapac PMF 1220 and 2040 screens

Sintered Twill Mesh

Poroplus 250 media

Dutch Twill sintered)

Weave

(non- Baker Excluder 230

Pre-pack

Standard 12 gauge generic pre-pack screens (from Baker)

Wire-wrap

Standard 12 gauge generic wire-wrap screen (from Baker)

Wire-wrap 2

USF Johnson Superflo screen Table 24: Key to screen types

Test Method The tests consisted of challenging a screen test disc (approximately 95 mm) with water at a flow-rate of 5 l/min contaminated with a sand slurry suspended in a polymer solution injected at 10 ml/min into the water stream. Slurry viscosity and mixing conditions were such that the fluid reaching the screen had a viscosity close to water with a well dispersed solids suspension at a sand concentration of 200 mg/l with the flow going downward. Sand tested: d50 = 160 µm; d40 /d90 = 3.8 (see sieve analysis - Figure 74: Challenge sand sieve analysis).

% Weight Retained

100 80 60

d10 = 500 µm d50 = 160 µm d40/d90 = 3.8 d10/d95 = 11 5% fines

40 20 0 1000

100

10

Sand Size (µm)

Figure 74: Challenge sand sieve analysis

1. Produced sand was collected downstream of the screen in a sand trap throughout the test and its average particle size distribution was measured by Coulter Counter. 2. Sand retention was measured by weighing the sand that passes through the screen during the first minutes (first 20 litres) and corresponds to the sand retention of the actual screen before the sand filter cakes forms. 3. Based on the Media Selection Chart, PMF1220 medium was selected as most appropriate for this sand (Figure 75 below).


Uniformity Coefficient (d40/d90)

10.0 9.0 8.0

Gravel Pack Required

7.0 6.0

PMF 2040

PMM

5.0 4.0 3.0

PMF1220

2.0 1.0 0

50

100

150

200

250

300

Average Sand Size (d50), microns Brent Sand

Figure 75: Media selection chart with challenge sand plotted

Results •

Of all screens tested, the Stratapac screen exhibited the best resistance to plugging (Figure 76).

•

Stratapac PMF1220 screen retained sand very efficiently (Figure 77)

•

Stratapac PMF1220 controlled fines production (Figure 78).


7 1

2

3

5

4

6

5 4 1. Prepack 2. wire wrap 3. Wire wrap 2 4. Dutch twill 5. Sintered twill h 6. Sinteredfibre mesh

3 2 1 0 0

10

20

30

40

sand reaching screen (g)

Figure 76: Coarse sand screen plugging resistance test

Screen Retention Efficiency (%)

100

91

88

90 80

71

70

65

62

60

12 p ra

W

ire

-w

p ra -w

W

ire

ga

a) 2g 2

ill Tw ed

er nt Si

(1

M

ea W ill

Tw ch

ut D

es

ve

0 22 F1 PM c pa ta ra

h

50

St

pressure drop (bar)

6

Figure 77: Coarse sand - sand retention efficiency


50

30 Stratapac PMF1220 25

% Weight

Dutch Twill Weave 20 15

Sintered Twill Mesh

10

Wire-wrap 2

5

Wire-wrap

0 1000

100

10

Sand Size (µm) Figure 78: Coarse sand - effluent particle size distribution

Normally for screens with equivalent open area (connected porosity), a screen with bigger pores would resist plugging better as it would allow more sand to pass through. Referring to Figure 77, Excluder (88%) and Stratapac (91%) had roughly the same sand retention efficiency and by inspection of Figure 78 retained the same size particles. All things being equal, the screens should therefore have a very comparable plugging resistance. However, when looking at Figure 76, Stratapac has a markedly better plugging resistance. Referring to Figure 79, when Excluder and Stratapac screens are normalised to the same equivalent porosity, their plugging resistance curves closely overlay. This illustrates the significance of open area or porosity in filtration/screen design. In general, the more heterogeneous the sands the larger the performance difference is between PMF and the other screen types.

Screen Type Slotted liner Wire-wrap (90µm wire)

Approximate Open Area/Porosity 1.5% – 6% 6 – 25%

Pre-pack

35 – 45%*

Multi-layer wire-wrap (45µm wire)

11% – 40%

Metal mesh (Dutch twill weave, etc)

40% – 50%*

Sintered powder mesh – PMM Sintered fibre mesh – PMF

52%* 68% – 72%*

Table 25: Media porosity comparison


*NB: It is not practical to measure the open area of meshes or pre-packs as the actual open area would change with the depth and plane of the section and hence be open to interpretation/dispute. The asterisked values are hence (near absolute) porosity measurements and the effective porosity (connected pore space) could be expected to be marginally less. Certainly in the case of fibre mesh, it is not thought that this reduction is very significant as evidenced by Figure 79.

8 7 Pressure Drop (bar)

Sintered f ibre mesh 6

Dutch twill weav e

5 4 3 2 1 0 0

5

10

15

20

25

30

35

40

45

50

Weight of Sand/Porosity of Screen

Figure 79: PMF & DTW plugging resistance - normalised for porosity

Longer Service Life The tests detailed above confirm the principle that ‘filter’ porosity is key to service life. By delaying the onset of plugging and by providing a more permeable sand filter cake, PMF media will provide greater fluid throughput in the same time period or the same fluid throughput rate over an extended period of time. Due to the highly permeable nature of most modern screen designs, the well screen is not generally the rate limiting factor in a completion. Therefore, the main advantage to selecting PMF screen media is extended service life. All things being equal in terms of retention and flow-rates, the PMF screen could be expected to have a service life 50% to 100% longer than other screens performing the same job.


7. Gravel Pack Issues As Weatherford does not offer the complete range of gravel packing systems and services in-house, the procedures and processes are discussed in the main sand control training course. This section will point out some of the issues involved in the more complex gravel packing operations.

Horizontal Open-Hole Gravel Packing

Figure 80: Openhole gravel pack

In some situations, gravel packing can be simple and straight-forward. The gravel (with flush and push pills) into the screen/well bore annulus and the carrier fluid either leaks off into the formation or returns through the washpipe inside the screen. The gravel supports the borehole wall and provides a permeable medium through which the hydrocarbons can flow (Figure 80). Figure 81: Angle of repose (dry sand)

It is important to get a good pack. If the annulus is not completely packed and voids are evident, then the reservoir fluids will either travel up the unpacked annulus and not the screen, or will be funnelled through the void directly against the screen. The screen is often sized to retain the gravel and in such a situation, the formation sands will pass through at high rate often eroding the screen in short order. This phenomenon is called “hot-spot” erosion. The angle of repose of dry sand is 28° (see Figure 81). By inference, anytime the hole angle is greater than 62° (90° - 28°), the sand will have difficulty to propagate along the well bore. General Sand Control Information Manual External Revision 1.0 - 95

Figure 82 illustrates a horizontal well gravel pack with a partial pack resulting from higher than expected leak-off. The operation requires to be planned and executed very carefully. The gravel quantities and fluid volumes are calculated and pumped in controlled amounts. The mud cake on the well bore walls is scoured and reduced to a minimum by pumping at high rates (>300 fpm). The gravel carrier fluid is selected to be compatible with the drill-in and completion fluids to avoid emulsions. For most horizontal wells, the carrier fluid is water based and hence for best results, the drill-in fluid is a water based system. Again in horizontal situations with longer intervals, the pumping requirements are considerable as the gravel is pumped at high rate (>5 bpm). The gravel and carrier fluid exit the work string below the packer and form series of gravel dunes (the alpha waves). The design of the pack, fluid and pumping programme can vary the size of the dunes and the angle of repose to some extent. The variables in the programme are the amount of carrier fluid leaking off, the borehole stability and the borehole size. An excess of gravel is allowed for in the case of wash-outs. Carrier fluid can also bypass the annulus and flow through the wash-pipe/screen annulus. This also needs to be controlled (a wash pipe OD to Screen ID ratio of 0.8 is optimum). The screen OD should allow about 1” (0.75” minimum) radial clearance to formation for effective packing. Many long horizontals (>2000ft) are gravel packed, although there is much evidence of partial packs in these cases. Schlumberger have introduced the All-Pak system of shunt tubes to try to achieve a full pack. This requires a greater screen/well-bore annulus to allow for the tubes. Weatherford manufactures the Advance-Pack system for OSCA which achieves similar results with a smaller OD, and Halliburton also market the CAPS system.

Figure 82: Partial pack of long horizontal well

Gravel packing in horizontal wells therefore has the following issues that the operator should be aware of. •

Fluid compatibility issues with OBM drill in fluids. In certain situations, this may entail a complete (and expensive) swap out of drilling fluids between intermediate and final well sections

•

The risk of a partial pack is high, especially with high leak-off zones and poor well bore stability

•

The completion ID and hence production may be reduced (especially with shunt tubes)

•

Skin may be increased with sand/gravel mixing

•

Depending on rate, inflow profile and coning issues may be apparent

•

Safety (personnel & high pressure pumping) & logistics General Sand Control Information Manual External Revision 1.0 - 96

Cased Hole Gravel Packing

Figure 83: IGP cross-section

Cased hole gravel packs as shown in Figure 83 are cased and perforated wells which are then internally gravel packed. Flow from the reservoir sweeps into the well area and is then forced to flow radially and then hemi-spherically into the packed perforation tunnel. Flow through the tunnel is linear until it hits the gravel pack annulus where it may disperse until it passes into the screen. Once into the screen it is again concentrated over a base-pipe perforation and eventually enters the well-stream. Energy is lost in each flow regime. Each flow regime therefore has its own associated pressure drop. As the flow is concentrated into the perforation tunnel, the pressure drop associated with this flow regime is significant and also through the gravel pack into the screen. In a properly packed IGP, most of the gravel in the annulus will not see much production flow. The perforation tunnels require to be cleaned efficiently and packed completely without mixing with formation sands in an IGP. Figure 84 shows a typical perforation tunnel. The perforation tunnel should pass through the invaded zone (often called the mud filtrate or formation damaged zone) and into the virgin formation. The tunnel is lined with a small layer of highly compacted or fused rock from the high temperatures and pressures exerted by the General Sand Control Information Manual External Revision 1.0 - 97

explosive charge and the tunnel is filled with debris from the charge, casing, cement and rock. This debris needs to be removed and the tunnel cleaned. The tunnel should then be packed during the gravel packing process as long as the carrier fluid can leak off into the formation through the compacted zone.

Figure 84: Typical perforation tunnel

The choice of perforating gun is therefore important to •

Reach past the cement and damage zone to the virgin formation

•

Minimise the compaction zone

•

Minimise debris

•

Maximise the exposed production surface area

•

Maximise the exit hole diameter

If the formation is unconsolidated, the tunnel can be expected to collapse, in which case the exit hole diameter (ie the hole size through the casing) can be maximised at the expense of depth of penetration through the use of big-hole charges, as the tunnel will need to be prepacked.

Figure 85: Perforation packing General Sand Control Information Manual External Revision 1.0 - 98

The tunnel should be pre-packed (Figure 85) to achieve maximum permeability. Studies show that if the gravel and formation sands get mixed in the tunnel, permeability and hence production is severely impaired. Hole deviation, perforation orientation and poor leak-off into the formation also severely affect tunnel packing efficiency.

Figure 86: Effective of formation damage

Gun centralisation, perforation charge performance and formation damage can also significantly affect productivity as shown in Figure 86. A study of the various gravel packing techniques is presented in Table 26. This illustrates the increase in skin that can be expected even over EGP techniques. Interestingly, chemical consolidation gave good results, but this is effective over relatively short intervals (typically 10ft with epoxy resins). The IGP completions however allowed the client to produce at a higher sand free rate than without packing and so were considered successful. Gravel Pack Productivity Comparison (same field & similar lengths) Method

Skin

Flow Efficiency

IGP

25

22%

EGP

11

38%

Under-Reamed GP

6

53%

Sand Consolidation (short lengths)

2

75%

Table 26: GP productivity comparisons

Gravel Sizing and Screen Selection The next issue is to select the most appropriate gravel. Incorrect sizing of gravel and screen can cause many problems with well productivity and premature completion failures.

Sieve Analysis Data The proper sampling of the formation sand is critical in determining the gravel size. The essence of sieve analysis is to obtain the correct formation grain size and size distribution. General Sand Control Information Manual External Revision 1.0 - 99

Therefore, correct procedure and interpretation of the sieve analysis results are crucial to the selection of the appropriate gravel size. The following gravel sizing is based on three field samples and are assumed to be representative of the formation sand (see Figure 87).

100 90 80 60

Depth 6460'

50

Depth 6270'

40

Cum Wt %

70 Depth 6370'

30 20 10 0 1000

100

10

1

Sieve Size (mm)

Figure 87: Example formation sieve data

Gravel Size Selection Gravel pack sand must meet the requirement of API RP58 recommendation (sorting, sphericity, roundness). The correct choice of gravel size will ensure the following: •

Preventing formation sand intrusion into the gravel pack

•

Minimising the permeability impairment within the gravel pack

•

Providing maximum productivity by minimising the skin.

Proposed Gravel Sizing Criteria There are many gravel sizing formulae published to date which are defined based on a diameter ratio of gravel/sand at certain percentile. At present, the most popular criterion is the Saucier’s formula that is the diameter of gravel should fall within a range of 5~6 times the diameter of formation sand at 50 percentile (d50). The Saucier’s formula is fine for uniform sand. The dg/df ratio and the uniformity coefficient (Cu=d40/d90) are the key parameters to design the gravel size and screen size. Ren proposes the design criteria should be adjusted for poorly sorted sand (Cu > 5), and d75 should be used instead of d50 to design the gravel size.

Limitations of the existing gravel sizing formulae For example, the Saucier formula is used to illustrate the shortcomings of the existing formulae for gravel size selection. Sand A and sand B have the same 50 percentile diameter (105 microns). However, the sorting is different. According to Saucier’s rule, mesh 20/40 gravel will be selected for both the sand A and sand B (see Figure 88).


Sand A Sand B

1000

100

10

Cum Weight (%)

100 90 80 70 60 50 40 30 20 10 0 1

Sieve Size (micron)

Figure 88: Limitations of Saucier's rule to gravel sizing

It is obvious that the existing formulae are too general to meet the requirements of various formation sand controls. Post placement evaluation also shows that there are certain limitations of the existing gravel sizing formulae. This is mainly due to the lack of consideration of the geometry of the pack structure, the impairment mechanism, and the sorting of both gravel and formation sand.

Pack Structure Arrangements Successful gravel packs require good gravel size selection. In order to have a better understanding of the fundamental properties of the gravel pack, it is important to investigate the actual packing structure arrangements. Ren has developed a modelling technique that can simulate 3D gravel pack structure (see Figure 89), which assists in understanding the effects of the pack structure arrangement and its properties. The model-predicted results agree well with the experimental data.

Figure 89: 3D Gravel pack structure generated by 3D modelling


Pore Throat Distribution The gravel pack structure determines its porosity, permeability and pore throat distribution. For a given sand size distribution, the pore throat distribution dictates the bridging/plugging ability of the gravel pack. The size of the formation sand, which can invade the gravel pack, will depend upon the pore space/throat of the gravel pack structure (see Figure 90).

100 90

70

2040 GP 3050 GP

60

4060 GP

50

5070 GP 40

1220 GP 30

Cum Percentage (%)

80

1630 GP

20 10 0 1000

100

10

Sieve Size (microns)

Figure 90: Gravel pack Pore Throat Distribution (PTD)

New Gravel Size Criteria Based upon the pore throat distribution (PTD) of the pack structure, the candidate gravel is selected based upon the closest curve match of the formation sand size distribution and the pore throat distribution of the gravel pack. This new criteria, which considers both gravel and formation sand distribution, guarantees that the formation sand forms an interface/external cake on the candidate gravel. Hence mesh 40/60 and 50/70 gravel should be the candidate gravel sizes for the example field sand control by using the new criteria. Mesh 40/60 gravel size was eventually used successfully due to availability issues.

100

1630 GP

80

2040 GP

70

3050 GP 4060 GP

60 50

5070 GP

40

1220 GP

30

Depth 6460' Depth 6270'

20

Depth 6370'

Cum Percentage (%)

90

10 0

1000

100

10

1

Sie ve Size (m icrons )

Figure 91: Curve match of the gravel pack PTD with formation sand PSD General Sand Control Information Manual External Revision 1.0 - 102

Sand Invasion Mechanism Proper prediction of gravel pack permeability impairment requires good understanding of the sand invasion mechanism. The sand invasion mechanism has a strong relationship with the final permeability of the gravel pack, the well life and well performance (PI). The ideal invasion mechanism is interfacing bridging, which will form an external filter cake and prevent the formation sand from invading the gravel pack deeply (see Figure 92). Gravel Pack Sand

Formation Sand

Screen

Figure 92: Schematic of interfacing bridging

The bridging effects can be modelled by computer. For example, the above arrangement was checked by generating the 3D packing structure of the 40/60 mesh gravel. Then, individual grains of the formation sand (based on the formation sieve analysis) were randomly selected by the model and tracked as they flowed into the gravel pack sand. The formation sand grains either bridged at the surface of the gravel pack, invaded and bridged within the pore throat structure of the gravel pack, or flowed completely through the gravel pack. The model kept track of all the particles and calculated the permeability of the gravel pack sand as it was invaded. The model was run until the permeability through the gravel pack stabilised. Based upon the simulation, it can be seen clearly that mesh 40/60 gravel can form an interfacing bridging, which will form an external filter cake and prevent the formation sand from invading the gravel pack (see Figure 93).

Figure 93: Bridging mechanism with example data

In conclusion, 40/60 gravel was selected over 20/40 and this choice was confirmed experimentally and in the field. The wells had previously been completed with 20/40 systems and performed at high rates initially until the fines invaded the pack. Although 40/60 has General Sand Control Information Manual External Revision 1.0 - 103

initially less permeability than 20/40, the total system permeability after sand filter cake stabilisation was superior. Two important conclusions can be drawn from this exercise: •

Interface bridging is achieved by more closely matching the gravel pore throats with the particle size distribution. Note this is a non-uniform approach and has parallels with Stratapac media selection

•

Using standard gravel pack sizing systems based on the Saucier criteria (or derivative thereof) may give non-optimal well performance in non-uniform sands.

•

Modelling can lead to non-intuitive results which need to be supported by lab testing. Testing should be as holistic and realistic as possible.


8. Expandable Sand Screens Introduction Figure 94 illustrates the differences between EGP and ESS in the case of a 20 API oil reservoir drilled with a 6” open-hole. ESS when installed would have an ID of at least 5” and up to 5.5”. For a GP, the options are to use a 3.5” screen (or a 2.7/8” screen if using shunt tubes). The tubing intake curve (VLP - Vertical Lift Performance) is assumed to be the same for all completion types. The Inflow Performance (IPR) curves for the various ESS/EGP completions indicate the ability of the reservoir to produce through the sand-face completions. A “solution point” is where the VLP and IPR curves intersect and this indicates steady natural flow. The solution points vary by over 4,000 bpd between ESS and the 2.7/8” EGP completion.

Figure 94: Productivity comparison for a various ESS & EGP completion options in a 6" heavy oil producer

Figure 95 compares the flow contribution of five equal intervals along the length of the well. The ESS completion clearly has a more even inflow, which of course has several advantages in terms of reservoir management: •

Production rates considerably more than equivalent gravel pack rates

•

Reduced and more even draw-down for production along the wellbore length (less prone to sanding and better mud-cake lift off).

•

Even production inflow giving more efficient reservoir drainage

•

Reduced risk of early water & gas breakthrough

•

Well slimming General Sand Control Information Manual External Revision 1.0 - 105

Figure 95: Flow contribution along well bore of various ESS & EGP completions

These benefits are derived purely from the increased ID available for production. The productivity gains of using ESS in a 6” hole are roughly equivalent to that of a standard EGP in a 8.5” hole, hence the use of ESS allows the operator to slim down his well. This concept is referred to as “well slimming” and is causing much operator interest in this product. Additionally, there are two further benefits to an ESS deployment. Firstly, the more even draw-down along the well should improve the consistency of mud cake removal along the well bore length. Secondly, there will be some skin improvements in the near well bore area as less fluids will have been pumped with ESS than in an EGP. In horizontal wells, this benefit is less apparent however. The reduction and elimination of the annulus gives the following benefits: •

Formation sands/clays/fines do not mix in the annulus and plug completion

•

Zonal isolation & control is possible

•

Increased number of remedial options

•

Remedial options still provide a sufficient ID for high rate production

•

Production logging data is useful.


ESS Construction The ESS is made of metallic components designed to withstand the toughest well environments. It combines four basic elements to deliver sand control in various well conditions while maintaining high reliability, longevity and optimum hydrocarbon production. Its basic components are: •

Base pipe

•

Filtration media (Petroweave)

•

Outer protection shroud

•

Integral expandable connector

Expandable Base-Pipe Filtration Media (Petroweave)

Petroweave attached to base-pipe Expandable Protective Shroud Figure 96: ESS Construction


Top connector houses the expansion cone.

ESS Joints are normally supplied in 11.6m lengths and are 11.5m when made-up (4.71” make up loss)

Shoe assembly with cone catcher After expansion the cone is left secured in the cone catcher at the base of the ESS assembly.

Figure 97: ESS Assembly


Base Pipe and connections The ESS base pipe is a robust Expandable Slotted Tube (EST) capable of expanding up to 80% in diameter, depending on the size of base pipe selected. The base EST provides a very large inflow area for the produced fluids. The base pipe has the ability to go through short curvature radius making it an ideal choice for deployment in horizontal holes. Because the pipe is slotted, the ESS becomes more tolerant to larger bending moments, displaying class leading flexibility (ie 5-1/2” ESS can be deployed through 30°/30m doglegs; it will fail only at 43°/30m dog legs). The ESS joints have integral expandable connectors with no blank areas to obstruct flow. Each joint has both a pin and a box connection, which are designed to provide a mechanical interlock (for strength) during deployment and expansion. The Petroweave filter on the connectors overlap after screwing together the ESS joints, providing a sand tight connection. The connector is a critical element of the ESS system and has been extensively tested to prove sand exclusion capability after expansion. The flush connectors are made of Super Duplex Stainless steel to provide high tensile and bending strength (ie tensile yield of the 5-1/2” ESS is 230,000lbf). Figure 98: Stabbing in ESS pin connection

Figure 99: ESS Connections

Filter Medium (Petroweave) The filter medium Petroweave is a metal weave designed to provide maximum filtration/flow area, thus maximising resistance to plugging effects. The Petroweave is manufactured in both 316L and Nickel Alloy (Incoloy 825) offering compatibility with most corrosive well environments. Following extensive testing to select the filter medium, Petroweave filters with nominal sizes ranging from 150 micron to 270 micron were chosen as elements of the ESS to suit different sandstone types and operational preferences. General Sand Control Information Manual External Revision 1.0 - 109

The Petroweave is attached to the base-pipe using a process that ensures the integrity and uniformity of the sand exclusion apertures. The filters overlap each other along the length of the base pipe and accommodate the circumference increase during expansion while remaining sand tight. Correct selection of the Petroweave filter should aim to restrain the load bearing grains of the formation sand from passing into the well-bore. These grains will naturally bridge the formation sand against the ESS, controlling sand influx in the process. Figure 100: Expanded ESS

The sand control capability of the Petroweave is enhanced because the screens are placed in direct contact with the well-bore, reducing movement of formation sands in the annulus. As a result, the well-bore remains stable throughout the life of the well and risk of hole collapse is decreased. Furthermore, with restricted fines migration, near well-bore impairment is reduced. In cased hole applications, the ESS will outperform traditional screens by eliminating annular fill.

Outer Protection Shroud The outer protective shroud ensures the filter medium is not damaged when running the screens in hole. It also acts as the encapsulating layer, ensuring the filter media remain tightly sandwiched together following the completion of ESS expansion.

Expandable Isolation Sleeve (For Information) The Expandable Isolation Sleeve (EIS) is a complimentary product to the ESS designed for use in wells where zonal isolation may be required during the well life. Current practices for open hole zonal isolation involve the use of External Casing Packers, which have proven with time to be unreliable due to cement shrinkage and complex installation procedures. The EIS is constructed in a similar manner to ESS enabling it to be made up in the ESS string in the same manner as the ESS at the correct space out. EIS uses a HNBR rubber coating on the protective shroud, which is energised against the formation during the expansion process preventing annular flow. Should it be necessary later in the field life the EIS may be reenergised against the formation using inflatable packer set inside the EIS.

Expansion Systems Solid Cone The solid cone (shown below) is pre-installed in the ESS ETC (Expandable Top Connector), fitted with the standard 7.375” OD tungsten carbide cone ring (to suit 8.500” hole). The solid cone is easily removable from the ETC if so desired. The body is a two part assembly, which holds the cone ring. The cone holder is supplied with a suite of cone rings, to suit irregular hole sizes. On the outer surface of the cone body are four slip segments. These locate in profiles in the EBC (expandable bottom connector) to ensure the cone remains at the bottom of the ESS. Tests have shown that this feature is NOT necessary, but is included as an additional safety feature. Figure 101: Expansion Cone

To date, the majority of ESS field expansions have been performed using this method. A second expansion method General Sand Control Information Manual External Revision 1.0 - 110

integrates the cone with the expansion mandrel so that the cone is retrieved. Whatever method is utilised it is essential that the borehole geometry is maintained within the surplus expansion limits of the ESS in order to achieve both full expansion and borehole support.

Expansion Mandrel The expansion mandrel shown below is deployed on the end of the expansion string on all solid cone, two trip systems. The mandrel passes through the cone body, centralises in the unexpanded ESS and engages with the inner shoulder in the cone body. Figure 102: Expansion mandrel

Rotary Expansion A range of Rotary Expansion tools is in development, which can be deployed on drill pipe or coil tubing. Driven by a PDM mud motor, they improve the deployment options and expansion performance of the expandable product line. The rotary expansion tool is available as a selective device which will pass through restrictions (eg packer bores). Following deployment and expansion the tool can be functioned to “collapsed mode” allowing retrieval. Experience suggests that the use of rollers for expansion reduces the required expansion forces by 66 – 75 % by eliminating friction, thus extending the length of ESS that can be expanded in extended reach wells. Additionally, this system can be retrieved and reset to a smaller open OD should a restriction in the well be encountered.

Figure 103: First 4” Compliant Rotary Expansion System (CRES) tool as used on Shell Brigantine

Figure 104: Non Compliant Rotary Expansion Subassembly General Sand Control Information Manual External Revision 1.0 - 111

Figure 105: Compliant Rotary Expansion System

The CRES tools consist of roller cones in the nose which expand the EST to a fixed size. The balls in the compliant section above then move out under hydraulic pressure and force the EST outwards still further to ensure it conforms to the bore-hole wall. This system is still under intensive development and its first application occurred in October 2000 when it was used to expand 4000ft of 4” ESS in a North Sea well. This first use of the system actually used two trips, the first trip used a “conventional” fixed cone system to expand the ESS out initially as a precaution. The second trip was with the CRES device which expanded the screen out to conform to the well-bore. The intention is of course for rotary expansion in one trip (two trip deployment) and this should be achievable by year end 2001. Longer term, the intention is to deploy ESS and expand in one trip (single trip deployment/expansion).

ESS Mechanical Properties TESTED MECHANICAL FIGURES The following figures are the results of testing to destruction under laboratory conditions. These figures are for information only and on no account should be quoted for operational issues. A safety factor should be adopted at all times, and as such, the rule of thumb for operations is to divide these figures by 2.

2 7/8"

3.5"

4"

4.5"

5.5"

Tensile Yield (lbf)

100,000

100,000

125,000

175,000

Tensile failure (lbf)

134,000

140,000

188,000

230,000

Compressive Failure (lbf)

63,000

66,000

107,000

122,000

53

43

42

43

2,240

2240

2240

3,500

3,500

3500

20,000

25,000

35,000

Bend (°/100ft) Point load collapse resistance (psi) Rotational Torque (Ftlbf) Expansion Force (lbf)

30,000

20,000

Table 27: ESS application limits


ESS Wall Pipe OD Size (in) Thick

Pipe ID

Wt/Ft

Box OD Box ID

Filter Width

Max Final OD

2.875

73.03 2.875

7.01 0.28

59.01 2.32

2.67 5.89

83.8 3.30

59 2.32

200 7.87

114.42 4.50

3.5

88.9 3.500

5.49 0.22

77.92 3.07

3.49 7.70

99 3.90

74.5 2.93

120 4.71

133.35 5.25

4

101.6 4

5.74 0.23

90.12 3.55

4.2 9.26

112.4 4.43

87.3 3.44

140 5.49

158.75 6.25

4.5

114.3 4.5

6.02 0.24

102.26 4.03

4.97 10.96

124.5 4.90

100 3.94

160 6.28

184.15 7.25

5.5

141.3 5.56

6.55 0.26

128.2 5.05

6.74 14.86

151.5 5.96

127 5.00

200 7.87

232.41 9.15

Table 28: ESS dimensional data (mm & inches)

ESS Installation Procedures The ESS system can be installed using either a one-trip or a two-trip system. Note that the one trip system requires further development to allow this to be applied over all ESS sizes and systems. The two-trip system is currently used as standard. In the two-trip system, the ESS is conveyed in the same manner as conventional non-gravel packed screen, ie below a liner hanger or packer. The ESS and liner hanger can be run with a concentric wash string which allows circulation through the ESS via a wash down shoe string. The wash-string makes the running string stiffer and this factor should be considered in Torque & Drag (T&D) modelling. The use of the wash-string, although a complication, may be required for well control and mud conditioning considerations and this is a drilling & client decision.

Torque and Drag Before any ESS installation, it is necessary to run a Torque & Drag simulation to ensure: •

The ESS can be safely deployed to TD without exceeding its mechanical limits or inducing helical buckling into the string

•

The ESS can be safely expanded in its entirety without the expansion string exceeding its mechanical limits or inducing helical buckling into the string.

•

Hydraulic factors do not limit the activation of key system components, eg liner hangers or expansion cones.

Weatherford Completion Systems make extensive use of the Landmark Torque and Drag software package to determine whether a particular ESS can be safely deployed in the well. The interval length is not limited by hydraulics as is the case with gravel packing. Rather the limit to the length of ESS that can be expanded using conventional “weight on bit” from the General Sand Control Information Manual External Revision 1.0 - 113

drill-string (or with mud pump hydraulic power) is limited or dependent on a number of factors: •

The trajectory of the entire well to surface

•

The availability of required drill-collars, drill-pipe, etc

•

Prevailing hole sizes and friction factors, often dependent on mud types, formation types, casing grades

•

The type of expansion mechanism used.

The use of the CRES tools is expected to extend the envelope of possible candidate wells. Physical testing representative of field conditions is difficult to simulate in test wells as they do not contain long reach sections where achieving WOB is difficult. To date, the validation and fine-tuning of the T&D model has been achieved via observation of expansion performed in real applications. Most wells and certainly all highly deviated or horizontal applications would be modelled when full well data was made available to ensure the appropriate weight on bit (no of drill collars) can be achieved.

ESS Expansion Forces ESS Expansion is achieved by slacking off weight from the expansion string to lay down weight on the expansion cone. For 5.5” ESS, the following forces can be expected. •

Unlubricated expansion forces, as expected in testing, can range from 35k – 50k Lbf

•

Lubricated expansion forces, as expected down hole, can range from 35k – 40k Lbf.

The above information is relevant to a one or two trip system with a solid Tungsten Carbide expansion cone. Tests conducted with the 3.5” roller cone show expansion forces of 4000 lbf, compared with the 12,000 – 16,000 lbf expansion force using a solid cone.

First Trip Having made up all the T&D pre-determined ESS joints with blank pipe and packer/hanger, the entire system is run to depth on a drill pipe work string. When on depth, the packer is set within the liner, using conventional procedures; ie drop ball, pressure up to set, anchor test and pressure test. The running tools would then be released, and the work string retrieved to surface.

Second Trip (Conventional Cone System) The expansion string would consist of the Expansion Mandrel and appropriate drill collars and heavy weight drill pipe determined by T&D simulation. Once the Expansion Mandrel is landed on the Expansion Cone located on the top of the ESS, slacking-off weight shears out the locking screws of the Expansion Cone, and the expansion would be initiated. Expansion would continue until the cone lands at the bottom of the ESS. The expansion string would then be pulled and retrieved back to surface.


Typical running time for 150 m of ESS (13 joints) set at 2,500m With the Two-Trip System OPERATIONS 1. 2. 3. 4. 5. 6. 7. 8.

Make-up-up bottom screen joint c/w cone catcher profile and bull plug Make up ESS joints Make-up top joint of ESS complete with pre-installed expansion cone Make-up crossover to blank pipe Make-up blank pipe space out pipe as required Run inner string/space out Pick up Packer (or liner hanger) Make up inner and outer string connections

9. Run entire System to depth on Drill Pipe 10. Drop ball/Carry out setting sequence for Packer 11. Close the pipe rams and pressure test the annulus to ensure packer seal integrity 12. Confirm anchor/test and pressure/test, release running tools

TIME 3 hrs.

2 hrs.

8 hrs. 1 hr.

13. POOH with Running tool

5 hrs.

14. Make up expansion string with enough drill collars/drill pipe to provide 35,000 lbs. Net down-hole force and RIH 15. Latch into expansion cone / shear pins 16. Initiate expansion 17. Expand ESS joints 18. Land out expansion cone to bottom ESS joint 19. POOH with expansion string 20. END

7 hrs.

Total time Table 29: Operation time estimate


1 hr.

8 hrs.

35 hours

ESS Deployment (Two Trip System)

1) Make-up screens 2) Make-up Packer setting tool 3) Run in the hole 4) Correlate depth 5) Set packer and test 6) Release running tools Figure 106: Two trip installation: Trip 1 - Set Hanger


8)

Make up Expansion string

9)

Run in the hole

10)

Engage expansion cone

11)

Expand ESS

12)

Pull out of the hole

Figure 107: Two trip installation: Trip 1 - Expand screen


Pre-Installation, Well Prep, Clean-Up & Logging In order to drill and maintain an optimum hole through the reservoir, it is important that all the relevant personnel have an early involvement in planning the operation and developing the programme. The relevant people should perform hazard identification and develop contingency plans, select the most appropriate fluid, determine the data acquisition requirement, etc, etc. Hazard identification and mitigation needs to be carried out on the processes required to install an ESS, highlighting the critical issues affecting the installation such as: •

The quality of the reservoir section; require a gauge hole, a clean hole (cuttings free).

•

Fluids strategy from drilling to well clean-up.

Proper selection and design of the drilling fluid has a major impact in the success of the operation. The mud type selected must be optimised to achieve the following: •

Aid the drilling of a close to gauge hole, including the prevention of interstitial clay expansion to enable the maximum cone size selection in order to achieve borehole support

•

Controlled maximum particle size during the drilling of the reservoir section requiring the use of sized barite or bentonite. Solids control activities should include the use of the finest mesh screens practical to maintain a particle size less than 1/3rd and preferably 1/6th the size of the ESS mesh. The centrifuges typically should be run in barite recovery mode continuously while drilling the reservoir section. It is recommended that while drilling the reservoir section, particle size tests are made at regular intervals to ensure the maximum size is maintained below the pre-determined maximum. Test disks can be provided to allow this to be checked and monitored at the well site.

•

To achieve little to no residual cuttings or debris and a thin and tight wall cake, the mud should be treated to provide minimum fluid loss (good mud filter cake), optimum rheology for hole cleaning, optimum solids content and quality.

If any well-bore areas logged indicate potential problem zones, a check trip to TD is recommended to ensure there is a clean hole with no suspected hole problems. A heavy weight pill may be pumped around to ensure the hole is clean. Additionally, consideration should be given to provide on-site hole cleaning tuition to the offshore personnel.

Data Acquisition For ESS Deployment The data acquisition should aim to deliver a good well and to identify potential problems that may arise during the sand face completion. The information should help to assess how the well is being drilled in relation to the plan. It is recommended that caliper information be obtained prior to a gravel pack or an ESS installation. The caliper information allows the well-site personnel to select the correct fixed cone prior to running the completion. With the use of the compliant rotary tools and experience in a particular field, the importance of this information will be reduced. Note that for gravel packing, an estimate of borehole volume is also of importance to check that the required quantity of gravel has been used and that the pack is complete. •

Mud Logging - helps to identify any possible fluid problems that could affect the deployment and expansion of ESS.


•

Navigation tools such as Rotary Steerable Systems coupled with GR/Resistivity and Near Bit inclination sensors (ie Autotrack) result in better hole quality since the constant rotation improves hole cleaning. Furthermore, it avoids the micro-doglegs caused by rotating and sliding directional motor systems.

•

Modular Drilling Dynamics and Pressure - this information could be used to optimise drilling and to avoid excessive vibration, possible tool failure and over-gauge holes. It also assists in identifying possible problems removing cuttings from the well-bore.

•

Electric Line Logging - Caliper data used for the selection of cone size can be obtained during open hole logging. A high mud weight may preclude the use of ultrasonic imaging tools, but in general these are easier to obtain in horizontal wells. An independent six arm caliper tool, such as can be provided on dipmeters, provides a good indication of borehole shape. Borehole image logs (eg FMS, STAR, CBIL, UBI) have been proven in previous applications to have adequate accuracy to determine hole size/shape and rugosity prior to expansion.

Use of ESS in Combination with Other EST Products ESS was designed to be run in combination with other Weatherford expandable products to provide sand face completions that meet different reservoir management needs. It can be run in combination with Expandable Completion Liner (ECL), Expandable Isolation Sleeve (EIS), Rubber Coated ECL-R, and blank pipe. For instance, blank pipe would be deployed across the unstable cap rock to prevent collapse while ECL would provide hole support in the formation below the cap rock. Rubber coated ECL could provide an annular seal after expansion to make selective treatments across different zones possible using inflates or packers. Finally, ESS would be deployed to control sand in zones with weak compressive strength.

Accessory Equipment The ESS system can be run with standard completion equipment such as circulating shoes, blank pipe, seal-bores, fluid loss control devices, packers and liner hangers. Weatherford can supply the entire system requirements. It is recommended that a packer or liner hanger with the largest bore be selected to run with the ESS system to avoid restrictions that could choke production or limit the capability for future intervention work. Weatherford has designed and can provide a range of EXP packers to fulfil this requirement and has available a wide range of suitable liner hangers.

Technical Issues Minimum rat-hole requirements There is normally a requirement to have the ESS expanded over the entire sandface length and sometimes, due to the active aquifers for example, the rat-hole must be minimised To minimise the rat-hole would require the length and number of components beneath the ESS to be limited. The most effective way to do this is to run the ESS without a concentric inner string for circulation. If the benefits of an inner string are minimal, this string should be eliminated if possible. Without an inner string there is a requirement only to run a x-over with bullnose on the bottom of the ESS system in order to make the system sand tight. This would result in an approximate length below the fully expanded ESS section of 2 – 3 ft. The issue of expanding the ESS from a semi-submersible rig whilst ensuring that maximum sit down forces are not exceeded on the ESS can be addressed over short sections by General Sand Control Information Manual External Revision 1.0 - 119

introducing a no-go to the expansion string which lands on top of the packer or liner hanger. This will physically prevent the expansion tool from travelling further than required, although extreme caution would still be required not to exceed the maximum set down weight on the liner hanger or packer.

Mud filter cake removal One of the primary requirements for the drill-in fluid, alongside hole cleaning properties and well control properties, is to produce a thin cake, which minimises leak-off and hence formation damage. Normally, during the well clean up, this filter cake is back-produced through the ESS. A series of tests carried out by an operator on producing filter cake back through the ESS has provided a useful insight into the filter cake behaviour as ESS shroud and mesh is pressed into the cake and a draw-down applied. The test set used a ceramic disc with a 5mm filter cake, a layer of expanded perforated plate as used for the outer shroud of the ESS and a layer of ESS weave, all pressed together. Oil was then flowed through the ceramic disc and through the ESS. Although it is not possible to release the results of the test, the picture below shows the test piece at conclusion of the testing. In clockwise order from top left the pieces are, ceramic disc, perforated plate, lower screen, upper screen. It can be seen from the pictures that an absence of filter cake is noted on the weave over the area that the perforated plate sat and that the filter cake is still in place in the perforated plate.

Figure 108: Photographs following mud filter cake removal testing General Sand Control Information Manual External Revision 1.0 - 120

It has been concluded as a result of this testing, that during phase from ESS expansion to filter cake production the following occurs: •

The ESS is expanded to contact the borehole with a radial force of 2,000 lbf. As this happens the filter cake adjacent to the gaps in the perforated plate is pressed into the depth of the outer shroud down to the mesh

•

The filter cake adjacent to the solid area of the perforated plate is pressed firmly into the formation

•

Following the running of the upper completion, the well is drawn down to below the pre-determined mud cake pop off differential and the well is cleaned up. From the pictures, it can be seen that the mud cake trapped against the weave begins to be produced (lower left and right). But where the filter cake has been squeezed between the expanded shroud and the ceramic disc / formation, the filter cake remains in place though considerably less thick.

•

Consequently, there is no loss of borehole support in the ESS system occurs as a results of the filter cake removal.

ESS Media Testing The following tests have been performed on both the individual elements and the complete ESS system to verify sand exclusion capability and mechanical properties to resist various well environments.

Filter media plugging tests Different filter media types were tested to identify a media with the best sand control characteristics whilst maintaining high resistance to plugging. S O U T H E R N N O R T H S E A P E R M IA N S A N D S T O N E (P .I. = 3 6 0 B B L /D /F T ) 3 5 3 0 2 5

(PSI)

SCREEN PRESSURE DROP

4 0

2 0 1 5 1 0 5 0 0

1 0

F L O W IN G

2 0

T IM E

(M IN S )

2 0 0 M IC R O N S IN T E R E D W E A V E 2 0 /4 0 P R E - P A C K E D S C R E E N S 2 0 / 4 0 S IN T E R E D M E T A L S C R E E N S 2 0 0 M IC R O N E S S

M EM B A N E

Figure 109: Comparative screen plugging tests


Filter media erosion tests Erosion tests were performed using sand particles accelerated with compressed air through a gun nozzle. Based on the results of the tests, it was concluded that a specific weave had the best erosion resistance over similar ‘family’ filters and this was selected as the base design for Petroweave meshes. The photographs shown below depict the results of destructive testing.

Hollander Plain Weave

Petroweave

Figure 110: Erosion testing

ESS sand exclusion/integrity tests These tests were performed on both pre and post expanded ESS to document its capability to exclude sand grains with particle size equalling the nominal apertures of the screen. All the tests showed absolute sand retention, confirming the sand tight effectiveness of the ESS connector and weave overlap design.

Figure 111: Sand exclusion testing

ESS mechanical tests This set of tests was aimed to identifying the mechanical strength of the ESS under compression, tension, bending, crush, and collapse loads. This information is used to optimise the planning and execution of jobs.

Figure 112: ESS connector strength testing General Sand Control Information Manual External Revision 1.0 - 122

Figure 113: ESS mechanical testing

ESS expansion tests Numerous expansion tests have been performed for various ESS sizes whilst simulating a wide range of expansion conditions in the expansion test bay and at a test drill rig in Aberdeen.

Borehole Support Borehole support was discussed in Section 3. The derivation of the computer model used to determine ESS suitability in a highly deviated or horizontal well is discussed later in this section.

Surplus Expansion One of the key features of ESS is that it eliminates the annulus, even when the borehole is not ‘’gun barrel gauge”. This property is known as ‘surplus expansion’. The configuration of the slot pattern causes the pipe to flow over the expansion cone when driven though it, giving a larger ESS bore than the cone OD plus screen thickness. The amount of surplus expansion is related directly to the expansion cone lead angle and whether the expansion edge is sharp or graded. Much research has been conducted on ascertaining the most effective cone design. Reducing the cone angle decreases the expansion force and the surplus expansion; increasing the cone angle increases the expansion force and the amount of surplus expansion. All fixed cone configurations have been standardised to give appropriate surplus expansion without excessive expansion forces. Based on theoretical models, test results and field experience, the amount of surplus expansion for the 5.500” ESS expanded with a standard cone will be a minimum of 4%. The following is an example calculation for 5.500” ESS in 8.500” open hole: Cone OD plus 5% Surplus ESS Thickness

7.375 inches 0.300 inches (4% of cone OD) 1.000 inch (0.5” per side)

Table 30: Surplus expansion (i)

Therefore, expanding a 5.500” ESS using a 7.375” cone, the minimum theoretical ESS OD will be as follows: (Cone OD) 7.375”

+ (ESS thickness) + 1.000”

+ (Surplus Expansion) + 0.300”

= Expanded ESS OD = 8.675”

Table 31: Surplus expansion (ii) General Sand Control Information Manual External Revision 1.0 - 123

Therefore open hole size can vary between 8.375” minimum to 8.675” maximum to guarantee full bore hole support and full system expansion.

C =ESS Thickness = 1.00in

A = Surplus Expansion = 4% B = Cone OD = 7.375in

A B

A + B + C = Expansion OD

Figure 114: Surplus expansion


As the surplus expansion can vary, usually the worst case is used for prediction purposes. However, in a measured sample piece surplus expansion was found to average 5.3% over the joint and 4.1% at the connector. Note that for general purposes, surplus expansion is quoted as being 4%. amount of minimum expansion, which could be achieved at the connector.

This is the

The use of the rotary compliant tool may change this value slightly. The initial roller nose section will result in surplus expansion similar to the fixed cone. The compliant section should expand the screen still further.

Benefits of Borehole Support The interaction between the Expandable Slotted Tubulars (EST) and formation rock has been studied. Note that this data is not limited to ESS sand screens. Specifically, experimental tests were carried out and analytical solutions in combination with empirical methods were used to study the EST rock interaction. A preliminary quantification of the borehole stabilisation effect of the EST when it is applied directly against the open hole has been derived. The results obtained so far have shown that the stabilisation effect of EST is significant. Experimental thick-walled cylinder tests with EST support suggests that the EST can increase load bearing capacity of the borehole by approximately 70%. An analysis of typical field data shows that the use of EST would improve significantly the hole stability of horizontal open-hole completions. The typical field input parameters required are the in-situ stress (effective overburden stress) and thick-walled cylinder strength.

Borehole Support Testing A number of scouting experiments have been performed to provide a basis for understanding rock/EST interaction. In the following sub-sections, experiments relevant to the rock/EST interaction are presented. They include thick-walled cylinder tests with EST support and borehole collapse tests with inner hole pressure support. Expansion/Contraction behaviour of EST 18 16

External pressure (Bar)

14 12 10 8 6 4 2 0 0

1

2

3

4

5

6

7

8

To obtain an insight into the forces involved in EST expansion, a sleeve has been inflated around the EST. The pressure contraction response of the EST can be measured and it is shown below. Figure 115 shows the response of EST under several cycles of pressure loading and unloading. From the “stress-strain” curve, a value has been derived for the pressure response of the EST within its elastic range. It can been seen that the limit of the EST elastic behaviour is approximately 10 to 12 Bar.

Radial displacement (mm)

Figure 115: Change of EST Radius with external pressure General Sand Control Information Manual External Revision 1.0 - 125

TWC experiments with EST The thick wall cylinder (TWC) experiments involved installing an EST in an 85 mm outer diameter TWC sample with a 33 mm inner diameter hole and a length of 170 mm. The sample was then pressure tested in ROXELL with an outer rubber membrane isolating the sample from the cell’s pressurising fluid. Isotropic compressive pressure was applied on the outside (ie outer wall, top and bottom) of the sample while the inner hole was maintained at atmospheric pressure. The external pressure was applied incrementally. A rough indication of the inner-hole deformation was obtained by visual inspection using an endoscope placed within the hole. The external non-linear deformation was indicated through the pressure-volume response of the cell fluid. Sandstone test A 32% expanded EST was inserted into a Castlegate sandstone TWC sample. The external cell pressure was increased smoothly up to approximately 500 bars at which point the sample began to fail (see Figure 116). No prior indication of initial failure was indicated by the pressure curve, although visual inspection of the inner hole using an endoscope showed some break-out of sand grains at about 300 bars. Once the load capacity of 500 bar was reached, a pressure drop of 80 bar was observed, followed by a stage of post-failure ‘stabilisation’ in which the sample could withstand further pressure build-up to 690 bar (maximum allowable cell pressure). At this pressure the EST had deformed into an oval shape, but the slots were not fully closed. The additional stabilisation effect of the EST was established by comparison with an unsupported Castlegate TWC. Failure of the TWC without EST support occurred at approximately 300 bar, which is in agreement with previous Castlegate TWC tests It was observed that the EST support was able to keep the failed zone in place and hence, the composite structure sustained higher pressure than the TWC without EST support. Borehole collapse test The Borehole Collapse (BHC) test is essentially the TWC test with internal hydraulic support pressure. By comparing the BHC test to the TWC test with EST support, it is possible to express the EST support in terms of equivalent (mud) pressure support. The loading procedure of the BHC test is different from the TWC test. In the BHC test, the TWC sandstone sample is loaded hydrostatically to simulate in-situ stress condition by increasing the internal hole pressure Pin and external cell pressure Pex simultaneously, with rubber sleeves on both the internal and external of the sample. Subsequently, the external pressure is maintained while reducing the internal pressure at a constant rate. The inner hole pressure-volume behaviour is monitored for hole deformation and failure. In both the BHC test and the TWC test with EST, the inner holes are supported. In the former case, the inner hole is supported by fluid pressure and in the latter, by the expanded EST. Therefore, the BHC tests provide additional insights to the stabilisation effect of EST in the Castlegate Tests. The results of the BHC tests carried out on the Castlegate sandstone are summarised in Table 32. In these tests, various loading rates were used. The results are considered to be consistent and reproducible. The results show that with an inner hole support pressure as low as 10 bar, the TWC samples can withstand an external pressure of almost twice the TWC strength.


EST Supported Sandstone TWC External pressure (psi)

Up to 10,000 psi (max cell pressure) Ultimate Load capacity

7,250

Post failure stabilization

5,800

Some sand breakout observed using endoscope

4,350

TWC strength

2,900

TWC test TWC test with EST

1,450

5

10

15

20

25

30

Deformation (% cell vol.) Figure 116: Castlegate TWC testing with & without EST support

BHC Tests on Castlegate with Internal Pressure Test

Internal Pressure at Collapse (Bar)

External Pressure at Collapse (Bar)

1 2 3

14 16 10

680 680 680

Table 32: BHC testing


Loose-sand test Two thick-walled cylinder (TWC) experiments were also carried out with unconsolidated samples. In these experiments two fractions of loose sand were mixed and compacted around the EST which was wrapped in a mesh screen. An unconsolidated sand pack with 28% porosity was achieved in this way. With the support of the EST, the TWC loose-sand specimen sustained an external pressure of 80 bar before the slots of the EST started to close. This initial closure of the slots corresponds with the point where the pressure-volume curve deviates from linearity. This result was confirmed in a duplicate second test in which an endoscope was used to observe the slot closure. Analysis In order to assess the interaction between rock and EST, it is necessary first of all to describe the structural behaviour of the EST. The EST is a fairly complex structure with the capability to sustain a large strain deformation. An accurate description of EST and rock interaction under all load conditions and deformations (linear, non-linear, large strain) has not been completed. Instead a simplified model of the EST is adopted and, based on this model, the EST interaction with rock is studied using empirical as well as analytical methods. The analysis described in this section is used to consider the field application of the EST. To obtain an insight into the forces involved in EST expansion, a sleeve has been inflated inside the EST. The pressure-expansion response of the EST can be measured from the “stress-strain” like curve. In our present description of the EST behaviour, a number of assumptions are made. Linear elasticity is assumed so that the radial expansion and contraction of the EST are assumed to behave in an elastic manner (at least at relatively small strain). This is equivalent to assuming that at small strain, the EST would expand and contract like a flexible elastic tube without slots, and the EST has an equivalent elastic modulus, EC. The value of EC is obtained from the above experimental expansion of the EST. The EST also has an equivalent minimum yield pressure, which can be equated to the internal support pressure that the EST can provide without permanent deformation. In the above experiment, approximately 10 bar is needed for a radial elastic displacement of 0.35 mm. The minimum yield pressure can therefore be taken as 10 bar for this particular EST used in the tests. Rock-structure interaction Stresses and displacements in the rock surrounding the borehole and in the EST depend, not only on the rock mass properties and the in-situ stress field, but on the stiffness and deformation characteristic of the EST, ie the internal support pressure provided by the EST. A typical inner hole pressure response of the BHC test is shown in the figure below. This indicates the collapse of the sample at an inner hole pressure of between 10 and 16 Bar. Plotted in the same figure is the TWC test result with EST support. It should be noted that the loading path of the BHC test is not the same as that used in the TWC test. In the latter, the rock is not pre-stressed and an external pressure is applied incrementally until collapse. The inner support pressure can be empirically equated to the stiffness of the EST. Therefore stiff sets (those with high angle finger deformations and thick walls) will have a higher effective support pressure. The EST in the test has a minimum yield pressure of 10 bar, or an internal support pressure of 10 bar without permanent deformation.


20 18

Internal Pressure (Bar)

16 14 12 10

Castlegate BHC Test

8

Castlegate/EST Test

6 4 2 0 300

350

400

450

500

550

600

650

700

TWC (Bar)

Figure 117: Increase of Castlegate TWC strength with increasing internal pressure.

Internal borehole support effect on TWC A simple empirical assessment of hole stability can be made using the thick-walled cylinder strength. The instability of an open-hole horizontal well will occur if the effective vertical stress (or the greatest effective stress) is greater than the TWC strength (TWC). This can be expressed as:

The horizontal open-hole will be stable if σv / TWC < 1 The TWC test with EST support exhibited a higher load capacity. Denoting this ultimate load capacity as TWCE, the above empirical criterion can be modified as:

The horizontal open-hole with EST will be stable if σv / TWCE < 1 Since, from the test result; TWCE = 1.7 TWC The horizontal open-hole with EST support will be stable if σv / TWC < 1.7 This empirical criterion can be used in the assessment of EST field application. qualitative, especially when the factor of 1.7 is based on only limited data.

It is

If the results from the BHC test and the Castlegate test are plotted in terms of internal support at TWC strength, a straight line relationship can be derived. Similarly, the results from the loose sand EST test can be plotted on the same graph (see figure below). It is now possible to infer the effects of the EST on different ‘rock strengths’. General Sand Control Information Manual External Revision 1.0 - 129

18 16

Internal pressure (Bar)

14 12 10 8 Castlegate BHC Test

6

Castlegate/EST Test 4

Loose sand/EST Test

2 0 0

100

200

300

400

500

600

700

800

TWC (Bar)

Figure 118: Effect of internal pressure on increase in TWC of loose sand and Castlegate sandstone

Consider an example producing formation: The overburden stress has a value of 2.2 Bar/10m. The producing formation is at 3000m TVD and is hydrostatically pressured (1 Bar/10m). The effective stress governing material failure is σv, ie overburden stress less pore pressure. Initially, while the reservoir is undepleted, the maximum effective stress in the virgin formation is likely to be: σv

= ((2000)/10)x2.2 - ((3000/10)x1

σv

= 440 - 200

σv

= 240 Bar

The TWC strength of the material is 300 Bar for example. The formation is drilled and is stable (σv /TWC < 1). Consider now that the formation is allowed to produce and over time the virgin reservoir pressure is halved to 100 Bar. The unsupported formation will probably fail since σv /TWC = 1.13. Consider that the well had been installed with an EST after drilling with an internal support pressure of 10 Bar. The modified empirical criterion for an EST; σv /TWC < 1.7 and shows that the borehole would still be stable to the point of full depletion.

Benefits of borehole support in field applications In field applications some variation in borehole dimension is to be expected. Borehole support is achieved, in the case of solid cone and roller cone expansion as a result of surplus expansion as described above. The pre-requisites for successfully achieving this are: General Sand Control Information Manual External Revision 1.0 - 130

• •

Borehole ID variation within the limits determined by surplus expansion Accurate borehole geometry information to enable the optimum cone OD to be selected. The theoretical calculation tells us that if we use a 7.325” expansion cone, variation in wellbore ID between 8.375in and 8.744in can be accommodated. Ensuring complete borehole support with an ESS is highly dependent on being able to maintain the drilled hole diameter within these constraints. Experience with early ESS installations has shown that the choice of tool to determine borehole geometry can be of particular importance. Consider a typical four arm caliper used in dip tools. The stated accuracy for this tool is typically ±0.2in. Should the log show a minimum restriction of 8.5in in the open hole, it is possible that the actual minimum restriction is 8.3in. In this case a 7.375in OD cone could not be selected despite the log showing gauge hole. A smaller cone size would be selected to ensure that full expansion can be achieved, but the maximum hole ID limit for full support is reduced. An accurate borehole ID can be achieved by running an ultrasonic borehole imager such as a UBI, alternatively a caliper tool which has been proven to provide excellent results in ESS applications, is the 6 arm Diplog (STAR or FMS) which can provide a 3-D borehole image log. The plot below shows the actual results at one depth for a 4” ESS that has been deployed in 6” open hole. Following an open-hole UBI log, a 4.625” OD cone was selected for preinstalling into the top connector. The plot below shows an internal radius of 2.36” or 4.72” ID. Surplus expansion at this depth is only 2% and hence must be constricted by the formation. In conclusion borehole support was achieved. Further to that, a UBI log taken from a North Sea well following deployment and expansion of the ESS indicated that in the 12.25” rat-hole below the 9.625” casing shoe where the ESS was expanded without restriction, the internal radius was as much as 3.9” showing a surplus expansion of:

Surplus Expansion = ((3.9 x 2) – 7.125in [cone size]) / 7.125in [cone size] = 9.5 %. The remainder of the log in the 8.5” section showed surplus expansion between the range of 3 to 5 % indicating that full borehole support was achieved.


UBI Spiral Plot Shows Open Slots on High Side (Top)

UBI Borehole Radius @ 4690mMD

Figure 119: UBI log data illustrating borehole support


9. Support Services Technical & Operational Support Weatherford has many offices and facilities located around the world. Technical, commercial and operational support is available in the first instance from the nearest location. Sand control specialist personnel are located in Houston, Lafayette, Paris, Caracas, Rio de Janeiro, Aberdeen, Singapore and Kuala Lumpur. Technical and engineering support is also available from the Houston and Aberdeen. For wire-wrap based and Stratapac screens, additional offshore personnel and support are not normally required. However, personnel can of course be provided at the well-site as the situation demands. ESS currently requires an ESS crew to supervise the installation process, though less crew is required than for gravel packing. As rig crews become more experienced with ESS in say a field development, the number of ESS personnel needed would be expected to decrease. Onshore personnel and equipment are available to assist in the completion design, programme design, well planning and sand control selection strategy.

Sand Prediction & Production Technology Support Services are available to assist clients in making sand prediction calculations. The sand face completion is of course a critical component to the well and has a big impact on productivity. Computer modelling of the completion is required to ensure the well produces at an optimum rate by selecting the most appropriate equipment. Weatherford can provide such support services on a consultancy basis as and if required.

Engineering, Manufacturing and Service Support Conventional (eg Stratapac, Micro-Pak and Dura-Grip) screens are manufactured in five locations: New Iberia (Louisiana), Houston (Texas), Singapore, Batam (Indonesia) and Duri (Indonesia). ESS is manufactured in Aberdeen, UK. Manufacturing is performed to auditable and traceable standards. An Integrated Manufacturing Quality Plan (IMQP) can be provided at time of order in which the degree of in-process inspection, material traceability and documentation should be specified. Weatherford Completion Systems maintains a CNC and OCTG machine shop facilities at a number of locations world-wide for the manufacture of auxiliary equipment and the replacement/refurbishment of threads, etc. Weatherford is equipped to provide many additional services and equipment options, including: •

Expandable screens and borehole liners

•

Centralisation systems – bow-spring, solid rotating, roller options

•

Casing and tubing running crews and equipment

•

Liner hangers and EXP packers

•

External casing packers

•

Wash strings, seal bore subs and reaming shoes

•

Thru-tubing packers and equipment

•

Speciality products for zonal isolation, flow control & gravel packing.


Weatherford Sand Control Manual A4 R1

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