Chapter Managed Pressure Drilling Operations

Risk Assessment of Underbalanced and Managed Pressure Drilling Operations Mari Oma Engevik  May 31, 2007

1 of 3 Date

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2007-01-04

MAR/LMS

Faculty of Engineering Science and Technology Department of Production and Quality Engineering

MASTER THESIS Spring 2007 for stud. techn. Mari Oma Engevik

RISK ASSESSMENT OF UNDERBALANCED AND MANAGED PRESSURE DRILLING OPERATIONS (Risikovurdering av underbalansert boring og boring med styrt trykk (”managed pressure drilling”)) In recent years, underbalanced drilling (UBD) and managed pressure drilling (MPD) have been developed as alternatives to the traditional overbalanced drilling technique. The new techniques have several advantages, but the blowout risk is yet not fully understood. The main objective of the current master thesis is to develop a blowout risk model for UBD and MPD that is compatible with the  blowout frequency assessment model (BlowFAM) (BlowFAM) that has been developed by Scandpower. Scandpower. As part of this thesis, the candidate shall: 1. Give a detailed presentation of the technology and procedures that are used for UBD and MPD. The presentation shall be based on a detailed literature survey and contacts with drilling operators and their consultants. 2. Identify, describe and document hazardous events during the various steps of a UBD and an

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Master Master Thesis Spri ng 2007 for

Date

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2007-01-04

MAR/LMS

stud . techn. Mari Oma Engevik

Within three weeks after the date of the task handout, a pre-study report shall be prepared. prepared. The report shall cover the following: •

•

•

An analysis of the work task's content with specific emphasis of the areas where new knowledge has to be gained. A description of the work packages that shall be be performed. This description shall lead to a clear definition of the scope and extent of the total task to be performed. A time schedule for the project. The plan shall comprise a Gantt diagram with specification of the individual work packages, their scheduled start and end dates and a specification of  project milestones.

The pre-study report is a part of the total task reporting. It shall be included in the final report. Progress reports made during the project period shall also be included in the final report. The report should be edited as a research report with a summary, table of contents, conclusion, list of reference, list of literature etc. The text should be clear and concise, and include the necessary references to figures, tables, and diagrams. diagrams. It is also important that exact references are given to any external source used in the text. Equipment and software developed during the project is a part of the fulfilment of the task. Unless outside parties have exclusive property rights or the equipment is physically non-moveable, it should  be handed in along with the final report. Suitable documentation for the correct use of such material

3 of 3

Master Thesis Spri ng 2007 for

Date

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2007-01-04

MAR/LMS

stud . techn. Mari Oma Engevik

Responsible professor/supervisor at NTNU

Professor Marvin Rausand Telephone: 73 59 25 42 E-mail: [email protected]

Local supervisor at Scandpower Risk Management AS offices will be

Aexander Solberg, senior consultant Scandpower Risk Management AS P.O.Box 3  NO 2027 Kjeller Telephone: 64 84 45 43 E-mail: [email protected]

DEPARTMENT OF PRODUCTION AND QUALITY ENGINEERING

Asbjørn Rolstadås Professor/Head of Department

Preface This master thesis was has been written during the spring semester 2007, at the Norwegian University of Science and Technology, NTNU. The main objective of the master project was to developed a generic blowout frequency model for underbalanced and managed pressure drilling operations. The work was performed in cooperation with Scandpower, and the model developed was supposed to be compatible with their blowout frequency assessment model for conventional overbalanced drilling operations. According to the consulted companies, only two blowouts during MPD operations have occurred. Because of lack of data, it was not possible to develop a blowout frequency model. The focus of the thesis was therefore shifted toward a description of underbalanced and managed pressure drilling  technology, and various risk assessment methods and their use during these operations. It is assumed that the readers of this report have basic knowledge in drilling technology. I would like to thank my supervisors Professor Marvin Rausand at NTNU and Senior Consultant Alexander Solberg at Scandpower for their assistance during the preparation of this report. I  would also like to thank Michael Golan, Dave Samuelson, Per Holand, Arild Rødland, Alf Breivik, Harald Tveit, Johan Eck-Olsen for their contributions to this thesis.

Management summary  25% to 33% of all remaining undeveloped oil and gas reasources can not be utilized by means of  conventional overbalanced drilling. In addition, there are wells still containing oil and gas which could have produced more if alternative technologies to overbalanced drilling technology where utilized.Since 1990 underbalanced and managed pressure drilling has become increasingly used alternative technologies to conventional overbalanced drilling technology. With proper use these technologies may; eliminate or minimize formation damage, minimize costs related to the well, and increase safety during the drilling operations. However, the risk during these operations are  yet not known. During overbalanced drilling operations fluid from the reservoir is prevented from flowing into the well by a static mud pressure. This pressure is a result of the mud which is used during a drilling operation to carry cuttings from the formation to the surface. The pressure at surface is at atmospheric pressure. In underbalanced and managed pressure drilling, a lighter drill fluid can be used because a surface pressure is imposed. The main difference between overbalanced drilling and the alternative drilling technologies, is the use of a surface pressure during the drilling  operation. Numerous accidents have been documented with use of overbalanced drilling technology. By  evaluating earlier accidents and their cause, the risk these operations exposed to human, environment and assets, are fairly well known. In order to learn more about the risk during underbalanced and managed pressure drilling operations, earlier incidents should be collected and analyzed in a proper way. To collect data of well incidents during underbalanced and managed pressure drilling operations, authorities and companies in th U.S., Canada, and Norway were contacted. Only two incident have occurred, both with use of managed pressur drilling technology No reports were

drilling technologies were utilized. In overbalanced drilling operations, the probability of having an uncontrolled release of formation fluid is known. This is not the case for underbalanced and managed pressure drilling operations. By gathering information of the fluids flow rate through critical equipment during underbalanced and managed pressure drilling operations, the probability of release of formation fluids can be calculated. An uncontrolled release of formation fluids may occur if more than one of the  well safety equipment should fail to function properly. The probability of uncontrolled release of  formation fluid, can be calculated by combining the critical equipments probability.

Part 1 Introduction

Introduction During the last 17 years underbalanced drilling, UBD, and managed pressure drilling, MPD, have become increasingly used alternatives to conventional overbalanced drilling, OBD, technology. The new techniques provide several advantages, but the blowout risk during these operations is  yet not fully understood. Since the rotary drilling technology was introduced early in the last century, it has been the most used drilling technology in the oil and gas industry [2, 5]. The technique is well-established, and a number of well incidents have been documented. This has made the risk picture during OBD operations fairly well known. As forUBD and MPD operations the well incident data is limited, and the risk picture is not complete. Scandpower has developed a blowout frequency assessment model, BlowFAM. The model is a data tool for qualitative and quantitative safety evaluation of blowouts during OBD and well operations. BlowFAM reflects the actual elements; the technical, the operational and the organisational as well as reservoir conditions, that play an important role for the blowout risk. The program does not include UBD and MPD operations, and it is of interest to implement these techniques into the program. Few well incidents have occurred during UBD and MPD operations. Hazard analysis and risk  evaluations of well projects that utilize these technologies have been performed, but there has not been developed any worldwide accident investigation to state causal distributions and blowout statistics. Because there has been an increasingly use of UBD and MPD technology world wide, it is important to understand the risk during these operations. On the Norwegian continental shelf one UBD operation , and five MPD operations have been performed. In 2004, Statoil successfully performed an UBD operation on Gullfaks well C-05. One MPD operation was made by British Petroleum (BP) in the late 90’s by use of coiled tubing. Cono-

appendix..... The main objectives of the article in part two, are to a) give a technical description of UBD and MPD operations, b) identify hazardous events during a MPD operation, and c) perform an accident investigation with use of Haddon’s matrix and the 10 strategies on an OBD well incident.  A literature study has been carried out covered by relevant books, articles, Internet cites and by  attending a MPD course held by Statoil. Data collection has mainly been gathered by contacting  relevant companies, authorities and persons. In addition to this, searches on the Intrenet has been made. The master thesis has been performed over a period of 20 weeks. The main limitations during  this thesis has been; the availability of relevant data, and finding relevant literature.

Part 2 Hazard identification and SAFOP analysis of a MPD connection

Risk Assessment of Underbalanced and Managed Pressure Drilling Operations Mari Oma Engevik  May 31, 2007

1 Abstract Since 1990 underbalanced and managed pressure drilling have become increasingly used alternatives to conventional overbalanced drilling. The new techniques provide several advantages, but the blowout risk during these operations is yet not f ully understood. The main objective of this article is to evaluate the risk during underbalanced and managed pressure drilling operations.  With use of a continuous circulationsystem during a managed pressure drilling connection, the safe operability analysis revealed the blind ram as the most critical component. The continuous circulation system is a fairly new, and the operation requires special personnel. Communication, clear responsibilities, and good procedures are of great importance in order to prevent unwanted situations or to mitigate the consequences. Haddon’s matrix in combination with Haddon’s ten strategies, gives a detailed accident description and provides risk reducing measures to prevent future accidents. The method covers all socio-technical aspects, and does not require hands-on experience. In formations containing potential gas pockets; detailed pre-hazard analysis of the geotechnical properties of the specific area should be performed,

• increase safety during drilling operations The Underbalanced Drilling Sub-Committee [9] did in 1994 define UBD; "When the hydrostatic head of a drilling fluid is intentionally designed to be lower than the pressure of the formation being  drilled, the operation will be considered underbalanced drilling. The hydrostatic head of the drilling  fluid may be naturally less than the formation pressure or it can be induced. The induced state may be created by adding natural gas, nitrogen, or air to the liquid phase of the drilling fluid. Whether induced or natural, this may result in an influx of formation fluids which must be circulated from the well and controlled at surface." [13] The International Association of Drilling Contractors, IADC, subcommittee define managed pressure drilling, MPD, as; "An adaptive drilling process used to precisely control the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly" [27, 22]. UBD and MPD are used globally to drill new wells and to deepen or side-track from existing well bores [44]. UBD is as much a completion technology as it is a drilling technology [13]. During UBD and MPD the bottom hole pressure is lower than during OBD. In conventional OBD,  well control is performed by controlling the density of the drill-fluid. Because of the significant difference in friction and static pressure during OBD operations, friction pressure does not specifically  influence the bottom hole pressure. The pressure at the top of the mud columns is at atmospheric pressure and does not contribute to regulate the bottom hole pressure. As opposed to conventional rotary  drilling, UBD and MPD utilize surface pressure during the operations. The bottom hole pressure is controlled by a back-pressure choke which allows the use of lighter drill fluids. In UBD and MPD there are three ways to control the bottom hole pressure. It is done by controlling; the top pressure, the friction pressure (when fluid is circulated), and the static mud weight pressure. UBD and MPD utilize relatively light fluids with low static pressure and the circulated flow friction  will have a greater impact during these operations. The two main differences between UBD and MPD operations are the bottomhole pressure and the influx of formation fluid. In UBD operations, the bottomhole pressure is below the reservoir pore pres-

no reports of the accidents were found. The accident investigation is performed on a well drilled with use of OBD technology. This paper consists of three different parts. The first gives a technical description of UBD and MPD operations. In the second part a SAFOP is performed on a MPD connection operation, performed with use of CCS. The last part concerns accident investigation methods of UBD and MPD operations. An accident investigation is performed on a well incident during an OBD operation. The accident investigation is performed with use of Haddon’s matrix and Haddon’s 10 strategies to prevent harmful energy  of getting in contact with individuals or objects.

3 Underbalanced Drilling  Figure 1 illustrates the different bottom hole pressures with use of a low or high density drill fluid, and  with use of a low density drill fluid with top side pressure. We note that the top side pressure makes it possible to use light density drill fluids to achieve the wanted bottom hole pressure. By utilizing lighter density fluids, it is possible to drill sections with narrower drilling windows.

Figure 2: Pressure margins in OBD and UBD operations adapted from [21] sity. The liquid may however become compressible if it is mixed with formation hydrocarbon in the annulus of the well. With use of drilling mud, mud is pumped through the drill string as in conventional drilling. This kind of technology is limited to few particular cases of high formation pressure. It is used in formation where the pressure is rather high and the liquid is light enough to provide the desired UB conditions [21]. 2. Gaseated fluid; can either consist of a mixture of liquid and gas, or gas with liquid mist. - Mixture of liquid and gas. Gas is entrained in liquid mud which makes it lighter. The gas used can be; nitrogen, natural gas, air, and exhaust gas. The liquid can be water or oil based. Gasified mud can be introduced in two manners; surface mixing (introduced into the top of the drill string) or downhole mixing (introduced through parasite pipe string or parasite casing). This technology is used to drill in formations with low hydrostatic pressure. - Gas with liquid mist (wet gas). Basically gas drilling with injection of very small quantities of liquid in the gas stream. Typical mist systems have <2,5% liquid content. Mist flow is

3.1 UBD Equipment UBD operation can be conducted using a conventional drilling rig, or as a rig-less operation [21]. UBD operations may vary in equipment, fluid, procedures and purpose. Common for all UBDoperations are; the drilling operations are performedwith an UB pressure ratio, the wellbore at the top of the  well is sealed around the drill string while drilling and tripping, and the surface equipment is designed to remove formation fluid from the well and working area. UBD equipment systems are composed of all systems required to safely allow drilling ahead in geological formations with pressure at surface and under varying rig and well conditions. These systems include: the rig circulating equipment, the drill string, drill string non return valves, surface blowout preventer (BOP), control devices (rotating or non-rotating) independent of the BOP, choke and kill lines, UBD flow lines, choke manifolds, hydraulic control systems, UBD separators, flare lines, flare stacks and flare pits and other auxiliary equipment. The primary functions of these systems are to contain well fluids and pressures within a design envelope in a closed loop system, provide means to add fluid to the  wellbore, and allow controlled volumes to be withdrawn from the wellbore [44]. There are differentlayoutsand equipmentused depending of fluid in useand thedrillingsite. Figure 3 an example of a UBD systems flow loop is given. The system can be divided into a well system and a surface separation package system.

In UBD operations the top of the well is continuously pressurized and the drillstring has to rotate and move axially through the seal at the top of the well. A   rotating diverter  is used as a seal element in the annulus to allow rotation and movement of the drillstring. The rotating diverter is basically an annular BOP where the seal element is in constant contact with the rotating drill string and rotates together with the string [21, 36, 44]. There are basically two different rotating diverters [21, 36]; •  Rotating Control Head, RCH ; uses the elasticity of the rubber element with added energy from thewell pressure, to maintainthe seal aroundthe drill string. Itis a low pressure diverter, designed to rotate with drill pipe and used mainly in air drilling. • Rotating Blowout Preventer, RBOP; rotating annular preventer designed to rotate with pipe and seal on both pipe and kelly while allowing upward and downward movement of the pipe. It is energized by hydraulic pressure. Emergency Shutdown Valve refers to a remotely controlled, full opening valve that is installed on the flow line usually as near the BOP stack as possible [44]. 3.1.1 UBD surface equipment

The surface equipment during UBD operations may vary from use of simple rotating control device  with a combination of all or some of the UBD equipment listed below [15, 23, 10, 14]; • Rotating Control Device – RCD; maintains a dynamic seal on the annulus enabling chokes to control the annular pressure at the surface while drilling proceeds. • Downstream choke-manifold system; choke and choke manifold • Atmospheric or pressurized separation system including downstream fluid-separation package – 3-phase or 4-phase separation system

3.1.2 UBD subsurface equipment

 As mentioned earlier in section 3, there are three ways to inject fluid during UBD operations; through the drill string, a parasite string or a parasite casing. The downhole equipment in UBD consists of the following elements [21]; • Drill string  • Bottom hole assembly of the drill string  • String and wellbore isolation valves particular to the UB operations Drill string  There exist two categories of UBD drill strings which are;

• A conventional jointed drill string which has a full drilling rig scale, or • A small sized drill string or coiled tubing which respectively is methods for slim hole drilling and through tubing drilling. Bottom hole assembly  The bottomhole assembly with use of liquid based drilling mud is the same as in OBD, consisting of; drill bit, steer-able motors in cases with direction drilling, measure while dilling  andloggingwhile drilling packages. With use of other mediumin thedrill fluid special logging andmeasuring equipment needs to be used because of difficulties transmitting information as incompressible mud pulses through the drill string. A possible solution to this problem is to use low frequency electromagnetic signals which runs through the geological formations. String and wellbore isolation valves particular to UB operations String and wellbore isolation valves particular to UB operations are;

• Downhole check valves in the drill string prevent backflow into the drill string, enable light fluids

 working as a barrier. The primary barrier during UBD operations is made by a combination of flow and pressure control [5, 37]. The flow control system consists of; rotating control device, choke manifold, flowline, emergency shutdown valve (ESDV), and the surface separation system. In addition to this non-return valves (NRV) are installed in the bottom hole assembly and drill string to prevent flow up the drill pipe when a work string is run UB [5]. The secondary barrier during UBD operations is made by the BOP consisting of the wellhead connector and drilling BOP with kill/choke line valves.

3.3 Pro and Cons with use of UBD technology  Reservoir criteria which favor an UBD process: • Easily damaged reservoirs • Fractured reservoirs • Pressure Depleted reservoirs • Poorly understood complex geological formations • Prone to damage [14] • Hard rock [14] Drilling criteria which favor an UBD process: • Loss circulation potential. • Severe pressure depletion. • Poor ROP.

4 Managed Pressure Drilling  MPD has evolved since the mid-sixties [22], and is according to IADC subcommittee defined as; "adaptive drilling process used to precisely control the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly".[27, 22] The primary difference between conventional drilling and MPD is that in general MPD relies upon a closed circulating system whereby flow and pressure in the wellbore can be controlled [44]. The level of planning and actual equipment requirements for MPD depends on the specific technique, whether the application of the technology is for drilling enabling, reservoir damage reduction or reservoir characterization; whether hydrocarbons are present in the section being drilled, and in the case of drilling in the reservoir section, whether the intent is to produce hydrocarbons or not, the complexity and risk level associated with the section being drilled and finally, whether the well is onshore or offshore and deepwater or shallow water [44]. MPD is a form of drilling which allows greater and more precise wellbore pressure control than conventional drilling. The technology is suitable for wells with narrow margins. [7, 22, 15] The fluids used are non-compressible and as opposed to UBD, MPD does not invite influx of hydrocarbons. The technology exploits the opportunity to drill in a effective overbalanced state and makes it possible to  join pipes without interrupting circulation. [15, 34] The mud weight used will be lower than for the conventional mud weight and a secondary choke or frictional pressure will be applied on surface to create a combined annular pressure profile withing the well. [18] Compared with UBD MPD is better suited for drilling operations in severely depleted reservoirs  where there is a small margin between formation fracture and hole stability. [18] MPD provides advantages as to [22, 18, 14]; • Deeper open holes • Deeper, fewer, or smaller casings

4.1 MPD Technology  There two categories of MPD; 1.   Reactive when MPD technology is used on a well with conventional casing set points and fluid programs. 2.   Proactive the well is special designed for the MPD operation. Casing, fluids and open-hole program takes fully advantage of the MPD opportunities In addition to these two categories there exist variations of the MPD technology. In Marine environments there are said to be four main variations of MPD. The four variants each containing several under groups representing some differences e.g. variations in equipment [15, 22, 27]; • Constant Bottomhole Hole Pressure - e.g.Continuous circulation system (CCS), dynamic annular pressure control (DAPC), low density  drilling fluid (with choke valve for back pressure control), and Secondary annulus circulation using a mud with varying density. • Pressurized Mud Cap Drilling (PMCD) - e.g. Low riser return system (LRRS), and • Dual Gradient (DG) - e.g. Gas lift in riser (GLIR), equivalent circulating density reduction tool (ECDRT), and secondary  annulus circulation. • HSE or Returns Flow Control  Where constant bottom hole pressure, PMCD and HSE are the most commonly applied methods

loss zone. This allows lower density annular fluid (nitrogen gas can also be used in highly depleted sour gas zones) to be used and annular injection rate to be optimized. Annular pressure provides direct indication of what is happening down-hole; therefore, less fluid is lost to formation. Viscosifiers can be added to slow gas migration up the annulus. A rotating control device is a minimum requirement for pressurized mud cap drilling. Continuous Circulation Systems The fluid circulation system is designed such that thedynamicpressure profilein thewellbore is maintained duringthe drilling phase, including  connections. Low Head Drilling The low head drilling (LHD) technique is where the hydrostatic head of the wellbore fluid column is reduced to be either in balance or slightly greater than the formation pressure thus not planning to induce hydrocarbons or formation fluids into the wellbore. This can be accomplished using either a non-weighted low-density fluid or a gasified fluid. In addition, techniques (manual and automatic) are also available that allow drilling with an UB equivalent mud weight while maintaining balance or predetermined overbalance by use of flow control devices. [44]

4.2 MPD Equipment The surface equipment used in MPD operations may vary from just a rotating control device tied into the flowlines, to include one or more of the equipment mentioned below; • Choke which controls the back-pressure during the drilling operation, may be manually or automatically controlled • Surface separation package able to handle unwanted influx  The Rotating Control Device – RCD; maintains a dynamic seal on the annulus enabling chokes to control the annular pressure at the surface while drilling proceeds [10]. There exist three types of RCD systems [37]; 1. Passive systems; depends on the friction fit between the drill pipe and the rotating pack-off and  well bore pressure to affect the seal

• ballooning effects • Access to chromium [27] Should have a technological control device duringMPD in HPHT it is not a demand, but fora human to be intensed focus for several days is hard. MPD will likely improve the well control capabilities, combined with predictive modeling. MPD will probably require a smaller team and be done more quickly and to a lower cost than an UBD operation [27]. Mud cannot be considered as a barrier during MPD operations [27]. On installations consisting of subsea BOP with marine riser and telescoping slip-joints, the slip-joint  with typically be the weakest link in the riser system relative to pressure containment [15]. Better prepared for invasion of influx than conventional drilling technology. [15] If the the riser and choke system in a "closed loop" MPD operation is filled with gas, a fast and efficient down hole response is challenging. This problem is handled by CMC MPD operations [18]

5 Managed Pressure Drilling  MPD has evolved since the mid-sixties [22], and is according to IADC subcommittee defined as; "adaptive drilling process used to precisely control the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly".[27, 22] MPD is a form of drilling which allows greater and more precise wellbore pressure control than conventional drilling. The technology is suitable for wells with narrow margins. [7, 22, 15] The fluids used are non-compressible and as opposed to UBD, MPD does not invite influx of hydrocarbons. The technology exploits the opportunity to drill in a effective overbalanced state and makes it possible to

• No influx of formation fluids • Reduced chances of hydrate plugs forming at seabed • Extended bit life

5.1 MPD Technology  There two categories of MPD; 1.   Reactive when MPD technology is used on a well with conventional casing set points and fluid programs. 2.   Proactive the well is special designed for the MPD operation. Casing, fluids and open-hole program takes fully advantage of the MPD opportunities In addition to these two categories there exist variations of the MPD technology. In Marine environments there are said to be four main variations of MPD. The four variants each containing several under groups representing some differences e.g. variations in equipment [15, 22, 27]; • Constant Bottomhole Hole Pressure - e.g.Continuous circulation system (CCS), dynamic annular pressure control (DAPC), low density  drilling fluid (with choke valve for back pressure control), and Secondary annulus circulation using a mud with varying density. • Pressurized Mud Cap Drilling (PMCD) - e.g. Low riser return system (LRRS), and • Dual Gradient (DG)

Table 1: Different MPD technologies with areas of application and characteristics adapted from [15, 22] MPD technology

Area of Application

Characteristics 

CBHP

Narrow pressure environments

PMCD

Lost circulation issues Zones capable of consume drilling fluids and cuttings  Wells with grossly  depleted zones Deepwater drilling there. There exist long section of mud in the riser between seafloor and rig floor

Pipe connections made with surface pressure Not exceed fracture gradient during drilling  Process where heavy fluid is added. The amount of lost fluid is replaced with seawater, increasing ROP

DG

HSE

Typically on HPHT  wells Drilling on platforms where simultanious production is ongoing 

two different annulus fluid gradients

Closed mud return system on the rig floor

[27] Should have a technological control device duringMPD in HPHT it is not a demand, but fora human to be intensed focus for several days is hard. MPD will likely improve the well control capabilities, combined with predictive modeling. MPD will probably require a smaller team and be done more quickly and to a lower cost than an UBD operation [27]. Mud cannot be considered as a barrier during MPD operations [27]. On installations consisting of subsea BOP with marine riser and telescoping slip-joints, the slip-joint  with typically be the weakest link in the riser system relative to pressure containment [15]. Better prepared for invasion of influx than conventional drilling technology. [15] If the the riser and choke system in a "closed loop" MPD operation is filled with gas, a fast and efficient down hole response is challenging. This problem is handled by CMC MPD operations [18]

6 Comparison of UB, OB and MP drilling technologies MPD vs UBD [14]; 1. Because MPD operates with bottom hole pressure equal to or slightly higher than the pore pressure, the potential of hole collapse during UBD operations are greater. 2. Both UBD and MPD can reduce drilling-induced formation damage, but unlike MPD UBD has the potential to eliminate the formation damage. 3. Reduced equipment is usually required during MPD operations, e.g. need for separators capable of handling great amounts of mud, cuttings and formation fluids. 4. The production maximizing is greater for UBD operations than MPD operations because the for-

Production in the Kvitebjørn field has lead to lower fracture and pore pressure in the formation. Some places high pore-pressure zones are in the formation, leading to a narrow and difficult drilling   window to predict and drill [1]. For further development it will not be economical favorable, or in some cases even possible, to drill conventional. In order to cope with the difficult conditions at Kvitebjørn, MPD technology with use of a continuous circulation system, CCS, is planned. CCS utilizes a circulation system in order to join drill pipes to the drill string without interrupting  the drilling process [29, 40]. The potential benefits with use of CCS are [29, 31]; • Elimination of surges during start and stop of circulation • Continuous movement of cuttings in the annulus, no rig downtime to clean the bottom hole assembly  • Reduced total connection time • Reduced chance of stuck pipe during a connection • No downtime in HPHT wells to circulate out connection gas • Improved hole conditions • Improved control of equivalent circulation density  • Elimination of ballooning effects • Elimination of kicks while making connections CCS technology might benefit from OBD connection technology, but there might also be potential downsides. For Kvitebjørn this operation has never been performed before. With use of new technology there will always be a certain risk. In order to identify hazardous events, a SAFOP analysis was per-

Table 2: Description of equipment in CCS system adapted from [29] Equipment

Description 

Pipe guide Snubber

Guides the pipes in right position It’s object is to control movement of drill pipes into and out of the coupler. Operates with vertical and rotational forces and is connected to the coupler by four hydraulic rams. Uses hydraulic motors to spin the pipes into/out of connections and the hydraulic rams to apply make up or break out torque. A pressure chamber located on the rig floor over the rotary table. It seals around the drill pipe pin and box during the connection process. It consists of three pressure chambers; the upper with pipe rams, the middle with blind rams, and the lower with inverted pipe rams. Holds the pipe in position. Two are drain lines from the upper and lower coupler chamber and one is fill line into the lower chamber connected to the mud diverter manifold. Switches mud flow between the top drive and the coupler during drill pipe connections. It is connected into the discharge line between the mud pumps and the standpipe manifold.

Coupler

Pipe slips Flow paths

Mud diverter manifold

(a) Activate the pipe rams (b) Activate the pipe slips 3. Pressurize the chamber

Figure 4: The upper chamber is fully depressurized (Step 8 in the procedure) 12. Close the drain valve to the upper chamber 13. Pressurize the upper chamber 14. Open the blind ram 15. Connect the pipe joint and the drillstring  (a) Lower the pipe joint

Figure 6: Most risk contributing steps

8 Accident Investigation There exist various descriptions of the accident investigation process, depending on the author. The U.S. department of energy (DOE) divides the investigation process into three phases [12]; 1. Evidence and fact collection 2. Analysis of the collected facts 3. Conclusion, development of needs, and the report writing  This paper will focus on different methods to analyse data. There exist a great number of accident investigation methods, or techniques. Various methods are listed in table 3. Table 3: Accident investigation methods adapted from [17, 12]  Accident Anatomy Method  Action Error Analysis  Accident Evolution and Barrier Analysis

Events and Causal Factors Charting and Analysis Barrier Analysis Change Analysis

• investigate and evaluate the basis for potential criminal prosecution (blame) • evaluate the question of guilt in order to assess the liability for compensation (pay) Usually, major accidents are the result of multiple interrelated causal factors. Actors or decision makers influencing the normal work process might also affect accident scenarios directly or indirectly.  According to the DOE, the causal factors in an accident, can be divided into three different types [12]; • Direct cause; an immediate event or condition that caused the accident • Contributing cause; an event or condition that together with other causes increase the likelihood of an accident but which individually did not cause the accident • Root cause; the casual factor(s) that, if corrected, would prevent the recurrence of the accident The various methods scope, can be related to the socio-technical system involved in risk management. The different socio-technical levels are [42]; 1. the work and technological system 2. the staff level 3. the management level 4. the company level 5. the regulators and associations level 6. the Government level In appendix C, a presentation of the following four accident investigation methods is given; • Events and causal factors charting (ECFC) • Sequentially timed events plotting (STEP)

• the methods scope • no-hands on experience is needed • required resources

8.2 Accident investigation of well no. 6 at South Tambier block  The main objective is to convert an accident investigation into Haddon’s matrix and his 10 strategies. The result is dependent on the analysts understanding of the documented accident. The analysis of the collected facts seeks to find out what happened, when and where it happened, and why it happened. Haddon’s 10 strategies will give a list of actions that could have prevented the accident from occurring, or mitigated the consequences. The data collection was based on a prepared public accident report made by the MMS. During the first of December 2005, a loss of well control occurred in the conductor hole section on the South Timbalier Block Well No. 6 located on in the Gulf of Mexico. While drilling ahead beneath drive pipe in open water at a depth of 1,027 ft, there was observed a background gas reading of 224 units  with corresponding mud weight loss from 9.8 pounds per gallon to 9.6 pounds per gallon. Mud was  weighted up to 10.2 pounds per gallon, and drilling continued. The prescribed mud weight up schedule  was followed. At a depth of 1,318 ft in the conductor hole section, the well became unstable and released a pocket of gas. Personnel on the rig floor experienced that the gumbo box was overflowing. The driller immediately stopped the operation to undertake a flow check. Within minutes of this action, mud was seen flowing out of the rotary table. The well was placed on the diverter system. At the rig floor, it occurred flow from both of the diverter lines. One of the diverter valves placed at the rig floor, was closed because of the wind direction. Kill weight mud was circulated into the well. The well continued to "burp" gas over the next five days. Heavy weighted mud was circulated, while washing to bottom and back-reaming to prevent stuck pipe [47]. InFigure 7, theaccident is analyzedby use of Haddon’s matrix. Figure 7, gives a description of failure

investigation of UBD and MPD operations. In formations containing potential gas pockets; detailed pre-hazard analysis of the geothechniqal properties of the specific area should be performed, equipment capable of detecting the gas pockets as early as possible should be utilized, and alternative drilling technologies should be considered. For instance with use of UBD technology, separators capable of handling shallow gas, and formation fluids are utilized. The shallow gas would most likely not have caused any problems if this was an UBD operation. Recommendations to further work would be to; collect data on a world wide basis, and include an UBD and MPD profile in the SINTEF blowout database.

10 Acknowledgment I wouldlike to thank my supervisors Professor MarvinRausand at NTNU and Senior Consultant Alexander Solberg at Scandpower for their assistance during the preparation of this paper. I would also like to thank Michael Golan, Dave Samuelson Per Holand, Arild Rødland, Alf Breivik, Harald Tveit, Johan EckOlsen.

References [1] Leading edge advantages - statoil managed pressure drilling project. http://www.lealtd.com/statoilmanaged-pressure-drilling-project-c260.html , 16.03.2007. [2] Underbalanced drilling & near balance drilling in http://www.mms.gov/tarprojects/412/412%20AA.pdf  , 16.04.2007.

the

gulf

of

mexico.

[3] A probabilistic approach to risk assessment of managed pressure drilling in offshore drilling applications.   http://www.mms.gov/tarprojects/582.htm , 25.04.2007.

[12] DOE. Conducting accident incestigations doe workbook, second edition.  U.S. Department of Engergy, Washington D.C., USA , May 1999. [13] Alberta Energy and Utilities Board. Interim directive id 94-3, underbalanced drilling.  Alberta Energy and Utilities Board, Alberta, Canada , July 1994. [14] D. Finley, S. Shayegi, J. Ansah, and I. Gil. Reservoir knowledge and drilling – benefits comparison for underbalanced and managed pressure drilling operations. SPE/IADC Indian Drilling Technology Conference and Exhibition, presented at the SPE/IADC Indian Drilling Technology Conference  and Exhibition, Mumbai, India , October 2006. [15] K. Fisher and D. Hannegan. Managed pressure drillig in marine environments.   International  Petroleum Technology Conference, presented at the International Petroleum Technology Conference, Doha, Qatar , November 2005. [16] Center for Chemical Process Safety. Guidelines for investigating chemical process incidents, second edition. American Institute of Chemical Engineers, New York, USA , 2003. [17] Centre for Chemical Process Safety.  Guidelines for Investigating Chemical Process Incidents . 1992. [18] Børre Fossil and Sigbjørn Sangesland. Managed pressure drilling for subsea applications; well control challenges in deep waters.  SPE/IADC Underbalanced Technology Conference and Exhibition,presented at SPE/IADC Underbalanced Technology Conference and Exhibition, Huston, Texas, USA , October 2004. [19] R. Ekman G. Welander, L. Svanström. Safety promotion – an introduction, 2nd revised edition. Karolinska Institutet, Department of Public Health Sciences, Division of Social Medicine, Stocholm, Sweden , 2004. [20] A. A. Garrouch and H. M. S. Lababidi. Development of an expert system for underbalanced drilling 

[28] International Electrotechnical Commission (IEC). Iec 61882 hazard and operability studies (hazop studies) – application guide. International Electrotechnical Commission (IEC), Geneva, Switzerland , May 2001. [29] J. W. Jenner, H. L. Elkins, F. Springett, P. G. Lurie, and J. S. Wellings. The contionus circulation system: An advance in constant pressure drilling. Society of Petroleum Engineers Inc.,presented at  SPE Annual Technical Conference and Exhibition, Huston, Texas, USA , September 2004. [30] T. Kletz. Hazop and hazan : identifying and assessing process industry hazards . Institution of Chemical Engenieers, Warwickshire, UK, 1999. [31] Ø. Knutsen. Managed pressure drilling – a study of well control equipment.  Universitetet i Stavanger, Norway , June 2005. [32] J. C. O. Madsen. Identifikation af uheldsbelastede lokaliteter – antal eller alvorlighedsgrad?  Trafik forskningsgruppen Aalborg Universitet, Aalborg, Denmark , 2003. [33] J. McLennan, R.S. Carden, D. Curry, C. R. Stone, and R. E. Wyman. Underbalanced Drilling Manual . 1997. [34] E. H. Okstad. Drecision framework for well delivery processes – application of analytical methods to decision making. Department of Petroleum Engineering and Applied Geophysics, Norwegian  University of Science and Technology (NTNU), Trondheim, Norway , September 2006. [35] Hani Qutob. Underbalanced drilling; remedy for formation damage, lost circulation, and other related conventional drilling problems. Society of Petroleum Engineers Inc.,presented at Abu Dhabi  International Petroleum Exhibition and Conference, Abu Dhaib, UAE , October 2004. [36] J. Ramalho and R. Catchpole. Underbalanced drilling operations – hse planning guidelines.  International Association of Drilling Contractors, IADC , December 2002.

[46] D. Willis, F. Deegan, and M. J. Owens. Hazop of procedural operations.  Society of Petroleum Engineers,presented at the Second International Conference on Health, Safety & Environment in Oil &  Gas Exploration, Jakarta, Indonesia. , January 1994. [47] G. Woltman, L. Peterson, and T. Perry. Investigation of loss of well control south, timbalier block  135, well no. 6, ocs0463.  U.S. Department of the Interior, Minerals Management Service, New Orleans, USA , June 2006.

 A Safe operability analysis  A.1 Safe operability analysis history  SAFOP or procedure HAZOP is developed from the hazard and operability, HAZOP, analysis. HAZOP had its origin in 1963, developed by the Imperial Chemical Industries (ICI). The beginning of todays HAZOP was developed for use in assessing the hazards involved in the processes of chemical plants [30]. The process was based upon review of system piping and instrumentation diagrams (P&IDs). The method further developed to review the safety and operability of more complex activities [46]. Different needs and industries has lead to various HAZOP approaches; • Process HAZOP; technique originally developed to assess plants and process systems. • Human HAZOP; focuses on the human aspect and risk contribution rather than the technical failures. • Software HAZOP; Identifies possible errors in the development of software. • Procedure HAZOP or SAFOP (SAFe Operation Study); Evaluates procedures and operational sequences. The HAZOP analysis is usually performed on a process or operation in an early phase in order to influence the design. However it is also applicable on existing operations or processes to identify modifications that should be implemented in order to reduce risk and operability problems. It is a systematic and qualitative method based on guide words to identify deviations from the design intent [28]. The analysis is performed during a set of meetings by a HAZOP group consisting of; a leader, a secretary, and 4-6 technical experts [39, 38, 45]. In the traditional HAZOP analysis the guide words; NO, NOT, DON’T, MORE, LESS, OTHER THAN, PART OF andREVERSEare used. In addition there are guide words related to sequences as; EARLY, LATE BEFORE, and AFTER. These guide words may not be as applicable for all variations of HAZOP analysis

Table 4: Guide words in SAFOP et al B. Kirwan adapted from [38] Guide word Description   Unclear Step in wrong place  Wrong action Incorrect information Step omitted Step unsuccessful Interference effects from others

Column

No.  Work step Guide word Deviation Possible cause Consequences  Action required

Procedure is written in a hard way to understand and might be confusing  The procedure does not imply the correct sequence of  actions that should be made. The action presented in the procedure is incorrect Information that are checked prior to actions are incorrectly specified. Step not performed The step is performed incorrectly  The procedure performance is affected by other personnel carrying out simultaneous tasks

Table 5: Work sheet explanation Explanation   The SAFOP reference numbers. The studied step in the procedure. Guide words applied to the various steps. Deviation from the desired output of the step. The event causing the deviation. Possible consequences from the deviation. Pre-actions to prevent the deviation from occurring.

• The study generates extensive extensive information information • The analysis analysis is dependent on the the extent of the investigation investigation • Some team members members may dominate dominate more than others • It is not and "in-depth" review review of causes and consequences consequences • Does not consider consider common cause cause failures failures

B SAFO SAFOP P of conn connec ecti tion on wi with th use use of a cont contin inuo uous us cir circula culati tion on sy syst stem em

Study title:

Sheet:

Procedure title:

Revision No:

Date

Team composition

Meeting date

Part considered

Instruction step

No. 1

Deviation Pipes are in wrong position The pipes are not lifted Equipment and pipes are damaged

Step

2

3

  s   e   p    i   p    t    f    i    L  .    1

Guideword Unclear

Possible causes The position is written in a confusing way. Wrong equipment is used because of unclearance in the procedure. Wrong force is applied, or pipes are moved too fast due to a confusing procedure. Wrong action Pipes are left in wrong The wrong force is specified, position.Pipes are lost to the either the force given is too bottom of the hole. high or too low. The wrong equipment is specified. Incorrect information The pipes are lost, Wrong force might be applied, damaged or in wrong or the wrong positions are position. given. The equipment used does not the needed strength to lift the pipes in right position.

   #   e   y   c    t    l   n   y    i    i   e    t    b   e   a   u    f   q   a   r   e    S   e   p   s   n    O   o    C

Consequences 1 The operation is delayed 2 There are damage on the pipes 3 Equipment is damaged 4 Surges might occur 

Action required Find the position, speed, and tools that should be used during the lifting of the pipes, and make sure the procedure is clear and easy to understand.

# 1 2 3 4

S L M M H

O M M H H

1 Bit is damaged 2 Equipment is damaged 3 Pipes are damaged. 4 Surges might occur  1 Bit is damaged 2 Pipe rams are damaged 3 Pipes are damaged 4 Operation is delayed

Have a person check the procedures to make sure that the action stated in the procedure is correct. Review procedures and make sure right equipment, pressure and position is given.

1 2 3 4 1 2 3 4

L M L H L M L H

M H M H M H M H

The pipes are not lifted 1 Bit is damaged because the operation to lift the 2 Pipe rams are damaged pipes is not performed, or left 3 Pipes are damaged out in the procedure. Wrong action is performed by 1 Bit is damaged the personnel. 2 Pipes are damaged 3 Equipment is damaged

Train personnel and review procedure to make sure all the steps in the operation are included. Train personnel and make sure that the work environment is good.

1 L M 2 M H 3 L M

4

Step omitted

Pipes are left in wrong position.

5

Step unsuccessful

Pipes are left in wrong position. Pipes are lost downhole.

6

Interference effects from others

Pipes are left in wrong Operator is distracted, and fails 1 Bit is damaged position. The pipes are lost to make the right action. 2 Pipes are damaged downhole. 3 Equipment is damaged

1 L M 2 M M 3 M H

Train personnel and review 1 L M the work environment. 2 M M 3 M H

No. 7

Step

Consequences 1 Pipes are damaged 2 Equipment is damaged 3 Pipe rams does not support the pipes 4 The chamber is not sealed, which might lead to mud spill Step in wrong place Pipe rams are not closed, or The steps are in wrong 1 Pipes are not supported 2 they are closed before the sequnece in the procedure. Pipes are damaged pipes are lifted. 3 Equipment is damaged 4 The chamber is not sealed, which might lead to mud spill Wrong action Pipe rams are not closed, or Wrong action is given. The 1 Pipes are damaged closed too fast, too hard, or correct pressure is not 2 Pipe rams are damaged. too loose. specified, or the right terms are 3 Pipe rams does not not used. support the pipes 4 Chamber is not sealed, which might lead to mud spill

Action required Find right pressure, and speed that should be applied, and make sure they are clearly stated in the procedure.

# 1 2 3 4

S L M L L

O M H H M

Review procedure to make sure that the steps are in right order.

1 2 3 4

L L M L

H M H M

Find the right pressure, and speed that should be used, and make sure they are applied to the procedure.

1 2 3 4

L M L L

M H H M

10

Incorrect information Pipe rams are in wrong position

Review procedure before starting the operation.

1 M H 2 L M 3 L H

11

Step omitted

Review the procedure and train the operator.

1 L H 2 L H

8

9

  s   m   a   r   e   p    i   p   e    t   a   v    i    t   c    A    )   a    2

Guideword Unclear

Deviation Possible causes The pipe rams are not The right terms are not used in closed, or in wrong position. the procedure. The correct pressure is not specified in a clear manner.

Wrong pressure and positions 1 Pipe rams are damaged are given. 2 Pipes are damaged. 3 Pressure chamber is not sealed, which might lead to mud spill Pipe rams are not activated Operator does not activate the 1 Pipes are not supported. pipe rams, or it is not 2 The chamber is not documented in the procedure. sealed, which might lead to mud spill

No. 12

13

Step

  s   m   a   r   e   p    i   p   e    t   a   v    i    t   c    A    )   a    2

Guideword Step unsuccessful

Deviation Possible causes Pipe rams are not activated, Operator fails to perform the or they are in wrong position right action. The wrong amount of pressure is applied or the operator fails to leav the pipe rams in the right positions.

Interference effects from others

Pipe rams are left in the wrong position

The operator fails to take the right action because of distractions from co-workers.

Consequences 1 Pipes are damaged 2 Pipe rams are damaged 3 Chamber is not sealed, which may lead to mud spill. If the chamber leaks it might lead to; 4 mud loss 5 Kicks if pressure inside and outside the drillpipe is not equalized before disconnection is made 1 Pipe rams are damaged 2 Pipes are damaged. 3 Pressure chamber is not sealed, which might lead to mud spill

Action required Train personnel, and have an extra person to make sure the operation is performed correctly.

# 1 2 3 4 5

S L M L M H

O M H H L H

Review the procedure before performing the operation.

1 M H 2 L M 3 L H

No. 14

Step

15

16

17

  s   p    i    l   s   e   p    i   p   e    t   a   v    i    t   c    A    )    b    2

Guideword Unclear

Deviation Possible causes Pipe slips are not closed, or The terms used are unclear. they are in wrong position. The pressure is given in a confusing way.

Wrong action

Pipe slips are not closed, or The wrong action is given. they are in wrong position. Correct pressure is not specified. The right terms are not used.

Incorrect information The pipe slips are in wrong Wrong speed and pressure is position. specified in the procedure.

Step omitted

Pipe slips are not activated. Step is omitted in the procedure or by the operator .

Consequences 1 Operation is delayed. 2 Pipes are damaged. 3 Equipment is damaged. 4 Pipe slips does not support the pipes. 5 The chamber is not sealed. 1 Operation is delayed. 2 Pipes are damaged. 3 Pipe rams are damaged. 4 Pipe rams does not support the pipes. 5 The chamber is not sealed.

Action required Find the right pressure and speed, and apply the information to the procedures.

# 1 2 3 4 5

S L L M M H

O M M H H H

The procedure should be reviewed before the operation is started.

1 2 3 4 5

L L M M H

M M H H H

1 Equipment is exposed to unnecessary wear. 2 Equipment is damaged. 3 Pipe is damaged 4 Pipes are not supported 1 Pipes are not supported. 2 Pipes might be lost downhole or damaged when disconnected.

Review procedure before starting on the operation.

1 2 3 4

L M L M

M H M H

Review procedure before starting on the operation, and train personnel.

1 M H 2 M H

No. 18

19

Step   s   p    i    l   s   e   p    i   p   e    t   a   v    i    t   c    A    )    b    2

Guideword Step unsuccessful

Deviation Pipe slips are not in right position

Interference effects from others

Pipe slips are not in right position

Possible causes Consequences Incorrect action is taken. 1 Pipes are damaged Operator does not supply the 2 Equipment is damaged. 3 right amount of pressure, or the Pipe might be lost pipe slips are left in wrong downhole when position. disconnection is made Operator fails to take the right 1 Pipes are damaged action due to distractions 2 Equipment is damaged. 3 Pipes are not supproted, and might be lost downhole when disconnection is made

Action required Train personnel and have an extra person check on the operation.

# 1 2 3

S L M M

O M H H

Train personnel, and look at the work environment

1 L M 2 M H 3 M H

No. 20

21 22

Step

  r   e    b   m   a    h   c   e   z    i   r   u   s   s   e   r    P    3

Guideword Unclear

Deviation Possible causes Consequences Action required The valve to lower chamber The valve is not properly 1 The chamber might burst Control procedures before is not opened, or there is named, or the correct pressure if the pressure becomes too starting the operation. too much or too little flow . is not specified. high. 2 Operation is delayed. 3 Mud can be lost 4 Equipment is damaged. 5 Kicks might occur during disconnection if the chamber is not properly pressurized. Step in wrong place Valve is opened before the The sequence of operations is 1 Mud spill Review procedure before pipe rams are closed. wrong in the procedure action is taken. Wrong action Chamber is not pressurized, The wrong valve is specified to The perssure is not equal Review procedures before not fully pressurized, or over open in the procedure. The on the inside and on the starting the operation, and pressurized. flow rate given in the procedure outside og the drillstring. have an extra person is either too high, too low, or 1 Chamber might burst. cheking it. the wrong end pressure is 2 Operation is delayed. given. Pressure might be too high or too low which can lead to; 3 Mud loss. 4 Damage on equipment. 5 Kicks during disconnection.

# 1 2 3 4 5

S H L M M H

O H H L H H

1 L M 1 2 3 4 5

H L M M H

H H L H H

No. 23

24

25

26

Step

  r   e    b   m   a    h   c   e   z    i   r   u   s   s   e   r    P    3

Guideword Deviation Incorrect information Chamber is not fully pressurized, or it is pressurized too much.

Possible causes The wrong instruction and information is given in the procedure.

Consequences Action required The perssure is not equal Make sure the pressure on the inside and on the inside the drillstring is given outside og the drillstring. and review the pressures 1 Chamber might burst. before action is taken. 2 Operation is delayed. Pressure might be too high or too low which can lead to; 3 Mud loss. 4 Damage on equipment. 5 Kicks during disconnection. The pressure outside and Review procedure, and inside the drillstring is not control the pressure inside equalized. the chamber. Have an extra 1 Equipment is damaged. person checking. 2 Kicks might occur. 3 Operation is delayed. 1 Chamber might burst. Train operator, and have a Pressure outside and inside second person looking over the drillstring is not equal, the operation. Make sure which might lead to; there is good 2 Mud spill communication between 3 Mud loss or even the involved personnel 4 Kicks.

Step omitted

The chamber is not pressurized.

Step is omitted in the procedure or by the operator

Step unsuccessful

Chamber is not fully pressurized, or it is pressurized too much.

The chamber is not pressurized correctly by the operator.

Interference effects from others

Chamber is not fully pressurized, or it is pressurized too much.

Operator fails to take the right 1 Chamber might burst. Train personnel, monitor action due to distractions from Pressure outside and inside the pressure constantly, co-workers the drillstring is not equal, and review the work which might lead to; environment 2 Mud spill 3 Mud loss or even 4 Kicks.

# 1 2 3 4 5

S H L M M H

O H H L H H

1 M H 2 H H 3 L M

1 2 3 4

H L M H

H M L H

1 2 3 4

H L M H

H M L H

No. 27

Step

28

29

30 31

32

   t    i   n   u   g   n    i    b    b   u   n   s    t   c   e   n   n   o    C    4

Guideword Unclear

Possible causes Consequences Procedures are confusing and 1 Operation is delayed misleading. 2 Snubbing unit is damaged 3 Pipes are damaged Wrong action Snubbing unit is incorrectly Wrong instructions are given in 1 Delay connected. the procedure. 2 Damaged pipes 3 Damaged equipment Incorrect information Snubbing unit is incorrectly Wrong torque is applied, either 1 Equipment is damaged connected it is used too much or too little. 2 Pipes might be damaged

Step omitted Step unsuccessful

Interference effects from others

Deviation Snubbing unit is not connecte, or connected in the right way.

Snubbing unit is not connected. Snubbing unit is not connected the right way.

Step is omitted in the procedure or by the operator. Wrong action is performed by the operator.

1 Operation is delayed

1 Equipment is damaged. 2 Pipe is damaged. 3 Operation is delayed because it is not possible to disconnect the pipes. Snubbing unit is incorrectly The operator is distracted, and 1 Equipment is damaged. 2 connected. fails take the right action. Pipe is damaged 3 Operation is delayed because it is not possible to disconnect the pipes.

Action required Review procedures before the operations is started.

# 1 2 3

S L L L

O M H M

Have an experienced person checking the procedure. Make sure that the specifications given on pipe dimensions and torque are right before the operation is started. Review procedure

1 2 3 1 2

L L M M L

M M H H M

1 L M

Train personnel and double 1 M H check the operation. 2 L M 3 L M

Train personnel and make sure that the work environment is good.

1 M H 2 L M 3 L M

No. 33

Step

Guideword Unclear

Deviation The pipes are not disconnected, or they are damaged

34

Step in wrong place Disconnection is made before the chamber is pressurized.

35

Wrong action

36

37

  s   e   p    i   p    f   o   n   o    i    t   c   e   n   n   o   c   s    i    D    5

The pipes are not disconnected. Equipment and pipes are damaged. Incorrect information The pipes are not disconnected. Equipment and pipes are damaged.

Possible causes Consequences Procedures are insufficient as 1 Pipes are damaged. to what torque that should be 2 Equipment is damaged. 3 applied. Pipes might be Operation is delayed screwed in the wrong direction.

The wrong sequence given in the procedure.

1 Pipes are damaged 2 Equipment is damaged 3 Mud loss 4 Kicks The wrong torque is specified 1 Pipes are damaged in the procedure. 2 Equipment is damaged 3 Operation is delayed Too much or too little torque is 1 Pipes are damaged applied, or the pipes might be 2 Equipment is damaged. 3 screwed in the wrong direction Mud might be lost due to incorrect information in 4 Kicks may occur. the procedure.

Step omitted

The pipes are not disconnected.

Step is omitted in the procedure or by the operator

1 Operation is delayed because the pipes are not disconnected. 2 Pipes are damaged 3 Equipment is damaged if lifting is performed and the pipes are not disconnected.

38

Step unsuccessful

The operator fails to take the right action.

1 Pipes are damaged. 2 Equipment is damaged.

39

Interference effects from others

The pipes are not disconnected, or they are damaged The pipes are not disconnected, or they are damaged

Operator is distracted during 1 Pipes are damaged. the operation, and fails to take 2 Equipment is damaged. the right action.

Action required Review procedures before starting on the operation, and make sure the pressure outside the drillstring is equal to the one inside the drillstring. Review procedure before starting on the operation.

# 1 2 3

S L M L

O M H M

1 2 3 4 Check procedure before 1 the operation is started. 2 3 Make sure that the 1 pressure outside and inside 2 the drillstring is equal, and 3 that the right amount of 4 torque is given before action is taken. Review procedure and 1 have a second person 2 making sure the pipes are 3 disconnected.

L M M H L M L L M M H

M H L H M H M M H L H

L M L M M H

Train personnel.

1 L M 2 M H

Train personnel, and evaluate at the work environment.

1 L M 2 M H

No. 40

Step

41 42

43

44

  s   e   p    i   p   r   e   p   p   u    t    f    i    L    6

Guideword Unclear

Deviation Possible causes Pipes are in wrong position. Equipment that should have Equipment is damaged. been activated is not clearly specified. The end position of the pipes and the speed used to move the pipes with are not clearly defined. Step in wrong place The pipes are lifted before Wrong sequence is given in pipe ram is disconnected. the procedure. Wrong action Pipes are in wrong position. Wrong position is given in the procedure. Incorrect information Pipes are in wrong position. Wrong position is given in the Equipment and pipes are procedure. damaged.

Consequences Action required 1 Equipment is damaged. 2 Review procedures before Pipes are damaged. starting on the operation. 3 Operation is delayed.

# 1 2 3

S M L L

O H M M

1 Equipment is damaged 2 Pipes are damaged 1 Operation is delayed. 2 Equipment is damaged 3 Pipes are damaged 1 Equipment is damaged 2 Pipes are damaged

1 2 1 2 3 1 2

M L L M L M L

H M M H M H M

Review procedure before action is taken. Review procedures before starting on the operation. Review procedure before starting on the operation.

Step omitted

Pipes are not lifted.

Step is omitted in the procedure or by the operator.

1 Pipes are damaged if the Review procedure, and blind ram is closed. have an extra person to Lost control of the pressure check on the operation. downhole. The pressure might exceed/undergo the drilling window which might lead to; 2 Mud loss 3 Kicks

1 L M 2 M L 3 H H

45

Step unsuccessful

46

Interference effects from others

Upper pipes are in wrong position. Upper pipes are in wrong position.

Operator fails to take the right action. Operator is distracted, and fails to make the right action.

1 Pipes are damaged 2 Equipment is damaged 1 Pipes are damaged 2 Equipment is damaged

1 2 1 2

Train personnel Train personnel, and evaluate the work environment

L M L M

M H M H

No. 47

Step

48 49

50

   *   m   a   r    d   n    i    l    b   e   s   o    l    C    7

Guideword Unclear

Deviation Possible causes Blind ram is not closed, or it The terms used are unclear. is in the wrong position. The correct pressure that should have been applied is given in a confusing way.

Step in wrong place Blind ram is closed before the pipes are connected. Wrong action Blind ram is not closed, or it is in wrong position.

The wrong sequnece is given in the procedure. Wrong action or position is given in the procedure.

Incorrect information Blind ram is in wrong Wrong position and closure position, or the blind ram is pressure is given. damaged.

Consequences 1 Blind ram is damaged Blind ram does not seal between the upper and lower chamber which might lead to; 2 Mud loss 3 Kicks 1 Equipment is damaged 2 Pipes are damaged 1 Blind ram is damaged Chamber is not fully divided and sealed in two separate parts which might lead to; 2 Mud loss, or even 3 Kicks

Action required # S O Find the right pressure and 1 M H speed that should have 2 M L been applied, and make 3 H H sure that this is stated in a clear manner in the procedure. Review procedure before action is taken. Make sure the right positions are given before starting on the operation

1 Blind ram is damaged. Make sure that the right The chamber is not divided position and closure in two parts, and the blind pressure is given before ram does not seal between starting on the operation. the two separate parts. This can create wrong pressure downhole, which might lead to; 2 Mud loss or even 3 Kicks

* Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the snubbing unit dis lacement

1 2 1 2 3

M L M M H

M H H L H

1 M H 2 M L 3 H H

No. 51

Step

52

Guideword Step omitted

Step unsuccessful    *   m   a   r    d   n    i    l    b   e   s   o    l    C    7

53

Interference effects from others

Deviation Blind ram is open.

Possible causes The step is omitted in the procedure or by the operator

Consequences The chamber is not divided into two separate parts. This might lead to wrong pressure downhole and further to; 1 Mud loss, or even 2 Kicks Blind ram is not fully closed, The operator fails to leave blind Chamber is not divided into or it is damaged. ram in right position. two separate parts. The blind ram does not seal the chambers, which might lead to the wrong pressure downhole and further to; 1 Mud loss or even 2 Kicks

Action required Review procedure, and have an extra person to check the operation.

# S O 1 M L 2 H H

Train personnel and have a 1 M L second part to control the 2 H H operation.

Blind ram is not fully closed, Operator fails to take the right Chamber is not divided into Train personnel, and or it is damaged. action because of distractions. two separate parts. The evaluate the work blind ram does not seal the environment chambers, which might lead to the wrong pressure downhole and further to; 1 Mud loss or even 2 Kicks

* Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the snubbing unit dis lacement

1 M L 2 H H

No. 54

55

56

Step

  e   p    i   p    d   n   a    t   s    l   a   e    S    )   a    8

Guideword Unclear

Deviation Valve is not closed, or it is not fully closed.

Wrong action

Valve is not closed, or it is not fully closed.

Incorrect information Standpipe is not sealed

Possible causes Consequences Action required Description of the operation or 1 Operation is delayed. * Review procedures before marking of the valve is Mud continues flowing starting on the operation. insufficient in the procedure. through the standpipe and into the chamber. Too much pressure might lead to; 2 Leak through blind ram. 3 Leak of mud. 4 **Upper chamber might burst. The valve is marked wrong in 1 Operation is delayed. * Review procedures before the procedure. The wrong Mud continues flowing starting on the operation. closure pressure is given in the through the standpipe and procedure. into the chamber. Too much pressure may lead to; 2 Leak throgh blind ram. 3 Leak of mud. 4 Upper chamber might burst **.

# 1 2 3 4

S L M L H

O L H M H

1 2 3 4

L M L H

L M M H

Wrong pressure is given

1 L L 2 M M 3 L M

1 Operation is delayed. * Review closing pressure Mud continues flowing before action is taken through the standpipe and into the chamber. Too much pressure may lead to; 2 Leak in the blind ram 3 Leak of mud

* Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the  snubbing unit displacement ** Because of the amount of mud and pressure inside the chamber the consequences will be severe

No. 57

58

59

Step

  e   p    i   p    d   n   a    t   s    l   a   e    S    )   a    8

Guideword Step omitted

Step unsuccessful

Deviation Possible causes The standpipe is not sealed. The valve is not closed due to missing step in the procedure or because the step is omitted by the operator.

Consequences 1 Operation is delayed. * Mud continues flowing through the standpipe and into the chamber. Too much pressure might lead to; 2 Leak in blind ram. 3 Mud leak. 4 Upper chamber might burst. ** 1 Leak of mud. 2 Leak in blind ram.

Action required Review procedure, train operator, and have an extra person to check the operation.

The valve is not fully closed. Wrong action is taken by the Train personnel. operator. The person fails to close the valve completely. Interference effects The valve is not fully closed. Wrong action is taken by the 1 Leak of mud. Train personnel, and from others operator. The operator fails to 2 Leak in blind ram. evaluate the work fully close the valve because of environment. distractions * Operation is not delayed for a long time. The valves are rather easy to open and close leading to a lower operation cost than for e.g. the  snubbing unit displacement ** Because of the amount of mud and pressure inside the chamber the consequences will be severe

# 1 2 3 4

S L M L H

O L M M H

1 L M 2 M M 1 L M 2 M M

No. 60

61

62

Step   r   e    b   m   a    h   c   r   e   p   p   u   e    h    t   o    t   e   v    l   a   v   n    i   a   r    d   n   e   p    O    )    b    8

Guideword Unclear

Deviation Possible causes The chamber is not The drain valve in the depressurized, or not fully procedure is marked in a depressurized. The drain confusing way. Flow rate is not line is damaged.There is too specified clearly in the much flow through the drain procedure. valve.

Consequences Action required 1 Operation is delayed Make sure that the valve is Pressure is build up. Too marked in the same much pressure may lead to; manner in the procdure, 2 Leak of mud through the and on the control panel. blind ram Review procedure and 3 Mud spill specifications before action 4 Damage on equipment is taken.

# 1 2 3 4

Step in wrong place The pressure is not bled of Wrong sequence is given in before pipe ram is opened. the procedure.

1 Operation is delayed 2 Mud is spilled

Review procedures before starting on the operation.

1 L M 2 M M

Wrong action

1 Operation is delayed. 2 Damage on equipment 3 Mud spill

Review procedure and 1 L L make sure that the valve is 2 M H marked correctly, and make 3 L M sure that the right flow rate is given, before starting on the operation.

The chamber is not The valve is marked wrong. depressurized. There is too The flow rate is specified much flow through the drain wrong. valve.

S L M L M

O L M M H

No. 63

64

65

66

Step   r   e    b   m   a    h   c   r   e   p   p   u   e    h    t   o    t   e   v    l   a   v   n    i   a   r    d   n   e   p    O    )    b    8

Guideword Deviation Incorrect information The chamber is not depressurized.

Step omitted

The valve is in a closed position.

Step unsuccessful

The chamber is not depressurized, or there is too much flow through the drain valve. The chamber is not depressurized.

Interference effects from others

Possible causes The valve is not fully opened. The wrong amount of mud that is supposed to be drained is given. The valve is not opened due to missing step in the procedure, or because the step is omitted by the operator.

Consequences 1 Operation is delayed 2 Mud is spilled

Action required Review procedure before starting the operation.

# S O 1 L L 2 L M

1 Operation is delayed Review the procedure, and Pressure is build up. Too have a second person to much pressure may lead to; check that the valve is in 2 Leak of mud through the right position. blind ram 3 Mud spill 4 Damage on equipment

1 2 3 4

Operator fails to leave the valve in right position.

1 Operation is delayed. 2 Damage on equipment 3 Mud spill

Train the operator.

1 L L 2 M H 3 L M

Operator is distracted during the operation

1 Operation is delayed 2 Mud is spilled

Review the work environment, and train personnel.

1 L L 2 L M

L M L M

L M M H

No. 67

Step

68

69

70

Guideword Unclear

Possible causes The standpipe is not bleed of properly because the procedure does not give a clear description on how to perform the operation. Step in wrong place Standpipe is bled of before Wrong sequence is given in the drain valve is opened. the procedure.

Wrong action   e   p    i   p    d   n   a    t   s    f   o    d   e   e    l    B    )   c    8

Deviation There is mud in the standpipe.

There is mud in the standpipe.

Chamber is not pressurized properly, which might lead to; 1 Chamber bursting 2 Operation is delayed The amount of mud in 1 There is mud in the standpipe, and the dimensions standpipe. This might lead of the standpipe given in the to mud spill. procedure is wrong.

Incorrect information There is mud in the standpipe.

The wrong amount of mud is given in the procedure.

Step omitted

The standpipe is not bled off.

Step is omitted in the procedure, or by the operator

72

Step unsuccessful

There is mud in the standpipe.

73

Interference effects from others

There is mud in the standpipe.

71

Consequences 1 Mud is in the standpipe. This might lead to mud spill.

Action required Review procedures before starting on the operation.

# S O 1 L M

Review procedure before the operation is started.

1 H H 2 L H

Make sure the right 1 L M measures are made before starting on the operation.

1 There is mud in the Make sure the right standpipe. This might lead measures are given and to mud spill. applied to the procedure, before action is taken. 1 There is mud in the Review procedure and standpipe. This might lead calculations before taking to mud spill. action. Make sure that the pressure is fully bled off.

1 L M

Operator fails to take the right action.

1 There is mud in the Train personnel. standpipe. This might lead to mud spill.

1 L M

Operator fails to take the right action, because he is distracted.

1 There is mud in the Train personnel, and review 1 L M standpipe. This might lead the work environment. to mud spill.

1 M M

No. 74

Step

75

76

77

78

79

Guideword Unclear

Wrong action    t    i   n   u   g   n    i    b    b   u   n   s    t   c   e   n   n   o   c   s    i    D    )   a    9

Deviation Snubbing unit is not disconnected, or it is disconnected wrong. Snubbing unit is not disconnected correctly.

Incorrect information Snubbing unit is not disconnected correctly.

Possible causes The operation is not clearly specified in the procedure. The step specified in the procedure is wrong.

Incorrect information as to the pressure and operation is given in the procedure. Step is omitted in the procedure, or by the operator

Step omitted

Snubbing unit is not disconnected.

Step unsuccessful

Snubbing unit is not disconnected correctly.

The wrong action is taken.

Interference effects from others

Snubbing unit is not disconnected correctly.

Operator is distracted during the operation.

Consequences 1 Operation is delayed 2 Equipment is damaged 3 Pipes are damaged 1 Pipes are damaged 2 Equipment is damaged

Action required Check procedures and clarify the steps before starting on the operation. Check the procedure and make sure the steps are right before action is taken.

# 1 2 3 1 2

S L M L L M

O M H M M H

1 Damaged pipes 2 Damaged equipment

Check procedure before starting on the operation.

1 L M 2 M H

1 Operation is delayed If the pipes are removed before the snubbing unit is removed, there will be; 1 Damage on pipes 2 Damage on equipment 1 Damaged pipes 2 Damaged equipment

Review procedure and check, and make sure that the equipment is properly disconnected.

1 L M 2 L M 3 M H

1 Damaged pipes 2 Damaged equipment

Train personnel, and review 1 L M at the work environment. 2 M H

Train personnel, and 1 L M double check the operation. 2 M H

No. 80

Step

81

84

85

86

Deviation Upper pipe ram is not opened. Not opened fully

Consequences Not cleared from the pipe, or in wrong position, might lead to damage on; 1 Pipe 2 Equipment 1 Mud spill

Action required Check procedures and clarify the steps and pressures before starting operation

The wrong pipe ram is given in Not cleared from the pipe, the procedure or the wrong or in wrong position, might position is given. lead to damage on; 1 Pipe 2 Equipment Incorrect information Upper pipe ram is tightened. Pressure and position is Not cleared from the pipe, Not opened fully incorrect specified or in wrong position, might lead to damage on; 1 Pipe 2 Equipment Step omitted Upper pipe ram is closed Step is omitted in the Not cleared from the pipe, procedure or by the operator might lead to damage on; 1 Pipe 2 Equipment Step unsuccessful Upper pipe ram in wrong Operator fails to take the right 1 Pipe is damaged position action. 2 Pipe ram is damaged

Review procedure before starting operation

Step in wrong place Pipe ram is opened before the chamber is depressurized Wrong action Upper pipe ram is not opened. Not opened fully

82

83

Guideword Unclear

  m   a   r   e   p    i   p   r   e   p   p   u   n   e   p    O    )    b    9

Interference effects from others

Possible causes Not clearly specified in the procedure. Wrong ram is opened. Pressure given in an confusing way Wrong sequence in the procedure

# S O 1 L M 2 M H

1 H H

1 L M 2 M H

Review information given in 1 L M procedure, and make sure 2 M H they are right before action is taken. Review procedure and make check that the right position is achieved.

1 L M 2 M H

Train personnel, and 1 L M double check the positions. 2 M H

Pipe ram is not closed, or in Distraction leads to wrong pipe Not cleared from the pipe, wrong position ram is opened, or pipe ram is or placed in wrong position placed in wrong position might lead to damage on; 1 Pipe 2 Equipment

* If the pipe ram is damaged without being detected, kicks might occur. This is due to difficulties to maintain the right pressure inside the chamber.

1 L M 2 M H

87

88

89

90 91

  e   p    i   p   e   v   o   m   e    R    )   a    0    1

Unclear

Not in right position

Not clearly described in procedure

1 Equipment is damaged 2 Pipe is damaged 3 Operation is delayed

Wrong action

Pipes in wrong position

Wrong position is given.

1 Equipment is damaged 2 Pipe is damaged 3 Operation is delayed 1 Equipment is damaged 2 Pipe is damaged 3 Operation is delayed 1 Operation is delayed.

Incorrect information Pipes in wrong position

Step omitted Step unsuccessful

92

Interference effects from others

93

Unclear

94

95

96 97

  s    t   n    i   o    j   e   p    i   p   w   e   n    d    d    A    )    b    0    1

Wrong action

Pipe is not removed

Wrong pipes are added. Pipes in wrong position

Step unsuccessful

New pipe joints are not added Wrong pipes are added. Pipes in wrong position

Wrong pipes are listed in the procedure. Wrong position and dimensions are given in the procedure Wrong pipes are listed in the procedure Step is omitted in the procedure or by the operator Wrong actions are made

1 M H 2 L M 3 L M 1 2 3 1 2 3 1

M L L M L L L

H M M H M M L

M L L M L L M L L

H M M H M M H M M

1 Equipment is damaged 2 Pipe is damaged 3 Operation is delayed Operation is delayed

1 2 3 Make sure there is a good 1 work environment and train 2 personnel 3 Check procedures and 1 clarify the steps, equipment 2 and positions before 3 starting operation Review procedure and 1 make sure the right pipes 2 3 and positions is given before starting operation Review procedure 1 2 3 Train personnel 1

1 Equipment is damaged 2 Pipe is damaged 3 Operation is delayed

Train personnel, and make sure the communication is good

Step is omitted in the procedure or by the operator Pipes in wrong position Operator fails to take the right 1 Equipment is damaged action. 2 Pipe is damaged 3 Operation is delayed Pipes in wrong position Distraction leads the operator 1 Equipment is damaged to get pipes out of position 2 Pipe is damaged 3 Operation is delayed Wrong pipes. Not in correct What kind of pipes not clarified 1 Equipment is damaged position in the procedure. Not clearly 2 Pipe is damaged described in the procedure 3 Operation is delayed

Incorrect information Wrong pipes are added. Pipes in wrong position Step omitted

Wrong positions are given

Check procedures and clarify the steps and positions before starting operation Make sure the right positions is given before starting operation Review procedure information before action is taken Train personnel

1 Equipment is damaged 2 Pipe is damaged 3 Operation is delayed

Train personnel

M H L M L M M L L L

H M M L

1 M H 2 L M 3 L M

98

Interference effects from others

Pipes in wrong position Wrong pipes are added

99

Unclear

Ram is not closed Ram is not in right position Equipment is damaged Pipe is damaged

100

Step in wrong place Closed before pipes are in Step is listed in the procedure position in the wrong sequence Closed after the connection of snubbing unit

101

Wrong action

102

  m   a   r   e   p    i   p   e   s   o    l    C    )   a    1    1

Distraction leads the operator to get pipes out of position or fails to add the right pipes The terms used are unclear. Correct pressure is given in a confusing way.

1 Equipment is damaged 2 Pipe is damaged 3 Operation is delayed 1 Operation is delayed. 2 Pipes are damaged 3 Pipe rams are damaged 4 Pipe rams does not support the pipes, equipment is damaged 5 Chamber leaks if pressurized, leading to mud spill 1 Damage on pipes 2 Equipment is damaged

Make sure there is a good work environment and train personnel Find right pressure, and speed that should be applied, and apply to the procedures

1 2 3 1 2 3 4 5

Review procedure

1 L M 2 M H

Pipe rams are not closed. Wrong action is given. Correct 1 Operation is delayed. Find right pressure, and Closed too fast, too hard, or pressure is not specified. The 2 Pipes are damaged speed that should be too loose. right terms are not used 3 Pipe rams are damaged applied, and apply to the 4 Pipe rams does not procedures support the pipes, equipment is damaged 5 Chamber leaks if pressurized, leading to mud spill Incorrect information Pipe ram in wrong position Wrong pressure and positions 1 Pipe rams are damaged 2 Review procedures before are given Pipes are damaged. starting the operation. 3 Does not support the pipes, equipment is damaged 4 Pressure chamber is not sealed (may lead to mud spill)

M L L L L M M L

H M M M M H H M

1 2 3 4 5

L L M M L

M M H H M

1 2 3 4

L M M L

M H H M

103

Step omitted

Pipe ram is not activated

Operator does not activate the 1 Pipes are not supported, Review procedure and train 1 M H pipe ram or it is not equipment is damaged operator. Have an extra 2 L M documented in the procedure  2 The chamber is not person checking. sealed which may lead to mud spill

104

Step unsuccessful

Pipe ram is not fully closed

105

Interference effects from others

Pipe ram in wrong position

106

Unclear

Operator fails to leave pipe ram1 Pipe rams are damaged 2 Train personnel in right position. Pipes are damaged. 3 Does not support the pipes, equipment is damaged 4 Pressure chamber is not sealed (may lead to mud spill) Distraction from other 1 Pipe rams are damaged 2 Train personnel. View work operators leads to wrong Pipes are damaged. environment. action. 3 Does not support the pipes, equipment is damaged 4 Pressure chamber is not sealed (may lead to mud spill) Procedures are confusing 1 Operation is delayed. Review procedures before 2 Damage on equipment starting the operation 3 Pipes are damaged Step in wrong place in the 1 Damaged pipes Review procedure and procedure 2 Damaged equipment have an extra person 3 Mud spill looking over it before operation is started.

Snubbing unit is not connected. Not connected the right way. Step in wrong place Snubbing unit is not connected when the chamber is pressurized

107

108

Wrong action    t    i   n

Snubbing unit is connected Wrong instructions wrong

1 Damage on equipment 2 Pipes are damaged

Have an experienced person checking the procedure

1 2 3 4

L M M L

M H H M

1 2 3 4

L M M L

M H H M

1 2 3 1 2 3

L M M M M L

M H M M H M

1 M H 2 M M

109

Incorrect information Snubbing unit is not correctly connected

Wrong torque is applied, too much or too little.

1 Damage on equipment 2 Pipes are damaged

Step omitted

Snubbing unit is not connected

Step is omitted in the procedure or by the operator

1 Operation is delayed Review procedure If this is not detected before the chamber is pressurized this might lead to; 2 Equipment is damaged 3 Pipes are damaged 4 Mud spill

1 2 3 4

111

Step unsuccessful

Snubbing unit is not correctly connected

Wrong torque is applied, too much or too little.

1 Damage on equipment 2 Pipes are damaged

1 M H 2 M M

112

Interference effects from others

Snubbing unit is not correctly connected

Distraction from other 1 Damage on equipment operators leads to wrong action 2 Pipes are damaged

Train personnel and look at 1 M H the work environment 2 M M

113

Unclear

Valve is not closed Valve is not fully closed

Procedures are confusing. Valve marked in a confusing way

1 Delay because the drain valve is open or leaks

1 L L

Step in wrong place Valve is open when the chamber is pressurized Wrong action Valve is not closed Valve is not fully closed

Wrong sequence in the procedure Wrong thermology is used. Wrong position is given

Operation is delayed

Review procedures before starting the operation. Check pressure inside the chamber  Review procedure

1 L L

Incorrect information Valve is not fully closed.

The wrong positions and closuring pressures are given

1 Delay because the drain valve leaks

Review terminology and closing pressure before starting the operation. Check pressure inside the chamber  Review procedure, and check pressure inside the chamber 

110

114 115

116

  g   n    i    b    b   u   n   s    t   c   e   n   n   o    C    )    b    1    1

  r   e    b   m   a    h   c   r   e   p   p   u   o    t   e   v    l   a   v   n    i

1 Delay because the drain valve is open or leaks

Have an experienced person checking the procedure

Have an experienced person checking the procedure

1 M H 2 M M

L M M L

M M H M

1 L L

1 L L

117

  r    d   e   s   o    l    C    2    1

Step omitted

Valve is not closed

Step is omitted in the procedure or by the operator

1 Delay because the drain valve is open

Step unsuccessful

Valve is not fully closed.

Operator fails to leave the valve in right position.

1 Delay because the drain valve leaks

119

Interference effects from others

Valve is not fully closed. Valve is open

Operator is distracted, and fails 1 Delay because the drain to make the right action valve is open or leaks

120

Unclear

Valve in standpipe not opened Too much flow Too little flow Not the right pressure

Valve not properly named. 1 The chamber might burst Review procedures before Correct pressure is not 2 Operation is delayed. starting the operation. specified. Procedures are Pressure may be too high insufficient with respect to the or too low which during correct pressure. Can not verify connection might lead to; the right pressure 3 Mud loss 4 Damage on equipment 5 Kicks

1 2 3 4 5

H L M M H

H M L H H

121

Step in wrong place Chamber is not pressurized when blind ram is opened

122

Wrong action

1 Mud loss 2 Damage on equipment 3 Kicks Right valve is not specified to 1 The chamber might burst open. Flow rate is too high or 2 Operation is delayed. too low. Wrong end pressure is Pressure may be too high given. or too low which during connection might lead to; 3 Mud loss 4 Damage on equipment 5 Kicks

1 2 3 1 2 3 4 5

M M H H L M M H

L H H H M L H H

118

  r   e    b   m   a    h   c   r   e

Chamber is not depressurized. Not fully depressurized, or over pressurized

Review procedure, and 1 L L check pressure inside the chamber  Have a second person 1 L L checking the position of the valve Look at the work 1 L L environment

Review procedure

Review procedures before starting the operation, and have an extra person checking pressure in the upper chamber 

123

  p   u   e   z    i   r   u   s   s   e   r    P    3    1

Incorrect information Chamber is not fully The wrong instruction and pressurized, or pressurized information is given in the too much procedure

124

Step omitted

Chamber is not pressurized Step is omitted in the procedure or by the operator

125

Step unsuccessful

Chamber is not correctly pressurized

126

127

128

1 The chamber might burst Pressure may be too high or too low which during connection might lead to; 2 Mud loss 3 Damage on equipment 4 Kicks

1 Operation is delayed If the blind ram is opened before detection of the omitted step, this will lead to; 2 Mud loss 3 Damage on equipment 4 Kicks Operator fails to make the 1 Mud loss wrong action. The chamber is 2 Damage on equipment not correctly pressurized. 3 Kicks The operator is distracted, and 1 Mud loss fails to pressurize the chamber 2 Damage on equipment correctly 3 Kicks

Make sure the right pressure is given and review the pressures before action is taken

1 2 3 4

H M M H

H L H H

Review procedure. Control the pressure inside the chamber. Have an extra person checking.

1 2 3 4

L M M H

M L H H

1 2 3 1 2 3

M M H M M H

L H H L H H

Train operator and have a second part checking the operation Interference effects Chamber is not correctly Have a second part from others pressurized checking the operation, and look at the work environment Unclear Lower and upper chamber Blind ram is not opened. Not 1 Operation is delayed Check procedures and not connected, or not fully opened. Not clearly Chamber is still in an upper clarify the steps and connected in the right way specified in the procedure. and lower part. Not pressures before starting Pressure given in an confusing connected in the right way, operation way which might lead to; 2 Damage equipment 3 Damage on pipe Step in wrong place Blind ram is opened before Wrong sequence in the 1 Mud loss Review procedure the chamber is pressurized procedure 2 Damage on equipment 3 Kicks

1 L L 2 M H 3 M M

1 M L 2 M H 3 H H

129

Wrong action

130

131

132

133

  m   a   r    d   n    i    l    b   n   e   p    O    4    1

Blind ram is not opened. Wrong action or information is 1 Operation is delayed Upper and lower chamber is given in the procedure. Chamber is still in an upper not connected the right way and lower part. Not connected in the right way, which might lead to; 2 Damage equipment 3 Damage on pipe Incorrect information Blind ram is in wrong Wrong pressure and position is 1 Operation is delayed position. Blind ram is given in the procedure Chamber is still in an upper damaged and lower part. Not connected in the right way, which might lead to; 2 Damage equipment 3 Damage on pipe Step omitted Blind ram is not opened. Step is omitted in the 1 Operation is delayed procedure or by the operator Chamber is still in an upper and lower part, which might lead to; 2 Damage equipment 3 Damage on pipe Step unsuccessful Blind ram in wrong position Operator fails to leave the blind 1 Operation is delayed ram in right position Chamber is still in an upper and lower part, which might lead to; 2 Damage equipment 3 Damage on pipe Interference effects Blind ram in wrong position Operator is distracted, and fails 1 Operation is delayed from others to make the right action Chamber is still in an upper and lower part. Not connected in the right way, which might lead to; 2 Damage equipment 3 Damage on pipe

Control procedures before starting the operation.

1 L L 2 M H 3 M M

Control procedures before starting the operation.

1 L L 2 M H 3 M M

Review procedure, train operator 

1 L L 2 M H 3 M M

Train personnel

1 L L 2 M H 3 M M

Train personnel and look at 1 L L the work environment 2 M H 3 M M

134

Unclear

135 136

137

138 139

Step in wrong place    t   n    i   o    j   e   p    i   p   e    h    t   r   e   w   o    L    )   a    5    1

Wrong action

Incorrect information

Step omitted Step unsuccessful

140

Interference effects from others

141

Unclear

142

Step in wrong place

143

Wrong action

144

  s    t   n    i   o    j   e   p    i   p    t   c

Incorrect information

Pipes are in wrong position. Equipment that should be 1 Operation is delayed Pipes are moved too fast activated are not specified. 2 Equipment is damaged Position and speed is not 3 Pipe is damaged clearly defined. Lowered before the blind Wrong sequence in the 1 Pipe is damaged ram is closed procedure 2 Equipment is damaged Pipes in wrong position. Wrong position is given in the 1 Operation is delayed Pipes are moved too fast procedure. Wrong speed and 2 Equipment is damaged force is given. 3 Pipe is damaged Pipes in wrong position. Wrong position is given in the 1 Operation is delayed procedure. Wrong speed and 2 Equipment is damaged force is given. 3 Pipe is damaged Pipes are not lowered Step is omitted in the 1 Operation is delayed procedure or by the operator Pipes in wrong position. Operator fails to make the right 1 Operation is delayed action. 2 Equipment is damaged 3 Pipe is damaged Pipes in wrong position Operator is distracted, and fails 1 Operation is delayed to make the right action 2 Equipment is damaged 3 Pipe is damaged Pipes are not connected Procedures are insufficient as 1 Pipes leak properly. to torque that should be 2 Pipes are damaged. applied. Too much or too little 3 Equipment is damaged. 4 torque is applied. Operation is delayed Pipes are not connected Wrong sequence in the 1 Pressure decrease, and before the drain valve is procedure kicks might occur. opened Pipes are not properly Wrong torque is given in the 1 Pipes leak connected. procedure, too much or too 2 Pipes are damaged. little. Wrong rotation way is 3 Equipment is damaged. 4 given Operation is delayed Pipes are damaged Wrong force is specified. 1 Pipes leak 2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed

Review procedures before starting the operation.

Review procedures before starting the operation. Review procedures before starting the operation. Review procedure, train operator  Train operator

Train operator, and look at the work environment Review procedures before starting the operation.

Review procedure before starting the operation Review the procedure before the operation is performed Review the procedure before the operation is performed

1 L M 2 M H 3 M M 1 2 1 2 3 1 2 3 1

M M L M M L M M L

M H M H M M H M L

1 2 3 1 2 3 1 2 3 4 1

L M M L M M M M M L H

M H M M H M L M H L H

1 2 3 4 1 2 3 4

M M M L M M M L

L M H L L M H L

145

  e   n   n   o    C    )    b    5    1

Step omitted

Pipes are not connected

146

Step unsuccessful

Pipes are not properly connected.

147

Interference effects from others

Pipes are not properly connected.

148

Unclear

Valve is not closed Valve is not fully closed

149

Step in wrong place Valve to lower chamber is closed before blind ram is opened Wrong action Valve is not fully closed

150

151

  r   e    b   m   a    h   c   r   e   w   o    l   o    t   e   v    l

Incorrect information Valve is not fully closed.

Step is omitted in the procedure or by the operator

1 Operation is delayed. 2 Pressure downhole may increase and mud be lost. 3 If lower drain valve is opened, the pressure will decrease and kicks might occur. Operator fails to make the right 1 Pipes leak action. 2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed Wrong sequence in the 1 Pipes leak procedure 2 Pipes are damaged. 3 Equipment is damaged. 4 Operation is delayed Insufficient procedures and Flow of mud continues. marking of valves. May lead to a higher pressure than wanted; 1 Mud spill 2 Chamber might burst Wrong sequence in the Problems controlling the procedure BHP leading to kicks

Review procedure, train operator 

Wrong position is given

Review procedures before starting the operation. Keep an extra eye on the pressure inside the chamber  Review procedures before starting the operation. Keep an extra eye on the pressure inside the chamber 

Flow of mud continues. May lead to a higher pressure than wanted; 1 Mud spill 2 Chamber might burst The closuring pressure or Flow of mud continues. position is not correctly given in May lead to a higher the procedure pressure than wanted; 1 Mud spill 2 Chamber might burst

Train personnel, and have a second person checking

1 L L 2 M L 3 H H

1 2 3 4 Train personnel, and look 1 at the work environment 2 3 4 Review procedures before 1 starting the operation. Keep 2 an extra eye on the pressure inside the chamber  Review procedure 1

M M M L M M M L L H

L M H L L M H L M H

H H

1 L M 2 H H

1 L M 2 H H

152

  a   v   e   s   o    l    C    6    1

Step omitted

Valve is not closed

Flow of mud continues. Review procedures before May lead to a higher starting the operation. Keep pressure than wanted; an extra eye on the 1 Mud spill pressure inside the 2 Chamber might burst chamber. Train personnel Valve is not fully closed. Operator fails to make the right Flow of mud continues. Train operator, and always action. May lead to a higher keep an eye on the pressure than wanted; pressure inside the 1 Mud spill chamber  2 Chamber might burst Valve is not fully closed. Operator is distracted, and fails Flow of mud continues. Train operator, look at the to make the right action May lead to a higher work environment, and pressure than wanted; always keep an eye on the 1 Mud spill pressure inside the 2 Chamber might burst chamber  Chamber is not Valve in procedure is marked 1 Operation is delayed Check marking and review depressurized. Not fully in a confusing way. Flow rate is Pressure build up. Too procedure and depressurized. Drain line is not specified, opening in valve much pressure may lead to; specifications before damaged. Too much flow not specified 2 Leak of mud through the operation is started blind ram 3 Mud spill 4 Damage on equipment

153

Step unsuccessful

154

Interference effects from others

155

Unclear

156

Step in wrong place Depressurize of the chamber starts before the connection is made Wrong action Chamber is not depressurized. Too much flow

157

  r   e    b   m   a    h   c    f   o    d

Step is omitted in the procedure or by the operator

1 L M 2 H H

1 L M 2 H H

1 L M 2 H H

1 2 3 4

L M L M

L M M H

Wrong procedure sequence

2 Kicks

Review procedure before the operation is started.

1 H H

Valve is not correctly marked. Flow rate specified wrong, diameter opening in valve is too small or too wide in the procedure

1 Operation is delayed. 2 Damage on equipment 3 Mud spill

Review procedure and make sure valve is marked in the right way in the procedure, and right pressure for the drain line and opening of the valve is given before starting operation.

1 L L 2 M H 3 L M

158

  e   e    l    B    7    1

Incorrect information Chamber is not depressurized

Valve is not fully opened. 1 Operation is delayed Wrong amount of mud is given 2 Mud is spilled

159

Step omitted

Valve is not opened

The valve is not opened due to 1 Operation is delayed Review procedure and missing step in the procedure Pressure build up. Too have a second person or omitted step by the operator  much pressure may lead to; checking. 2 Leak of mud through the blind ram 3 Mud spill 4 Damage on equipment

160

Step unsuccessful

Operator fails to leave the valve in right position.

161

Interference effects from others

Chamber is not depressurized. Too much flow Chamber is not depressurized

162

  e   v    l   a   v   n    i   a   r    d   e   s   o    l    C    8    1

163

164

165

1 L L 2 L M 1 2 3 4

L M L M

L M M H

1 2 3 View the work environment 1 and train personnel 2

L M L L L

L H M L M

Train operator

Step in wrong place Drain valve is closed before Wrong sequence in the the chamber is procedure depressurized.

Pressure builds up. Too Review procedure before much pressure may lead to; starting the operation 2 Leak of mud through the blind ram 3 Mud spill 4 Damage on equipment

1 M M 2 L M 3 M H

Unclear

1 Operation is delayed 2 Damage on equipment 3 Damage on pipes 1 Damaged pipes 2 Damaged equipment

Check procedures and clarify the steps before starting operation Check procedure and make sure the steps are right before action is taken

1 2 3 1 2

1 Damaged pipes 2 Damaged equipment

Check procedure before starting the operation.

1 L M 2 M H

Wrong action    t    i   n   u   g   n    i    b    b   u   n   s

Operator is distracted during the operation

1 Operation is delayed. 2 Damage on equipment 3 Mud spill 1 Operation is delayed 2 Mud is spilled

Review procedure before starting operation

Snubbing unit is not disconnected, or not disconnected right Snubbing unit is not disconnected correctly

Not clearly specified in the procedure. The steps are wrong

Incorrect information Snubbing unit is incorrectly Incorrect information of disconnected pressure and procedure

L M L L M

M H M M H

166

  c   e   n   n   o   c   s    i    D    9    1

Step omitted

Snubbing unit is not disconnected.

Step is omitted in the procedure or by the operator

167

Step unsuccessful

Wrong action is taken.

168 169

Interference effects from others Unclear

170

Wrong action

Snubbing unit is not disconnected correctly Snubbing unit is not disconnected correctly Pipe slips are not disconnected, or not disconnected right Pipe slips are not disconnected correctly

171

  s   p    i    l   s   e   p    i   p    t   c   e   n   n   o   c   s    i    D    0    2

Operator is distracted during the operation Not clearly specified in the procedure. The steps are wrong

1 Operation is delayed If the pipes are removed before snubbing unit is removed, it will be 2 Damage on pipes 3 Damage on equipment 1 Damaged pipes 2 Damaged equipment 1 Damaged pipes 2 Damaged equipment 1 Operation is delayed 2 Damage on equipment 3 Damage on pipes 1 Damaged pipes 2 Damaged equipment

Review procedure and 1 L M check that the equipment is 2 L M disconnected. 3 M H

Train personnel, double check operation. Train personnel, and look at the work environment Check procedures and clarify the steps before starting operation Check procedure and make sure the steps are right before action is taken

1 2 1 2 1 2 3 1 2

1 L M 2 M H

L M L M L M L L M

M H M H M H M M H

Incorrect information Pipe slips are incorrectly disconnected

Incorrect information of pressure and procedure

1 Damaged pipes 2 Damaged equipment

Check procedure before starting the operation.

Step omitted

Pipe slips are not disconnected.

Step is omitted in the procedure or by the operator

Review procedure and 1 L M check that the equipment is 2 L M disconnected. 3 M H

173

Step unsuccessful

Wrong action is taken.

174

Interference effects from others Unclear

Pipe slips are not disconnected correctly Pipe slips are not disconnected correctly Pipe rams are not opened. Not opened fully

1 Operation is delayed If the pipes are removed before pipe slips are removed, it will become; 2 Damage on pipes 3 Damage on equipment 1 Damaged pipes 2 Damaged equipment 1 Damaged pipes 2 Damaged equipment 1 Damaged pipes 2 Damaged equipment

172

175

Operator is distracted during the operation Not clearly specified in the procedure. Pressure given in an confusing way

Train personnel, double check operation. Train personnel, and look at the work environment Check procedures and clarify the steps and pressures before starting operation

1 2 1 2 1 2

L M L M L M

M H M H M H

176

Step in wrong place Not opened before the Wrong sequence in the procedure continues. procedure Opened before the pressure is bled off 

1 Damaged pipes 2 Damaged equipment 3 Mud spill

Review procedure and 1 L M monitor the pressure inside 2 M H the chamber  3 M M

Wrong action

Wrong position is given in the procedure.

1 Damaged pipes 2 Damaged equipment

Review procedure before starting operation

1 L M 2 M H

Incorrect information Pipe rams are tightened. Not opened fully

Pressure and position is incorrect specified

1 Damaged pipes 2 Damaged equipment

1 L M 2 M H

179

Step omitted

Pipe rams are closed

Step is omitted in the procedure or by the operator

1 Damaged pipes 2 Damaged equipment

180

Step unsuccessful

Pipe rams in wrong position Operator fails to make the right 1 Damaged pipes action. 2 Damaged equipment

Review information given in procedure, and make sure they are right before action is taken. Review procedure and make check that the right position is achieved. Train personnel

181

Interference effects from others

Pipe rams in wrong position Operator fails to make the right 1 Damaged pipes action, because of disturbing 2 Damaged equipment factors

177

178

  s   m   a   r   e   p    i   p   n   e   p    O    1    2

Pipe rams are not opened. Not opened fully

1 L M 2 M H 1 L M 2 M H

Train personnel and look at 1 L M the work environment 2 M H

C Description of various accident investigation methods C.1 Events and causal factors charting  Events and causal factors charting (ECFC) is a method to identify multiple failure causes. It gives a graphical illustration of event sequences necessary and sufficient for an accident to occur. The method is used to determine causal factors by identifying events and conditions that lead to the accident. Figure 10 presents symbols and guidelines used to prepare the events and causal factors chart. An illustration of the chart is given in figure 11. The elements used in this illustration, are explained in figure 10. The graphing is a dynamical process to ensure that the investigation is done in a best possible manner, and that the investigators have a clear representation of accident chronology for use in evidence collection and witness interviewing [12].

C.2 Sequentially timed events plotting  STEP was developed in 1987 by Hendrick and Benner. The method is a multi-linear method, with parallel time bases. Different activities, performed by different actors, can take place at the same time. An actor is a person or an item that directly influence the flow of events leading to an accident. The investigation follows a process view and consists of a STEP-worksheet illustrating different events that occur and the time they take place, see figure 12 [42].

Figure 12: Illustration of a STEP-worksheet, adapted from [42]  Arrows combine the different event relations in the accident chain. The arrow gives an overview of  the events leading to an accident. The STEP-method also includes the following truth-testing procedures [42]; 1. The row test, which makes sure each actor is broken down sufficiently and that all the events are included. 2. The column test, which makessure the sequences of eventsare paired with the relevant actions of 

The first two elements listed above, results in an event and cause chart, the third is a barrier analysis and the fourth is a change analysis. For further explanation of barrier and change analysis see [42]. The method starts by identifying the chain of events and illustrate these in a block diagram. Further the analyst should identify possible technical and human causes for each event and dedicate these vertically to the relevant events in the diagram, see figure 13. After this is done a barrier analysis of  technical, human and organisational barriers that have failed, or were not present, should be listed. These are illustrated and placed on the bottom of the worksheet, see figure 13. Deviation description is the last step that is performed. The deviations and the normal situation is illustrated at top of the event and cause chart [42].

C.4 Haddon’s Matrix  Haddon’s matrix was developed by W. Haddon in the 1970’s, and is a process method. Accidents are described as a chronological sequence of events [43]. The method was developed for traffic accidents,  where the accident was revealed as a result of system failure between driver (human), vehicle (machine), and road and surroundings (environment). The method evaluates the system failures according to an accidental time axis. This axis is divided into; before, during, and after the event occurred [32]. Haddon’s matrix consist of columns representing the three different system failures, and the rows represent the accidental time axis [43, 19]. The method is used mainly to map the accident. By combining the matrix   with Haddon’s accident prevention strategies the method can be used for both preventive precaution and minimization of possible consequences if an accident should occur [32]. The accident preventionstrategiesare based on the"energy - barrier model". The modelis a strategy  to prevent harmful energy getting in contact with individuals or objects. The 10 strategies are listed below, copied from [24]; 1. Prevent the build-up of energy  2. Modify the characteristics of the energy  3. Limit the amount of energy  4. Prevent the uncontrolled release of energy  5. Modify the rate and concentration of the energy  6. Separate the source of energy and the potential victim in time or space 7. Separate by means of physical barriers 8. Improve the target’s ability to endure an energy flow 

Part 3 Data collection and a quantitative approach of blowout frequencies during UBD and MPD operations

1 Data collection To collect well incident data during UBD and MPD operations, authorities and companies in the U.S., Canada, and Norway, were contacted. To develop a frequency assessment model for UBD and MPD operations, collection of well incidents during these operations were of interest. By analyzing accident reports, accident contributing factors along with reservoir characteristics could have been identified. A model could have been developed on behalf of these facts, which would have contributed to a better risk understanding of UBD and MPD operations. In table 1 a list of persons that have contributed information to this paper is given.

Contact person

Table 1: List of contacts E-mail address

Per Holand Dave Samuelson Don Buckland Melinda Mayes Mildered Williams Murray P. Sunstrum

[email protected] [email protected] [email protected] [email protected] [email protected] [email protected]

Company   Exprosoft EUB OGC MMS MMS Enform

Per Holand, at Exprosoft, is responsible of frequently updating a blowout database owned by  SINTEF. This database documents blowouts and well releases world wide. According to him, no blowouts are recorded in the database during UBD or MPD operations. Accident investigation reports from 2003 until present were examined, but no well incidents with use of UBD or MPD technology was found.

2006, only 175 applicants indicated they would be conducting UBD operations. The actual number is expected to be much higher due to rate of penetration application, and air drilling for barefoot completions. Barefoot completions are open hole completions, which are very common for the Canadian sweet shallow gas targets. In a period from 2001-2006, the total amount of wells drilled in Alberta were 106 600 according  to the Canadian Association of Petroleum Producers (CAPP) [6]. EUB’s official number for the same period is 103 163. The number of wells drilled in this period, does not correspond to the CAPP’s number due to a variety of reasons such as; reentries, resumption of drilling, spud timing (a well might be spudded one year, while the rig is released the followingyear) etc., but they are reasonably  close. The number of spuds EUB have for 2002 and 2003 is respectively 13 193, and 17 108. It was not stated how many of these that were drilled with use of MPD.

2 A quantitative approach of blowout frequencies during UBD and MPD operations  An other way to quantify the blowout risk during UBD and MPD operations is to look at uncertainties related to the fluid flow rate. Fluid flows through a variety of equipment. A blowout might occur if critical equipment in the process is incapable of handling the fluid rate. The probability of  a blowout can be calculated by establishing the probability of exceeding critical equipments fluid rate capacity. For instance may the separators flow rate capacity be exceeded. Figure 1 illustrates the fluid flow from the well into the separator.It is possible to look at reservoirs containing oil, gas and water. To simplify, this discussion will only consider a reservoir containing a low compressible fluid.

q  =  J ( p R  − p w ) =  J ∆p 

(1)

p R  is the reservoir pressure, p w  is the bottom hole pressure in the well, and J is the productivity  index. The productivity index for oil is given in equation 2. To account for a mixture of liquids, the productivity index must be modified.  J o  =

2πkh   r  µo B o (l n  e  r w 

−

3 4)

(2)

k  is the permeability, h  is the formation thickness, µo  is the oil viscosity, B o  is the oil formation volume factor (oil shrinks on the way up), r e  is the external drainage radius of the well, and r w  is the wellbore radius. It is assumed pseudo steady state, which is applicable for the beginning phase of the production [3]. The maximum rate a specific separator can handle, q ma x , is known. This gives the maximum pressure drawdown, ∆p ma x ; ∆p ma x  =

q ma x   J 

(3)

It is assumed that ∆p ma x  does not exceed the pressure difference between the hole collapse pressure and the pore pressure. If this had been the case, the hole would have collapsed before the separator capacity was exceeded. There are uncertainties related to the bottom hole pressure in the wellbore and in the formation pressure. These might be a result of for instance inaccuracies in the measuring equipment and in the geological estimation of the pore pressure. The uncertainty related to the permeability,  k , in equation 2, is disregarded in this paper. The productivity index is assumed constant.

Pr ((P  f   − P w ) < or  = 0)

(7)

In addition to the flow rate, equipment might have constraints to fluid pressures. The maximum pressure, p ma x , equipment can handle, is known. The top pressure is given in equation 8. 1 ρ p t  = p w  − ρ g h −  f   v 2 2 d 

(8)

p t  is the top pressure,  ρ  is the mud density, g  is the gravity force, f    is the friction force, and d  is a combination of the well diameter and the annulus diameter [1].  Where the velocity, v , is given by; q  2q  v  = = (9)  A  πd 2  A  is the areal in the annulus. Equation 8 and 9 gives; ρ 1 p t  = p w  − ρ g h −  f   5 2 q 2 h  2 d  π

 

(10)

 A blowout might occur if the top pressure exceeds the max pressure of critical equipment. The probability of exceeding the max pressure of the equipment is; Pr(P t  > p ma x )

(11)

The same equations 8 - 10 will apply for equipment that is not placed on top of the well. The only difference will be the value of the hight,  h . The probability calculation in these cases, will be more complicated.

Reservoir properties

Table 2: Data Value

SI value  

Permeability, k    1000 mD    1E-12 m 2 Oil viscosity, µo  0.5 c p    5E-4 N s /m 2 Oil formation volume factor, µo  1.4 m 3 /Sm 3 1.4 m 3 /Sm 3  Well bore radius, r w  7 i n    0.1764 m  External drainage radius, r e    3000 f t    914.4 m  3 Separator flow rate capacity, q ma x    1000 Sm  /d    1.1547E-3 Sm 3 /s  Formation thickness, h  100 f t    30.48 m 

Table 3: Probability data Reservoir pressure, mean value Reservoir pressure, standard deviation Bottom hole pressure, mean value Bottom hole pressure, standard deviation

300 bar  1 bar  299 bar  0.5 bar 

2.1 Example; probability of exceeding the separators capacity  To illustrate the quantitative approach , an example of the probability of exceeding the separator capacity during an UBD operation is given. Data presented in table 2 and table 3, are normal reservoirs values in the North-Sea. The separators flow rate capacity value, is assumed.

Table 4: Calculations Drawdown, mean value Drawdown, standard deviation Productivity index, J o    Maximum drawdown, ∆p ma x  Probability of exceeding the separator capacity

1 bar  1.12 bar  3.506E-3 m / sbar  3.3 bar  0.02

3 Conclusion and further work  Recommendations to further work on the quantitative approach of blowout frequencies during  UBD and MPD operations, are to; 1. gather uncertainty data. 2. include multiphase flow in the model. 3. develop blowout probabilities for fluid pressure. 4. develop a blowout model for UBD and MPD operations.

References [1] H. A. Asheim. Brønnproduktivitet – http://www.ipt.ntnu.no/ãsheim/info.html , 29.05.2007.

strømning

i

produksjonsrøyr.

Preparatory study

Master Thesis

Risk Assessment of Underbalanced and Managed Pressure Drilling Operations

Preface This report was carried out as a preparation plan for the Master thesis the final year of the Master degree program at NTNU (Norwegian University of Science and Technology). The study was a required task, made to support the work methodology during the projects development. The projects title is; “Risk Assessment of Underbalanced and Managed Pressure Drilling Operations” and was carried out in co-operation with NTNU and Scandpower. Prime and secondary teaching supervisor Marvin Rausand, NTNU, and Alexander Solberg, Scandpower, will be available during the period this project is ongoing.

Table of contents 1

Introduction ........................................................................................................................4 1.1 Background ................................................................................................................ 4 1.2 Main Goal................................................................................................................... 4 1.3 Approach ....................................................................................................................4 1.4 Success criteria........................................................................................................... 4 2 Project planning and control .............................................................................................. 5 2.1 Activity plan – Work Breakdown Structure............................................................... 5 2.2 Work Load.................................................................................................................. 5 2.3 Work Task Analysis................................................................................................... 5 2.4 Project plan – Gantt diagram...................................................................................... 5 Appendix 1 Appendix 2 Appendix 3

Work Breakdown Structure.................................................................................i Work Task Analysis........................................................................................... ii Gantt diagram.................................................................................................... xi

1

Introduction

During the 5th year of master study at NTNU, a Master Thesis will be carried out. In the following report a plan on how the project will be performed is presented.

1.1 Background In recent years, underbalanced drilling (UBD) and managed pressure drilling (MPD) have  been developed as alternatives to the traditional overbalanced drilling technique. The techniques have many advantages compared to overbalanced drilling, but the blowout risk during these operations has not fully been understood

1.2 Main Goal The main object of this thesis is to establish a risk evaluation model for UBD and MPD operations compatible with BlowFAM.

1.3 Approach In order to achieve the main goal there will be performed literature studies on UBD and MPD in conformity with incident investigation during these operations. In order to create a generic  blowout frequency model compatible with BlowFAM, it is necessary to understand how the  program is operates, and the way it works. Because of the scope, not all variants of UBD and MPD operations will be covered in this thesis.

1.4 Success criteria Success criteria related to the project is based on my understanding of technical systems, analytical abilities, and the availability of data and relevant literature.

2

Project planning and control 2.1 Activity plan – Work Breakdown Structure

Work Breakdown Structure, WBS, gives a segmentation of the different work tasks involved in the project and explains how the project is built up. Appendix 1 contains WBS for this  project.

2.2 Work Load The duration of this project is 20 weeks with an estimated consumption of 37, 5 hour each week. According to this the total amount of workload will be 750 hours. A preparatory plan is not a final statement. The project actual performance may vary some from the plan.

2.3 Work Task Analysis Appendix 2 gives a work task description of the activities in WBS.

2.4 Project plan – Gantt diagram A Gantt diagram is a useful tool in order to plan resources and distribute the time available and purposed each project task. The diagram is presented in appendix 3.

 Ap pendi x 1

Work Breakdown Structure

Figure 1 WBS diagram

i

 Ap p end i x 2

Work Wor k Task Anal A nal y si s

 Note that in this section the literature study, activity 3, also is included included in the duration of activities number 4, 5, 6, 7 and 8. Activity 1 Preparatory Study Problem: Perform a preparatory study of the project in order to analyse problems and give a description of work that has to be done in order to produce a good result. The study will contain the project tasks and when they are due in time. Purpose: Create an overview of the workload Define each activities goals Distribute each activities time consume and the amount of work that needs to be done Create a plan for further following-up Content: Preparatory Study with problems to be addressed, goals and demarcations Literature: Rolstadås, A, Praktisk Prosjektstyring, 2001 Various literature Method of work: Create a plan on how the project will be completed Give a problem description Create WBS, CTR and Gantt-diagram Challenges: • • • •

• •

• • •

Activity 2 Progress Report Problem: Prepare a report considering the projects progress, time consumes and modifications compared with the preparation plan. Purpose: View the projects progress, consider derogations and prepare corrections Content: Status report; gives an overview of the projects progress. The report will also show variances that might have occurred regarding the paper and  project goals.|| Literature: Rolstadås, A, Praktisk Prosjektstyring, 2001 Various literature Method of work: Compare the preparation report with the projects actual progress Challenges: Create good solutions as for how to solve possible derogations. Result: A report considering the projects progress along with possible derogations compared to the preparation plan. If derogation, these will be explained, and correction plans will be stated. Duration: •

• •

• •

•

•

•

Hours 7,5

Start 16.03.07

Finish 16.03.07

Activity 3 Literature Study Problem: Gather and seek literature for use in the project Purpose: Find and present relevant literature Content: Gather information from different sources. The literature should be of high quality and create a good foundation in the project. Literature: •

•

Method of work: Seek information from Internet Seek information on BIBSYS Communicate with competent persons Technical and Scientific literature Gather information from reports Challenges: Gather the literature of high quality Sort and select relevant and good literature Result: Create a technical and professional basis for the project Duration • • • • •

• •

•

Hours 352,5

Start 15.01.07

Finish 11.05.07

Activity 4 Describe UBD and MPD Problem: Learn and describe, on a theoretical level, technology and procedures that are used for UBD and MPD. Purpose: Look at different methods and technologies used in offshore industry Get provided with information on how things work and how they are performed Content: Description of UBD and MPD technology and procedures Literature: Research papers Various literature regarding the subject Persons with competence Method of work: Read relevant literature and meet with competent experts. Get an overview of the technology and different methods and equipment that is need. Get familiar with UBD and MPD procedures Challenges: Understand the various technologies and technical terms Get an overview of the different UBD and MPD operations Find relevant literature Results: An overview of different methods and technologies that exist on UBD and MPD. Describe procedures during these operations Duration: • •

•

• • •

• • •

• • •

• •

Activity 5 Hazardous events during UBD and MPD Problem: Identify and describe hazardous events during various steps of a UBD and MPD operation. Purpose: To create a risk picture of UBD and MPD operations. Establish hazardous events Content: Hazard identification by use of an analytical tool Literature: Various literature on risk analysis method Communication with experts Available field performance data Method of work: Choose an analytical method suitable for hazard identification Perform a hazard identification and description by using the analytical tool, interview relevant persons, and analyse available field performance data Challenges: Evaluate which method that is best suited Perform a good hazard identification Results: Identification and description of hazardous events during UBD and MPD operations Create a basis for activity 8 Duration: • •

•

• • •

• •

• •

• •

Hours 187,5

Start 12.02.07

Finish 15.03.07

Activity 6 Description of relevant well control incidents Problem: Investigate different well control incidents related to UBD and MPD operations, and describe the root-causes and causal distributions Purpose: Get a better risk picture of UBD and MPD operations and establish which events that are most risk contributing. Content: Incidents during UBD and MPD operations Root-causes and causal distributions related to these incidents Outline the most important risk contributors Literature: Various literature Incident documentations Communicate with experts and competent persons Method of work: Range different incidents according to size and consequences Identify root causes and causal distributions Establish the most important risk contributors Challenges: The scope of the analysis Find data Find relevant incidents and arrange them into different groups Create a realistic risk picture in UBD and MPD operations Result: What causes well control incidents during UBD and MPD • • •

• • •

• • •

• • • •

Activity 7 Establish formulas between causes and formation characteristics Problem: Establish formulas for relations between the causes of well control incident, in activity 6, and formation characteristics. Purpose: Create a plant specific risk picture of UBD and MPD operations Content: Formulas reflection relations between incident causes, in activity 6, and formation characteristics Literature: Various literature Competent persons Method of work: Look at relation between consequences of well control incidents related to the formation characteristics Use a regression program to create a formula reflecting these relations Challenges: Get enough data Results: Formula reflecting relations between causes of well control incidents and formation characteristics Duration: •

• •

•

•

•

•

Hours 75

Start 16.04.07

Finish 27.04.07

Activity 8 Establish generic blowout frequency models compatible with BlowFAM Problem: Create a blowout frequency model for UBD and MPD which is compatible with BlowFAM Purpose: Further development of BlowFAM in order to include UBD and MPD operations Content: Blowout frequencies during UBD and MPD operations Question list in order to identify plant specific performance Weighting of different plant specific aspects Literature: BlowFAM Various literature Literature from activity 5,6 and 7 Competent persons Method of work: Learn how BlowFAM operates Use results from activity 5, 6 and 7 Create question lists and weight different outcome Challenges: Establish the right questions and give each the right weight Results: Blowout frequency model for UBD and MPD operations in BlowFAM Duration: • • •

• • • •

• • •

•

•

Hours 187,5

Start 30.04.07

Finish 01.06.07

Activity 9 Collocation and printing of project thesis Problem: Complete and hand in the project thesis and make sure the report is consistent Purpose: Make sure the report is consistent, and it is well written Content: Collocation of the report Print and hand in the project Literature: • •

Method of work: Examine the report and make sure it is consistent and grammatically correct. Challenges: Make sure there is none mistakes or defects in the report Results: Hand in a well written report within the time limit. Duration: •

•

•

Hours 37,5

Start 04.06.07

Finish 11.06.07

 Ap pendix 3

Gant t d iagram

Figure 2 Gantt diagram

xi

Progress Report Master Thesis

Risk Assessment of Underbalanced and Managed Pressure Drilling Operations

Progress According to the preparation study report the following activities should have been completed; Activity 1; Preparation study Activity 2; Progress report Activity 4; Describe UBD and MPD Activity 5; Hazardous events during UBD and MPD Activity 6; Description of relevant well control incidents • • • • •

At the present moment only activity 1, 2 and is finished. According to the preparatory study the progress report should have been carried out 16/03-07, but the activity was not performed until 16/04-07. Activity 4 and 5 is mainly finished, but some final writing still has to be done. The activities progress is shown in Table 1 below. Task name Master Thesis

 

Preparatory study Preparatory studty hand in Progress report Progress report hand in Literature study Report writing and analysis Final Report commissioning Final report hand in

Duration [hrs] 750,0 22,5 0,0 7,5 0,0 352,5 330,0 37,5 0,0

% Work Planned Completed 65 100 100 100 100 68 55 0 0

Planned Work % Work  Actual Work Progress [hrs] Completed Progress [hrs] 490,3 62 464,1 22,5 100 22,5 0,0 100 0,0 7,5 100 7,5 0,0 100 0,0 239,7 55 193,9 181,5 40 132,0 0,0 0 0,0 0,0 0 0,0

Table 1 Work progress (19/04-07)

As you cans see from Table 1 the progress has not been as good as planned, but instead of making a new plan I will stick to the original one and try to catch up the undone work.

Deviation