Stuck Pipe Prevention in High Angle wells

Stuck Pipe in High Angle 12¼”Hole Cause & Prevention

Peter McNaughton Baroid Technical Manager - Kuwait

Agenda 1. Introduction & Reason for the Presentation 2. Causes & Prevention of Stuck Pipe in High Angle 12¼” hole a. Mud weight b. Hole cleaning c. Monitoring of hole cleaning indicators d. Tripping, circulating & connection practices 3. Kuwait Example, hole cleaning modeling

© 2010 Halliburton. All Rights Reserved.

Introduction Reason for this presentation: Many examples of stuck pipe / tight hole in 12¼” hole build sections Why? Investigate possible causes. Improve planning & execution of future horizontal wells, e.g. Zubair horizontals & Mauddud/Burgan multilaterals Prevent stuck pipe = save drilling days & increase production Introduce the “Two Hat” policy, i.e. different thinking & procedures for: Low angle hole High angle hole


How To Drill Big Diameter High Angle Hole? High angle 17½” & 12¼” intervals 9.5 - 12 ppg OBM

Understand, model, plan! The principles are the same for your 12¼” build sections


Causes of Stuck Pipe in Deviated 12¼” Hole 1. Geology: shale swelling/inhibition & weak formations 2. Borehole instability due to inadequate mud weight 3. Poor hole cleaning practices


Understand the Problem Where Do All the Cavings Come From? What causes all the cavings in the 12¼” build section? Inadequate chemical inhibition? Insufficient hydrostatic head after downhole losses? Roof collapse? Directional tectonic stress? Mechanical disturbance of weak formations? Borehole flexing due to surge/swab pressures? Pore pressure penetration? Time? Combination of these?


Reactive Shale Inhibition Do we have reactive shales in the 12¼” build section? Reactive Shale Data – Greater Burgan Area

Field & Location Ahmadi Fm. Wara Fm. Mauddud Fm. Burgan Fm.

Mixed Layer - Illite + Smectite Ahmadi Magwa Burgan NE NW S 14 9 8 4 0 16 10 8

Relative Clay % Illite + Mica Ahmadi Magwa Burgan NE NW S 34 11 14 7 73 18 28 11

Total Reactive Clays, % Ahmadi Magwa Burgan NE NW S 48 20 22 11 73 34 38 19

Slight to moderate reactive shales exist in 4 formations in the 12¼” build section Shale composition typically doesn’t change much over wide areas, so Burgan data is relevant for North Kuwait


Inhibit Shale Swelling – Mud Formulation Is reactive clay swelling a problem in the 12¼” section? Answer: Do MBT values increase rapidly? Is rheology difficult to control due to clay buildup?

How to control reactive clay swelling? WBM or OBM to control the shales? Balanced salinity OBM is best for inhibition, but lost circulation in the Shuaiba is the risk Experience has shown that a KCl-Polymer system with 3 – 6% KCl is appropriate for the 12¼” build section Glycols, asphaltics etc. are also useful in WBM to: Reduce pore pressure penetration Increase open hole exposure time (OHET) © 2010 Halliburton. All Rights Reserved.

What is Pore Pressure Penetration? Overburden Stress (S) = Matrix Stress (σ) + Pore Pressure (P) Filtrate enters shale thru pores (~1µ diameter), bedding planes & micro-fractures This allows fluid pressure to slowly increase in the shale As pore pressure increases, rock strength decreases This is the main reason that shale destabilizes with time Is shale failure in Kuwait time-dependent? If “yes”, add plugging agents to increase shale capillary entry pressure, or use balanced-salinity OBM


Inadequate Mud Weight Is the mud weight high enough to control:

Oriented borehole breakout (directional tectonic stress) Collapse of unsupported roof Excessive pore pressure in shales Swabbing pressure on connections or trips Loss of hydrostatic head when downhole losses occur


How to Calculate Correct Mud Density Correct mud density depends on what? Maximum expected pore pressure + Safety factor (“trip margin”), e.g. 0.5 ppg + Borehole collapse factor for deviated hole, e.g. 0.5 ppg / 30°of hole angle, + Oriented Borehole Breakout in direction of Minimum Horizontal Stress

Directional tectonic stress factor, e.g. 0 – 2.5 ppg, +

(σHmin)

Formation strength factor e.g. 0 – 1 ppg © 2010 Halliburton. All Rights Reserved.

σHmax

σHmin

Trip Margin & Rock Strength Trip Margin Extra hydrostatic pressure is required to allow some swabbing during a trip out of the hole without inducing a well influx (kick) This safety factor allows a safe trip out of the hole, so is called “Trip margin” “Rule of thumb” value for trip margin is 0.5 ppg KOC’s stated trip margin for drilling fluids = 250 psi above the formation pressure At 10,000ft TVD, 250 psi overbalance = 0.5 ppg Rock Strength Extra mud weight is often required in high angle hole to stabilize weak rock, e.g. coal, fractured shale & loose sand


Mud Weight in Deviated Hole Higher mud weight is required to stabilize unsupported rock (the roof) in high angle hole

Rule of Thumb - Hole angle versus mud weight Hole angle:

Mud weight increase:

0 - 30 30 - 60 60 - 90

0 – 0.5 ppg 0.5 – 1.0 ppg 1.0 – 1.5 ppg


Oriented Borehole Breakout Green log plot shows significant hole enlargement in one direction, but not in another Log for the three caliper arms do not overlap, indicating oval hole shape Circle shapes show oval hole shape in an approximate NNW direction. This is the direction of minimum horizontal stress (σHmin) This agrees with the known tectonic stress regime in Kuwait, where the direction of maximum tectonic stress (σHmax) is at an azimuth of 010°– 045°. Oriented breakout is greatest in the shale (high Gamma Ray values), which is the most stressed lithology.

AH-178 - 12¼” Deviated Hole 4100 – 4300 ft


Casing Depth

AD-61 Lower well section

Is the casing depth optimized to allow the correct MW to be used? Three big problems in the 12¼” build section: Increase MW to control shale pore pressure Increase MW to manage hole angle & tectonic stress Reduce MW due to lost circulation in the Shuaiba

Experience in previous 12-1/4” sections building to high angle shows many hole problems, with stuck pipe common Very difficult to reconcile two opposing mud weight constraints Can we change the casing design?


Hole Cleaning Indicators Do we have a hole cleaning problem? Warning signs:

Comments

- Hole angle > 30°

If one or two of these factors are present, then poor hole cleaning is likely.

- AV < 120 ft/min - Low pipe rpm - Mud wt < 10 ppg

If more than two of these factors are present, then poor hole cleaning is certain to occur.

In Zubair horizontals, two or three of these factors will be present in the 12¼” build section


Inadequate Hole Cleaning

Cuttings bed buildup on the low side of the hole Inadequate annular velocity Drill pipe size versus hole diameter Insufficient drill string rpm Sliding versus rotating Insufficient hole cleaning cycles Inappropriate mud rheology & rheology specifications Incorrect sweeps & sweeps wrongly applied Hole enlargement Cavings Operator & Contractor lack of awareness


Cuttings Beds

Big cuttings (or cavings) rapidly fall to the bottom of the hole Settled cuttings form a “cuttings bed” Cuttings beds restrict hole diameter & cause stuck pipe Cuttings beds can suddenly break free, causing annulus pack-off

Flowrate = 900 gpm

Cuttings Bed on low side of hole


High Angle Hole Cleaning: 7 Primary Factors Hole cleaning factors for deviation > 40°(in order of importance) 1. Annular velocity. Minimum 120 ft/min. AV depends on: Annulus diameter. Big hole diameter = bad; Small pipe diameter = bad. Pump output . More = good Hole enlargement = Bad

2. Cuttings (or cavings) size

Cavings = bad

Big cuttings & cavings cannot be cleaned from a high angle hole

3. Drill string RPM.

High rpm = good. Sliding = bad.

High rpm kicks cuttings from the low side of the hole up into the main flow path

4. Hole angle.

More = bad

Cuttings beds form on the low side of the hole at angles > 40°

5. Mud density

More = good (increased buoyancy)

Hole cleaning problems do not occur at high mud density

6. Hole rheology

Not too thick & not too thin

YP & Funnel Vis are useless values at hole angles > 40°

7. Hole cleaning cycles

How many bottoms up is needed to clean the hole? © 2010 Halliburton. All Rights Reserved.

Annular Velocity Target > 120 ft/min How can we achieve this target through the entire 12¼” build section: Use larger diameter drillpipe → smaller annular diameter in the high angle section Minimize hole enlargement, e.g. Prevent borehole breakout by using the correct mud weight Don’t back-ream

Minimize ultra-fine low gravity solids content, e.g. Improve hole cleaning to remove cuttings quickly Use efficient fine shaker screens, mud cleaners & centrifuges to remove solids on the first pass Maintain a tight LGS specification in the mud


Minimum Flow Rate for AV = 120 ft/min

Hole Size

Annular Velocity (ft/min)

Target Flow Rate, Q (gal/min) 5” drillpipe

5½” drillpipe

6⅝” drillpipe

16”

120

1130

1104

1038

12¼”

120

612

586

519

8½”

120

231

206

-

Gauge Hole

Washed Out Hole


Cuttings Size How big is a cutting from a 12¼” PDC bit (16 mm cutters)? The mud must be able to remove this cutting from the hole


Hole Cleaning – Pipe Rotation Mud flow stream is on the high side of the hole

Rotation disturbs the cuttings bed & kicks cuttings from the low side up into the flow stream

Cuttings bed is on the low side of the hole

Zero hole cleaning when sliding in high angle hole High speed rotation provides: Mechanical disturbance of the cuttings bed, kicking cuttings up into the flow stream “Viscous coupling” of cuttings to the mud film attached to the rotating pipe © 2010 Halliburton. All Rights Reserved.

Hole Cleaning Monitoring How do we measure hole cleaning efficiency? On-bottom & off-bottom torque (do we measure & graph?) Pick-up & slack-off weight on connections (drag) Quantity, size & shape of cuttings at the shakers

Good hole cleaning – angular shape

Poor hole cleaning – rounded shape

Good hole cleaning, but shale is caving

Good hole cleaning, but mud weight is too low

Increased cuttings size & quantity when a sweep returns Tight hole on trips Pump pressure spikes – indicates annulus pack-off Use PWD tool to monitor ECD caused by cuttings load Compare ROP against cuttings at the shaker Waves of cuttings at the shakers © 2010 Halliburton. All Rights Reserved.

Torque & Drag Plot - 12¼” Deviated Hole

Diverging pick-up & slack-off weights indicates a cuttings bed build-up Pick-up & slack-off weights returned to normal after a hole cleaning cycle © 2010 Halliburton. All Rights Reserved.

Pill/Sweep Report Mud engineer to report hole cleaning sweeps Recommended to monitor hole cleaning effectiveness SWEEP & PILL REPORT FORM Operator: xxxx

Date 2011

6 Feb

Hole Size (in) 17½

Bit Depth (m MD) 1255

Tangent Angle (º) 0

Well: xxxx

Pill Volume (bbl) 300

Pill Weight (ppg)

8.8

10 Feb

12¼

1400

10

100

9.5

16 Feb

12¼

2419

37

50

12.1

Pill Composition & Key Properties

Results, e.g. Before & After Values: (% increase cuttings at shakers; cuttings/cavings size & lithology; pick-up & slack-off weight; etc.)

2.5 ppb CMC EHV + 20 ppb Bentonite. Vis = 90 sec/qt.

While POOH at section TD, spotted 300 hi-vis mud to bottom. No drag or overpull while POOH.

KCl/Polymer premix + 22 ppb CaCO3 (C) + 22 ppb CaCO3 (M) + 22 On standby at start of 12¼” interval. ppb CaCO3 (F) + 25 ppb STEELSEAL + 5 ppb BAROFIBRE + barite Pumped hole cleaning sweep before trip. Cuttings volume increased by ~ 50% when sweep Active mud with 0.25 returned. Some large cuttings/cavings with ppb BAROLIFT rounded edges. Slack-off wt reduced by 10%.


Hole Cleaning – Optimum Rheology What is the optimum mud rheology in high angle hole? “Not too thin” Thin mud cannot suspend big cuttings (or cavings) They rapidly fall to the bottom of the hole to form a “cuttings bed”

“Not too thick” Thick mud cannot penetrate the cuttings bed under the drill pipe Thick mud will travel up the high side of the hole

“Just right” Intermediate rheology is best Rule of thumb: 6 rpm viscometer value ≈ 0.8 – 1.5 x hole diameter (inches) For big hole, use 1.2 – 1.5 x hole diameter For small hole, use 0.8 – 1.0 x hole diameter


High Angle Hole – Rheology Specification Best rheology specification for high angle hole? 6 rpm Viscometer Dial Reading

Closest measurement to the annulus flow rate past the drillpipe Closest measurement to the most difficult annulus section to clean

Low Shear Rate Yield Point (LSR YP)

Calculates YP using 3 & 6 rpm viscometer values LSR YP = 2 x θ3 – θ6 Represents the annulus flow rate past the drillpipe better than Bingham YP Sometimes inaccurate. Small differences in viscometer values can cause big changes in LSR YP.

Herschel-Bulkley Tau Zero (Yield Stress)

Intercept on Y-axis of viscometer dial reading versus viscometer speed “True Yield Point” Calculated by curve fit to actual mud viscosity profile Gives more accurate hydraulics calculations than Bingham or Power Law © 2010 Halliburton. All Rights Reserved.

Fluid Viscosity Profile Which rheology model is most accurate for hydraulics calcs?

Viscometer Dial Reading

80 Measured Points Herschel-Bulkley

60

Power Law Bingham Plastic 600 rpm = 63 300 rpm = 38 200 rpm = 28 100 rpm = 18 6 rpm = 8 3 rpm = 7

40 Bingham YP

20 Herschel-Bulkley model closely fits actual fluid profile

0 H-B Yield Stress (Tau zero)

0

100

200

300

400

Shear Rate (rpm)


500

600

Fluid Viscosity Profile

6 rpm viscometer reading is the best measure of the fluid viscosity in the open hole annulus where hole cleaning is critical

For 12 ¼” hole & 120 ft/min annulus velocity : Annulus shear rate = 2.4 x AV / [Dh – Dp] = 40 sec-1 Equivalent viscometer rotor speed = annulus shear rate / 1.703 = 23 rpm

120ft/min annular velocity in 12-1/4” hole


Baroid Recommended Rheology Spec Recommended rheology spec. for deviated hole Use Yield Point for hole angle < 40° Use 6 rpm viscometer value for hole angle ≥ 40° Recommend rheology range for 12¼” high angle hole 6 rpm viscometer value = 12 – 16 (for MW < 10 ppg) 6 rpm viscometer value = 10 – 14 (for MW > 10 ppg)


Hole Cleaning Cycle 1. How many bottoms up (cycles) to clean the hole? 2. What is the Circulation Factor? Deviation

Circulation Factor (= minimum circulation volume) Hole Size 17½” & 16” 12¼” 8½” Vertical (<10°) 1.5 x B/U 1.3 x B/U 1.3 x B/U 10 - 30° 1.7 x B/U 1.4 x B/U 1.4 x B/U 30 - 60° 2.5 x B/U 1.8 x B/U 1.6 x B/U > 60° 3.0 x B/U 2.0 x B/U 1.7 x B/U

These are minimum values Actual circulation time will be until the shakers clean up


High Angle Hole Cleaning – Secondary Factors Hole Cleaning Sweeps 1. Good Sweeps: Best sweep materials are: Weighted sweeps Provide buoyancy. Best if 4 ppg > MW. Coarse fibres. Fibres form a mat; Sweep is removed by shakers Coarse Barite weighted sweep (Sweep-Wate) Sweep is removed by shakers Keep sweep rheology the same as mud rheology.

2. Bad Sweeps Hi-vis sweeps are useless in high angle hole Sweep goes up the high side of the hole Cuttings bed remains on the low side of the hole Tandem sweeps cause more harm than good: Low-weight component may rise in the well & cause a kick Low-weight component can cause borehole wall to flex & weaken Hi-vis component is useless in high angle hole Tandem sweeps destabilize mud properties © 2010 Halliburton. All Rights Reserved.

High Angle Hole Cleaning – Secondary Factors Circulating Practices Circulate cuttings above the BHA before making a connection Circulate at drilling flow rate & rpm when reaming upwards Circulate at drilling flow rate & low rpm when reaming downwards (to avoid inadvertently kicking off into new hole) Circulate the correct number of bottoms-up cycles, based on:

Circulation factor Drillstring rpm Hole angle Possible hole enlargement

Circulate until the shakers clean up Circulate sweeps all the way out (do not stop pumping) Do not have more than one sweep in the hole at the same time DO NOT BACKREAM unless it is the only way to get out of the hole


High Angle Hole Cleaning – Secondary Factors The trouble with back-reaming: Pipe is pulled into the roof of the hole when back-reaming Large cuttings are cut from the roof of the hole This causes several problems:

Hole diameter gets bigger, so annulus velocity reduces Extra large cuttings are generated that must be removed from the hole The extra large cuttings may block the annulus (annulus pack-off) Stuck pipe often occurs when back-reaming, usually after a pack-off occurs


High Angle Hole Cleaning – Secondary Factors Tripping Practices A cuttings bed will always be present in 12¼” hole at angles > 40° You will drag cuttings up the hole when you trip (snowplow effect) If tight hole occurs on the trip out:

DO NOT BACKREAM RIH one or two stands Perform a hole cleaning cycle (high rpm & flow rate) POH again If the tight spot is not there, then it was caused by a cuttings bed


Drillstring Failure & Corrosion Monitoring

High angle big diameter hole puts maximum stress on the drill string Weakness caused by corrosion will cause the drillstring to fail Stuck pipe in high angle hole is expensive (expensive tools are lost) Stuck pipe in high angle hole is difficult to fish

To prevent drillstring failure in high angle drilling: Use corrosion monitoring & treatment to reduce the risk of failure Blueprint, register & inspect all pipe, crossovers & subs run in the hole Use lubricants (including OBM lubricants) to reduce torque & drag Minimize cumulative dogleg in the upper hole to reduce torque & drag


Case History – North Kuwait AD-61 Abdaly Field, North Kuwait Horizontal Zubair producer 12¼” interval with 5” DP Build hole angle to 67° Water base mud (KCl-Polymer- Glycol) Drill with rotary steerable system (RSS) or mud motor Twisted off while reaming tight hole at 10,750 ft. Unable to fish Inadequate hole cleaning partly to blame Similar occurrences in AD-57, including stuck pipe, annulus pack-off & tight hole requiring backreaming


Hole Cleaning in High Angle Wells Baroid’s DFG Hole Cleaning Modeling

Calculate cuttings loading in annulus Identifies poor hole cleaning Calculates ECD of mud system & sweeps Optimize rheology & other hole cleaning factors Can be used in real time with PWD tool

Hole Cleaning – Rules of Thumb < 10% cuttings load inMeasured any holeDepth section < 3% total cuttings load in annulus

Cuttings Bed Height


Flowrate = 900 gpm

Fair Hole Cleaning – Actual Parameters

0.3 inch cutting. Cuttings bed present. Hole cleaning fair. Max cuttings conc’n < 10% in the high angle section

MW = 9.0 PV = 20 YP = 25 6 rpm = 10 Tau0 = 7.0 LSR YP = 4 Q = 500 gpm Rpm = 100 Angle = 61

AD-61, 12¼” Hole at 10,663 ft, Drill w/RSS, Cutting size = 0.3” © 2010 Halliburton. All Rights Reserved.

Hole cleaning OK. Avg. cuttings conc’n < 3.0%

Poor Hole Cleaning – Actual Parameters

½ inch cutting. Large cuttings bed. Hole cleaning poor. Max cuttings conc’n > 10% in the high angle section


Hole cleaning poor. Avg. cuttings conc’n > 3.0%

ECD with cuttings very high


Very Poor Hole Cleaning – Actual Parameters



Good Hole Cleaning – Optimum Parameters



Poor Hole Cleaning – Larger Cuttings


AD-61, 12¼” Hole at 10,663 ft, Drill w/RSS, 100 rpm, Cutting size = 0.5” © 2010 Halliburton. All Rights Reserved.

Summary Understand, model & plan for high angle big hole! Two hats: Low angle & high angle hole are completely different Understand: Geology → correct mud type & inhibition Pressures & forces → correct mud weight Hole cleaning issues → optimize practices → optimize or improve equipment → optimize rheology

For interest, compare our findings with SPE 151953, “Planning & Well Design for KOC’s first North Kuwait Jurassic Well (SA297) – Case History”, 2012


How Did We Drill This Well w/o Stuck Pipe?

Understand, model, plan! Borehole stability analysis Extensive hole cleaning & ECD modeling using DFG Rigsite torque & drag monitoring Optimized rheology Circulate before trips until the hole is clean High weight sweeps (fibres not allowed) OBM lubricant No wiper trips No backreaming, except before running casing

Equipment 4 x 2000HP mud pumps, with 7500 psi fluid ends 7500 psi standpipe 1200 gpm in 17-1/2” hole 800 -900 gpm in 12-1/4” hole PWD tool 5 Derrick 4-panel 514 shakers 2 mud cleaners 3 centrifuges RSS mandatory, rotating at 150 – 180 rpm 5-7/8” drillpipe (later 6-5/8” DP) Non-rotating stabilizers Roller centralizers to run casing 9000 bbl mud system Mud plant at the rig Cuttings slurrification unit, injection pump & injection well at the rig


Stuck Pipe Prevention in High Angle wells

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