stuck pipe prevention in high angle wells

Stuck Pipe in High Angle 12¼”HoleCause & Prevention

Peter McNaughton

Baroid Technical Manager - Kuwait

© 2010 Halliburton. All Rights Reserved.

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


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?

� Understand, model, plan!

� The principles are the same for your 12¼” build sections

High angle 17½” & 12¼” intervals

9.5 - 12 ppg OBM


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?

� 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

Relative Clay %

Mixed Layer - Illite + Smectite Illite + Mica Total Reactive Clays, %

Field &

Location

Ahmadi

NE

Magwa

NW

Burgan

S

Ahmadi

NE

Magwa

NW

Burgan

S

Ahmadi

NE

Magwa

NW

Burgan

S

Ahmadi Fm. 14 34 48

Wara Fm. 9 8 4 11 14 7 20 22 11

Mauddud Fm. - 0 - - 73 - - 73 -

Burgan Fm. 16 10 8 18 28 11 34 38 19

Reactive Shale Data – Greater Burgan Area


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)


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, +

� Directional tectonic stress factor,

e.g. 0 – 2.5 ppg, +

� Formation strength factor

e.g. 0 – 1 ppg

Oriented Borehole

Breakout in direction

of Minimum

Horizontal Stress

(σHmin)

σHminσHmax


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

Hole angle:

� 0 - 30

� 30 - 60

� 60 - 90

Mud weight increase:

� 0 – 0.5 ppg

� 0.5 – 1.0 ppg

� 1.0 – 1.5 ppg

Rule of Thumb - Hole angle versus mud weight

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


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

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?

AD-61Lower well section


Hole Cleaning Indicators

Warning signs: Comments

- Hole angle > 30°

- AV < 120 ft/min

- Low pipe rpm

- Mud wt < 10 ppg

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

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

� Do we have a hole cleaning problem?

� 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?


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

� 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

Cuttings bed is

on the low side

of the hole

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


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

� 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

Good hole cleaning –

angular shapePoor hole cleaning –

rounded shapeGood hole cleaning, but

shale is caving

Good hole cleaning, but

mud weight is too low


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


Pill/Sweep Report

Date

2011

Hole

Size

(in)

Bit

Depth

(m MD)

Tangent

Angle

(º)

Pill

Volume

(bbl)

Pill

Weight

(ppg)Pill Composition &

Key Properties

Results, e.g. Before & After Values:

(% increase cuttings at shakers; cuttings/cavings

size & lithology; pick-up & slack-off weight; etc.)

6 Feb 17½ 1255 0 300 8.8

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.

10

Feb12¼ 1400 10 100 9.5

KCl/Polymer premix +

22 ppb CaCO3 (C) + 22

ppb CaCO3 (M) + 22

ppb CaCO3 (F) + 25 ppb

STEELSEAL + 5 ppb

BAROFIBRE + barite

On standby at start of 12¼” interval.

16

Feb12¼ 2419 37 50 12.1

Active mud with 0.25

ppb BAROLIFT

Pumped hole cleaning sweep before trip.

Cuttings volume increased by ~ 50% when sweep

returned. Some large cuttings/cavings with

rounded edges.

Slack-off wt reduced by 10%.

SWEEP & PILL REPORT FORMOperator: xxxx Well: xxxx

� Mud engineer to report hole cleaning sweeps

� Recommended to monitor hole cleaning effectiveness


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


Fluid Viscosity Profile

� Which rheology model is most accurate for hydraulics calcs?

0

20

40

60

80

0 100 200 300 400 500 600

Shear Rate (rpm)

Vis

com

ete

r D

ial R

eadin

g

Measured Points

Herschel-Bulkley

Power Law

Bingham Plastic

600 rpm = 63

300 rpm = 38

200 rpm = 28

100 rpm = 18

6 rpm = 8

3 rpm = 7Herschel-Bulkleymodel closely fits actual fluid profile

Bingham YP

H-B Yield Stress (Tau zero)


Fluid Viscosity Profile

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

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

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

hole cleaning is critical


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?

� These are minimum values

� Actual circulation time will be until the shakers clean up

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


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



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



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



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


Measured Depth

CuttingsBed Height

Flowrate = 900 gpm

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 in any hole section

� < 3% total cuttings load in annulus


Fair Hole Cleaning – Actual Parameters

AD-61, 12¼” Hole at 10,663 ft, Drill w/RSS, Cutting size = 0.3”

MW = 9.0

PV = 20

YP = 25

6 rpm = 10

Tau0 = 7.0

LSR YP = 4

Q = 500 gpm

Rpm = 100

Angle = 610.3 inch cutting.Cuttings bed present.Hole cleaning fair.Max cuttings conc’n < 10% in the high angle section

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


Poor Hole Cleaning – Actual Parameters


MW = 9.0

PV = 20

YP = 25

6 rpm = 10

Tau0 = 7.0

LSR YP = 4

Q = 500 gpm

Rpm = 100

Angle = 61½ 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


MW = 9.0

PV = 20

YP = 25

6 rpm = 10

Tau0 = 7.0

LSR YP = 4

Q = 500 gpm

Rpm = 100

Angle = 61


Good Hole Cleaning – Optimum Parameters


MW = 9.0

PV = 20

YP = 25

6 rpm = 10

Tau0 = 7.0

LSR YP = 4

Q = 600 gpm

Rpm = 100

Angle = 61


Poor Hole Cleaning – Larger Cuttings

AD-61, 12¼” Hole at 10,663 ft, Drill w/RSS, 100 rpm, Cutting size = 0.5”

MW = 9.0

PV = 20

YP = 25

6 rpm = 10

Tau0 = 7.0

LSR YP = 4

Q = 600 gpm

Rpm = 100

Angle = 61


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

Documents

low angle hole high

hole build sections

hole cleaningc

reactive shale inhibition

hole cleaning modeling

pore pressure penetration

causes of stuck pipe

big diameter high angle