hole cleaning deviated well
TRANSCRIPT
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Hole Cleaning in Deviated Wells
Terry Hemphill
Halliburton Energy Services - Houston
Baroid Drilling Fluids psl
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Signs of Inadequate Hole Cleaning
• Widely-fluctuating rotating torque
• Tight hole and / or pack-offs
• Increased drag after connections
• Rapid increase in ECD when DP rotation initiated
• Problems maintaining angle when sliding
• Stuck pipe [worst case]
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Hole Cleaning in Deviated Wellbore:
The Scenario
Drill Pipe
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Main Topics of Discussion
• Fluid rheological modeling
• Effects of temperature and pressure
• Key parameters affecting hole cleaning
• Cleaning aids• Best practices
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Major Rheological Models in Use
• 2 parameter models
– Bingham plastic
– Power law
– Casson
– Not very accurate across shear rate range
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Major Rheological Models in Use
• 3-parameter models
– Robertson-Stiff
– Herschel-Bulkley
• increased accuracy
• evolving industry standard
• API 13D rewrite in progress
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Downhole Rheological Modeling
• Effect of temperature and pressure most
pronounced on OBM / SBM
• Cold temperature and HPHT rheology
considerations for WBM
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Effects of Temperature and Pressure
on SBM Fluids
• Increasing temperature reduces SBM rheology &density - usually non-linear profile
• Pressure increases SBM fluid rheology & density- fairly linear profile
• Effect of T, P on downhole rheology & densitydependent upon degree of T, P – Computer models
– Fann 70 / 75 data [for fluid rheology]
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SBM Flat Rheology for Deepwater
Drilling
0
10
20
30
40
3900 5748 10600 14700 21000
Depth [ft]
T a u Z e r o [
l b f / 1 0 0 s q f
t ]
DeepWater Fluid
Comp1 Blend
Comp 2 IO
Testing by Third Party Lab
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SBM Flat Rheology for Deepwater
Drilling
0
10
20
30
40
3900 5748 10600 14700 21000
Depth [ft]
T a u Z e r o [
l b f / 1 0 0 s q f
t ]
DeepWater Fluid
Comp1 Blend
Comp 2 IO
Testing by Third Party Lab
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Key Parameters in Hole Cleaning
Modeling - Hole Angle
• Vertical / near-vertical wellbores
[angles < 35 deg deviation]
• Deviated wellbores
[angles > 35 deg deviation]
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Key Parameters in Hole Cleaning
Modeling - Vertical Wells
• Fluid rheological properties
• Pump output
• Hole and pipe geometry
• Mud density• Particle size and shape
• Rate of penetration [ROP]
K P t i H l Cl i
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Key Parameters in Hole Cleaning
Modeling - Deviated Wells
• Fluid rheologicalproperties
• Pump output• Hole and pipe
geometry
• Mud density• Particle size and
shape
• ROP
• Hole angle
• Drill pipe
eccentricity• Drill pipe rotation
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Drill Pipe Eccentricity
• Significant effect on annular pressure drop
• A skewed drill string can have infinite numberof eccentricities at the same time
• Usually an unmeasured factor, but of great
importance to cleaning• While sliding, equals tool joint stand-off
• While rotating > 25 rpm, DP lifts off-bottom
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DP Eccentricity in Deviated Wellbore
Negative Eccentricity
Positive Eccentricity
e < 0
e > 0
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Effect of Drill Pipe Eccentricity
in Deviated Wellbore
• Rapidly alters velocity distribution throughout the
annulus
• Flow in the annular narrow gap greatly reduced;
flow in the wide gap greatly increased
• Flow distribution largely controlled by fluid flowindex ‘n’
• Flow profiles can be generated in computer
programs
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Flow Visualization in
Concentric and Eccentric Wellbore
Concentric-
Vertical drilling
Eccentric-
Deviated sliding
Eccentric-
Deviated drilling
Note: Above techniques qualitatively depict
fluid flow without drill string rotation.
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DP Rotation Effects on Cleaning
• Mechanically disturbs cuttings beds
• Increases annular pressure drop
• Enhances cleaning, effect dependent upon
– annular velocities
– hole angle
– rpm speed
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Effect of DP Rotation on Cleaning
Data ex-Tulsa University
65 degrees deviation, 0.25-in limestone cuttings
0
100
200
300
400
500
600
700
100 150 200 250 300
Avg. Annular Velocity [ft/min]
C u t t i n g s
R e m a i n i n g
[ l b m
25 rpm
75 rpm
125 rpm
175 rpm
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Effect of ROP at High Angles
• Increased ROP reduces hole cleaningefficiency
• Cuttings accumulation increases ECD
increase
• Increased bed heights when circulation
stopped
At constant pump rate, DP rpm, etc:
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Downhole Hydraulics Calculations
• Downhole fluid rheology and density
• Hole cleaning efficiency downhole
• Presence of cuttings beds / annular area
constriction
• Pressure losses, ECD with fluid property inputchanges
• Monitoring of PWD data with model predictions
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Tools to Improve Hole Cleaning
• Increased pump output – most effective
• Increased mud density
• Changes in fluid rheological properties
• Increased DP rotation
• Drilling fluid sweeps
• Bit / cutter diameter selection
• Increased DP size [for ECD and AV]
• Cuttings bed impellers [CBI]
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Drilling High-Angle Wells
Best Practices
• Ensure high enough flow rate [Q] to give adequateAV in open hole – 150-165 ft/min in 8.5-in
– 180 ft/min in 12.25-in
– 125-140 ft/min in large diameters [expect some holecleaning problems]
• If Q is inadequate, investigate changing DP – 5-in to 5.5-in
– 5-in to 5.875-in [special string]
– 5.5-in to 6.625-in
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Drilling High-Angle Wells
Best Practices
• Avoid backreaming as hole cleaning tool
– Excessive pressures on wellbore wall
– Damage to filter cake on borehole wall
– Wellbore instability issues
– Increases incidents of pack-offs and stuck pipe
– Complicates PWD interpretation
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Drilling High-Angle Wells
Best Practices
• Use of sweeps as hole cleaning tools
– Best hole cleaning tool is flow rate/velocity
– Sweeps are secondary tools, not primary tools
– High viscosity for vertical / near-vertical wells
– High density for high-angle wells
– DP rotation enhances sweep performance
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Drilling High-Angle Wells
Best Practices
• Maintain wellbore stability while drilling
– Adequate mud weight to control pore pressures
– Efficient cleaning of an unstable wellbore nearly
impossible task – keep wellbore stable
– Wellbore stability modeling to determine mud densities vs
hole angle and azimuth
– Drilling long intervals with WBM more difficult than with
OBM/SBM
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Drilling High-Angle Wells
Best Practices
• Minimize or eliminate sliding
– Poor cleaning with no DP rotation
– DP lies against low side of hole
• Drill with rotary steerable assemblies
– Can rotate while building angle, steering
– Enhanced hole cleaning
– DP position less eccentric
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The End
Questions?