Hole Cleaning Deviated Well

8/10/2019 Hole Cleaning Deviated Well

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Hole Cleaning in Deviated Wells

Terry Hemphill

Halliburton Energy Services - Houston

Baroid Drilling Fluids psl



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]



Hole Cleaning in Deviated Wellbore:

The Scenario

Drill Pipe



Main Topics of Discussion

• Fluid rheological modeling

• Effects of temperature and pressure

• Key parameters affecting hole cleaning

• Cleaning aids• Best practices



Major Rheological Models in Use

• 2 parameter models

– Bingham plastic

– Power law

– Casson

– Not very accurate across shear rate range



Major Rheological Models in Use

• 3-parameter models

– Robertson-Stiff

– Herschel-Bulkley

• increased accuracy

• evolving industry standard

• API 13D rewrite in progress



Downhole Rheological Modeling

• Effect of temperature and pressure most

pronounced on OBM / SBM

• Cold temperature and HPHT rheology

considerations for WBM



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]



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



Key Parameters in Hole Cleaning

Modeling - Hole Angle

• Vertical / near-vertical wellbores

[angles < 35 deg deviation]

• Deviated wellbores

[angles > 35 deg deviation]




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




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



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



DP Eccentricity in Deviated Wellbore

Negative Eccentricity

Positive Eccentricity

e < 0

e > 0



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



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.



DP Rotation Effects on Cleaning

• Mechanically disturbs cuttings beds

• Increases annular pressure drop

• Enhances cleaning, effect dependent upon

– annular velocities

– hole angle

– rpm speed



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



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:



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



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]



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




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




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




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




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



The End

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Hole Cleaning Deviated Well

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