3.3 Hole Cleaning

1 7/11/2011 Confidential Information © 2010 M-I SWACO

HOLE CLEANING


•

What Affects Hole Cleaning?

Hole Cleaning

ROP

Cuttings

Hole Angle

Inclined Length

Flow Regime

Annular Velocity

Rheology

Eccentricity

Velocity Profile

Rotation

Mud Weight

Formation


• High Annular Velocities– Adequate rig pumps

– Mud rheology to minimize pressure losses in drill pipe

• Optimize solids control equipment to minimize plastic viscosity which raises pressure

losses

• High Yield Points and low “n” values reduce system pressure losses

– Maximize drill pipe OD

• Decreases drill string pressure losses and maximizes flow rates

• Reduced annular space increases velocity

– Use inhibitive muds to maintain gauge hole

Planning, the Key to Hole Cleaning


• Rotate the drill string – no slide drilling

– Steerable rotating heads

– Titanium drill pipe through short radius sections

• Rotate and circulate hole clean before tripping

– Two to four times “Bottoms Up Time”

• No Back Reaming

– Under cuts build sections

– Builds cuttings bed dunes

• Compare hydraulics “What should be” with PWD “What is”

• for difference indicating bed buildup

Planning, the Key to Hole Cleaning

5 7/11/2011 Confidential Information © 2010 M-I SWACOCONFIDENTIAL INFORMATION © 2009 M-I L.L.C.

Optimum

hole-cleaning

conditions for one

interval may be

inadequate

in another

1

2

34


“Boycott” settling accelerates bed formation, especially

in the build section

Clarified Fluid

Suspension Zone

Sag (Sediment) Bed

Slump


Annular Geometry

Horizontal Wells

Annular Diameter

Small Large

Low AV

Laminar FlowLikely

More BedsFluid ChoiceCritical

High AV

TurbulenceEasy

No Beds

Fluid ChoiceNot as Critical


• Wellbore stability crucial

• Mud weight helps stabilize wellbore

• Collapse tendency increases with angle

Mud Weight

Deviated Wells


0

250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

0 50 100 150 200 250 300 350 400 450

Pre

ssu

re L

oss,

Imp

act

Fo

rce,

& H

yd

rau

lic H

ors

ep

ow

er

Flow rate, gpm

Effect of Flow Rate on Pressure Losses, Impact Force & Hydraulic Horsepower

Drill String & Annular LossesBit Pressure Loss

Hydraulic Impact Force

Hydraulic Horsepower

Maximum Allowable Surface Pressure

Optimized for Hyd. Horsepower

Optimized for Impact Force


•

Measurement - Rotational Viscometer

Torsion Spring

Inner Cylinder

Bearing Shaft

Rotor

Bob

Cup

The Viscometer is designed to

measure the shear stress at various

shear rates.

It also can measure the gel strengths

of the drilling fluid.

1. Fluid fills space between rotor and bob.

2. Rotor is rotated at constant speed (shear rate)

3. This induces torque (shear stress) on the bob.

4. The torsion spring acts as restraining force.

5. The bob is deflected to some degree dependant

on amount of stress exerted on bob.

6. The magnitude of the deflection can be

determined (dial readings)

7. Different shear rates are used to determine to

obtain rheological performance of the mud.


• Plastic Viscosity, centipoise

– PV, cp = Rdg 600 – Rdg 300

• Yield Point, lbs/100 ft2

– YP, lbs/100 ft2 = (Rdg 300 - PV)

– YP, lbs/100 ft2 = 2(Rdg 300) – Rdg 600

• Initial Gel, lbs/100 ft2

– Static Rdg 3 - 10 sec after stirring

• 10 minute Gel, lbs/100 ft2

– Static Rdg 3 - 10 minutes after stirring

Interpretation of VG Readings


Viscosity

V2, ft/sec

V1, ft/sec

V2 - V1

d, ft

orRateShear

StressShearityVis

RateShearainMatoForceStressShear

ftd

VVRateShear

ftlbs

ftlbs

ftft

1

100

100

sec1sec21

sec,

,cos

int,

,

,sec,

2

2

Fluid Layer #2

Fluid Layer #1


• Shear Rate = 1.703 X VG rpm

• Shear Stress = 1.0678 X VG rdg

• Metric conversion factor = 478.9

• Therefore:

Viscosity, cp

, ..

.

:

cpVG

VG

or

VG

rdg

rpm

rpm

478 910678

1703

,cp = 300.28VGrdg


• Rdg600 = 50

– Viscosity = 300(50/600) = 25 cp

• Rdg300 = 30

– Viscosity = 300(30/300) = 30 cp

• Rdg100 = 13

– Viscosity = 300(13/100) = 39 cp

• Rdg3 = 5

– Viscosity = 300(5/3) = 500 cp

Viscosity from VG Rdgs

(Illustration of Shear Thinning)

//net.smith.com/mi/ife/MUD SCHOOL TRAINING/Mudschool/Lectures/Hole Clean High Angle Wells/DTCCleaningGraphs.ppt


Skewed velocity

profiles are not

conducive to

cuttings transport

16 CONFIDENTIAL INFORMATION © 2009 M-I L.L.C. 7/11/2011

The Rules


• RT 1- Of the four hole-cleaning ranges, the intermediate

(30° to 60°) typically is the most troublesome.

• RT 2- The upper and lower limits of each hole-cleaning

range should be considered only as guidelines, since all are

affected by factors which influence bed stability, including

cuttings characteristics, drilling fluid properties, and borehole

roughness.

Inclination


• RT 3- Boycott settling can accelerate bed formation,

particularly in 40° - 50° intervals.

• RT 4- Hole-Cleaning parameters considered optimum for

one interval may be inadequate in another interval in the same

well.

• RT 5- Cuttings accumulate in intervals of decreased annular

velocity and can “avalanche” when circulation stops if the

inclination is less than about 50 to 60°.

Well Bore Geometry


• RT 6- The mud systems considered for highly deviated wells

should be modified versions of those proven effective in vertical

and near-vertical offsets in the area.

• RT 7- Drilling fluids with similar rheological properties will

provide comparable hole-cleaning, provided cuttings

characteristics remain constant.

• RT 8- An inhibitive mud helps hole-cleaning in reactive

formations.

Mud Type


• RT 9- Cuttings beds are easy to deposit, difficult to remove.

• RT 10- “Enhanced “ suspensions minimize the formation of

cuttings beds.

Cuttings Beds


• RT 11- The skewed, laminar-flow velocity distribution,

caused by pipe eccentricity and highly non-Newtonian fluids, is not

conducive to cuttings transport.

• RT 12- A highly skewed velocity profile makes it essential to

minimize formation of a cuttings bed on the low side of the hole.

• RT 13- Density stratification in weighted muds aggravates the

skewing of the velocity profile.

Velocity Profile


• RT 14- An increase in annular velocity improves hole cleaning,

regardless of the flow regime.

• RT 15- At high angles, bed height is inversely proportional to

annular velocity.

• RT 16- The cuttings transport mechanism is largely a function of

annular velocity.

Velocity


• RT 17- Laminar flow is preferred if formations are sensitive to

erosion.

• RT 18- Turbulent flow is effective in high-angle, small diameter

intervals in competent formations.

Flow Regime


• RT 19- Hole-cleaning capacity in laminar flow is improved by

elevated low shear-rate viscosity and gel strengths.

• RT 20- It is easier to achieve desired rheological properties in

certain mud systems.

• RT 21- It is easier to maintain proper rheological properties in a

“clean” mud system.

Rheology


• RT 22- Usually, low-velocity, viscous sweeps are ineffective in

high-angle intervals if the pipe is not rotated or reciprocated.

• RT 23- Turbulent sweeps can help hole cleaning if the flow rate

is high and the volume of the sweep is adequate.

Sweeps


• RT 24- Pipe rotation is more effective in viscous muds.

• RT 25- Pipe rotation (and reciprocation) can improve hole

cleaning.

Pipe Rotation


• RT 26- Mud weight increases the buoyant force on the cuttings

and helps hole cleaning.

• RT 27- Weight material can “sag” out of a mud and combine

with the cuttings bed in high-angle intervals.

• RT 28- Hole-cleaning and well bore instability are best

corrected by changing the mud weight.

Mud Weight


• High-to-Intermediate Angles the worst (45-75° most difficult)

• Increased annular velocity improves hole cleaning, regardless of flow

regime

• Elevated low-shear-rate viscosities and gel strengths improve

cleaning

• Drill pipe rotation is key to controlling cuttings beds

Hole Cleaning Summary

Documents

3.3 Hole Cleaning