14c- multilateral drilling operations and tools power point

1

HORIZONTAL DRILLINGHORIZONTAL DRILLING

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2 © 2007 PetroSkills LLC, All Rights Reserved

EvolutionEvolution

Originally, all Originally, all wells were wells were short radiusshort radiusThen started Then started drilling long drilling long and medium and medium radiusradius

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50

100

150

200

250

1984 1985 1986 1987 1988

Year

Num

ber

of H

oriz

onta

l Wel

ls

Long RadiusMedium RadiusShort Radius


EvolutionEvolution

The The number number of of horizontal horizontal wells wells drilled drilled continues continues to to increase increase with timewith time

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

YEAR

WEL

LS -

WO

RLD

WID

E


BUILD RATESBUILD RATES

UltraUltra--short Radiusshort RadiusShort RadiusShort RadiusIntermediate RadiusIntermediate RadiusMedium RadiusMedium RadiusLong RadiusLong Radius


ULTRAULTRA--SHORT RADIUSSHORT RADIUS

45 to 90 degrees per foot45 to 90 degrees per footUses highly specialized equipmentUses highly specialized equipmentHorizontal lengths of 100Horizontal lengths of 100’’ to 200to 200’’Used primarily in unconsolidated, Used primarily in unconsolidated, heavy oil sandsheavy oil sandsDrills with hydraulics, therefore Drills with hydraulics, therefore formations must be softformations must be softNot used muchNot used much


Ultra Short RadiusUltra Short Radius


Definitions have changed with timeDefinitions have changed with time


Definitions have changed with timeDefinitions have changed with timeLong Radius

Intermediate Radius

Medium Radius

Short Radius

2º – 6º/100 ft3000 – 1000 ft radii914 – 305 m radii




300 to 2000 ft*

200 to 1000 ft+

2000 to 4000 ft*

3000 to 5000 ft*

*Depends Upon Build Rate+Depends Upon Equipment Used

DRILLING TECHNIQUES

1000 to 1500 m

600 to 1200 m

90 to 600 m

60 to 300 m

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SHORT RADIUSSHORT RADIUS

150 to 300 degrees per 100150 to 300 degrees per 100’’ build ratesbuild ratesUses specialized equipmentUses specialized equipmentMechanical and motor systems availableMechanical and motor systems availableTypically used in sidetracking existing wellsTypically used in sidetracking existing wellsBending stress and fatigue can be a problemBending stress and fatigue can be a problem200200’’ to 1000to 1000’’ (60 to 300 m) horizontal section (60 to 300 m) horizontal section lengths depending upon equipment usedlengths depending upon equipment used

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Short RadiusShort Radius

The original short The original short radius system radius system was a mechanical was a mechanical systemsystemThe curved The curved drilling guide was drilling guide was used to drill off a used to drill off a whipstockwhipstock

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The horizontal section was drilled with a The horizontal section was drilled with a flexible rotary bottomhole assemblyflexible rotary bottomhole assemblyInclination was changed by adjusting Inclination was changed by adjusting stabilizersstabilizersCould not control directionCould not control direction



Articulated drill pipe was used through the Articulated drill pipe was used through the build curve and into the horizontal to build curve and into the horizontal to prevent fatigueprevent fatigue



Pushing on the Pushing on the articulated drill articulated drill pipe is similar to pipe is similar to pushing on a pushing on a chainchainHorizontal Horizontal section length section length was usually was usually limited to 200 to limited to 200 to 300 feet (60 to 90 300 feet (60 to 90 m)m)



Short radius Short radius motor system motor system with flexible with flexible motor assemblymotor assemblyThree bends in Three bends in the assemblythe assembly



Motor systems Motor systems were more were more efficient than the efficient than the mechanical mechanical systemssystemsMechanical Mechanical systems are not systems are not used much todayused much today



Even though the Even though the motor systems motor systems are more are more expensive, they expensive, they can result in can result in lower cost per lower cost per foot due to more foot due to more efficient drilling efficient drilling and longer and longer horizontal lengthshorizontal lengths


Short Short RadiusRadius

Baker short Baker short and and intermediate intermediate radius motor radius motor systemssystemsTools Tools change with change with timetime



Another mechanical system Another mechanical system developed by Amoco and deployed developed by Amoco and deployed by by GrandDirectionsGrandDirectionsAll rotaryAll rotary



Curve drilling assembly (CDA)Curve drilling assembly (CDA)Gyroscopic surveying tool to orient the CDAPulled after the curve has been completed



Curve drilling assembly (CDA)Curve drilling assembly (CDA)Builds curve by rotatingComposite or titanium pipe above the CDA to prevent fatigue



Drills the horizontal section with Drills the horizontal section with limited rotationlimited rotationThe 2 3/8The 2 3/8”” tubing is used on only one tubing is used on only one well to minimize fatigue damagewell to minimize fatigue damageThen the tubing is used in vertical Then the tubing is used in vertical wells to complete the wellswells to complete the wells



Dp

Dh

Dh - DpClearance

r

L

Not all Not all tools tools will go will go through through the build the build curve in curve in short short radius radius drillingdrilling


ShortShort RadiusRadius

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5.00

10.00

15.00

20.00

25.00

0 50 100 150 200 250 300

Dogleg Severity, deg/100 feet

Max

imum

Too

l Len

gth,

feet

3"

2"

1"

0.5"

Clearance

Radius of curvature, feet115 57 38 29 23 19573

( ) ( )2242 phph DDDDrL −+−=



Bending stresses and fatigue are a problem in Bending stresses and fatigue are a problem in short radius drillingshort radius drilling

0

20,000

40,000

60,000

80,000

100,000

120,000

20 40 60 80 100 120 140 160

Dogleg Severtiy, deg/100 ft

Ben

ding

Str

ess,

psi

3 1/2" OD2 7/8" OD

σb

= +/-(218)(OD)(DLS)σb

= Bending Stress, psiOD = Pipe outside diameter, inDLS = Dogleg Severity, º/100’



Tubular RequirementsTubular RequirementsGrade 105 and higherPH6 Hydril or SL H90 connectionsID to allow 1.75” tool to pass

HistoryHistoryP110 G105 S1352 7/8” OD 2 7/8” OD 2 7/8” OD8.7 lb/ft 10.4 lb/ft 10.4 lb/ftPH6 Hydril SL H90 SL H90



Sidetrack methodSidetrack methodOpen holeSection millWhipstock



Completion HistoryCompletion HistorySlotted linerZonal isolationSand controlOpen hole


INTERMEDIATE RADIUSINTERMEDIATE RADIUS

25 to 100 degrees per 10025 to 100 degrees per 100’’ build ratesbuild ratesUses specialized equipmentUses specialized equipmentTypically used in sidetracking Typically used in sidetracking existing wellsexisting wellsBending stress and fatigue can be a Bending stress and fatigue can be a problem especially at the higher problem especially at the higher build ratesbuild rates300300’’ to 2000to 2000’’ (90 to 600 m) horizontal (90 to 600 m) horizontal lengths depending upon build rateslengths depending upon build rates



In the build section, the motor cannot In the build section, the motor cannot be rotatedbe rotatedAt the lower end of intermediate At the lower end of intermediate radius, the motor can be rotated radius, the motor can be rotated while drilling the lateral without while drilling the lateral without causing significant fatigue damage causing significant fatigue damage to the drill pipeto the drill pipeSmaller diameter pipe can be rotated Smaller diameter pipe can be rotated at higher build ratesat higher build rates



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25,000

50,000

75,000

100,000

125,000

150,000

175,000

200,000

0 25 50 75 100 125 150 175 200 225 250

Dogleg Severity, deg/100 ft

Ben

ding

Str

ess,

psi

2 7/8" OD3 1/2" OD4 1/2" OD

No Rot at ion Allowed

Limit ed Rot at ion

Rot at ion Allowed



•• In the mid range, the motor can be In the mid range, the motor can be rotated while drilling the lateral, but rotated while drilling the lateral, but rotation must be limitedrotation must be limited• The motor is usually rotated slowly to

reduce the total number of cycles in the build curve

• Some fatigue damage to the pipe does result



•• At the higher end of intermediate At the higher end of intermediate radius, motor rotation should be very radius, motor rotation should be very limited with smaller diameter limited with smaller diameter tubulars onlytubulars only• Since the pipe in the build section is

fatigued, the cost of the pipe is considered as part of the cost of drilling the well

•• When the motor can be rotated in the When the motor can be rotated in the lateral, the amount of lateral that can lateral, the amount of lateral that can be drilled is increasedbe drilled is increased



•• Getting completion equipment into Getting completion equipment into the hole may be a problem at the the hole may be a problem at the higher build rates but is not a higher build rates but is not a problem at the lower build ratesproblem at the lower build rates


MEDIUM RADIUSMEDIUM RADIUS

8 to 25 degrees per 1008 to 25 degrees per 100’’ build ratesbuild ratesUses what is now considered Uses what is now considered conventional equipmentconventional equipmentHorizontal section lengths have been Horizontal section lengths have been drilled over 7000drilled over 7000’’ (2130 m) but (2130 m) but typically 2000typically 2000’’ to 4000to 4000’’ (600 to 1200 (600 to 1200 m)m)No problem with bending stress or No problem with bending stress or completion equipmentcompletion equipment



Build rate depends upon hole size, Build rate depends upon hole size, higher build rates can be used in higher build rates can be used in smaller diameter holessmaller diameter holesTable showing Sperry Sun build Table showing Sperry Sun build rates for medium radiusrates for medium radius

Hole size (in.) Build Rate (°/100ft)

Radius (ft)

6 to 6 3/4

12 to 25

478 to 2298 1/2

10 to 18

573 to 318

12 1/4

8 to 14

716 to 409



Motor rotation is not allowed in the build Motor rotation is not allowed in the build section as it will cause problems with section as it will cause problems with stresses in the motor and the BHA stresses in the motor and the BHA connections except with specific motors connections except with specific motors at the lowest build ratesat the lowest build ratesMotor rotation is allowed in the lateralMotor rotation is allowed in the lateralFatigue is a minimal problem with larger Fatigue is a minimal problem with larger diameter tubulars at the high end of diameter tubulars at the high end of medium radiusmedium radius


Medium RadiusMedium Radius

Medium radius Medium radius uses a uses a conventional conventional motor with a bent motor with a bent housinghousingAt the higher build At the higher build rates, it uses a rates, it uses a double bend motor double bend motor with a bend in the with a bend in the motor and at the motor and at the top of the motortop of the motor



Medium radius Medium radius uses a uses a conventional conventional motor with a bent motor with a bent housinghousingAt the higher build At the higher build rates, it uses a rates, it uses a double bend motor double bend motor with a bend in the with a bend in the motor and at the motor and at the top of the motortop of the motor



Kick pad


LONG RADIUSLONG RADIUS

2 to 6 degrees per 1002 to 6 degrees per 100’’ build ratesbuild ratesUses conventional equipmentUses conventional equipmentHorizontal section lengths have been Horizontal section lengths have been drilled over 20,000drilled over 20,000’’ (6000 m) but (6000 m) but typically 3000typically 3000’’ to 5000to 5000’’ (900 to 1500 (900 to 1500 m)m)No problem with bending stress, No problem with bending stress, fatigue or completion equipmentfatigue or completion equipment


LONG RADIUSLONG RADIUS

Build section is steerable, which Build section is steerable, which means the motor can be rotated in means the motor can be rotated in the build sectionthe build section66oo/100/100’’ is a 955is a 955’’ (291 m) radius(291 m) radiusOffshore uses long radius almost Offshore uses long radius almost exclusively since longer departures exclusively since longer departures are required before the well gets to are required before the well gets to be horizontalbe horizontal


Long RadiusLong Radius


TorqueTorque

The amount of torque and drag will The amount of torque and drag will limit the horizontal section length limit the horizontal section length drilleddrilledTorque in pipe over length Torque in pipe over length ΔΔLL

M2

= M1

+ (μ

FN

r)


DragDrag

The biggest The biggest problem is problem is usually the usually the down drag down drag when pipe when pipe buckling buckling occursoccurs


DragDragHorizontal Section Length vs Hook Load

Build Rate 10 º/100'5.5 inch Pipe, 9.0 ppg

010000200003000040000500006000070000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Horizontal Section Length, feet

Hoo

k L

oad,

lbs

Frict ion Co efficient = 0 .2Frict ion Co efficient = 0 .3Frict ion Co efficient = 0 .4Frict ion Co efficient = 0 .5


CompletionCompletion

Slotted linerSlotted linerScreen or preScreen or pre--packed screenpacked screenGravel packGravel packOpen holeOpen holeCased and cementedCased and cementedSlotted liner and ECPSlotted liner and ECP’’ss


Completion Completion ––

Slotted LinerSlotted Liner


Completion Completion –– Sand ScreenSand Screen

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Slotted Liner and Slotted Liner and ECPECP’’ss



Cement and Cement and PerforatePerforate



Open HoleOpen Hole


RigRig

A large rig is A large rig is not required to not required to drill a horizontal drill a horizontal wellwellHook loads may Hook loads may not be very highnot be very highPumps are the Pumps are the most important most important when selecting when selecting a rig for a a rig for a horizontal wellhorizontal well


Logging High Angle and Horizontal Logging High Angle and Horizontal WellsWells

Generally above 60Generally above 60oo, wireline logs , wireline logs will not go to bottomwill not go to bottomAlternative logging methods are Alternative logging methods are required since the logs must be required since the logs must be physically pushed into the holephysically pushed into the hole

LWD (Logging While Drilling)PCL (Pipe Conveyed Logging)CTC (Coiled Tubing Conveyed Logging)Well Tractor


LWDLWD

LWD tools are an LWD tools are an integral part of the integral part of the drill stringdrill stringLWD tools are added LWD tools are added to the MWD tool and to the MWD tool and the MWD pulser the MWD pulser sends the sends the information to the information to the surfacesurfaceSome of the LWD Some of the LWD data may be stored data may be stored in memory and in memory and downloaded laterdownloaded later


LWDLWD

Typical layout of Typical layout of LWD tools within LWD tools within the directional the directional bottomhole bottomhole assemblyassembly

Neutron

Density

DirectionMeasurements

GR

Resistivity

InclinationGRButton Resistivity

Resistivity at BitFeet from Bit

0 ft

20 ft

40 ft

60 ft

80 ft

100 ft

120 ftNeutron

Density

DirectionMeasurements

GR

Resistivity

InclinationGRButton Resistivity

Resistivity at BitFeet from Bit

0 ft

20 ft

40 ft

60 ft

80 ft

100 ft

120 ft

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Advantages of LWDAdvantages of LWDLogging data is available while drilling to help pinpoint target formations allowing more accurate placement (geosteering)LWD can provide early reservoir evaluation and delineationCasing or core point selection is made easierLWD can provide logs for wells that are difficult to logLWD logs can be used for pore pressure prediction



Disadvantages of LWDDisadvantages of LWDWith more logs, only some of the logging data can be sent to the surface using the mud pulse systemLWD is relatively expensive and rig rates must be higher to offset the costIf the LWD logs are lost in the hole, it can get very expensiveMore logs means that the directional sensors are farther from the bitPossible loss of neutron source in hole



Pipe Conveyed LoggingPipe Conveyed LoggingThe logs are attached to the end of the drill string and tripped into the hole to the point where logging is to begin



Pipe Conveyed Pipe Conveyed LoggingLogging

A side entry sub is installed and the wireline is connected to the logs with a wet connect



Pipe Conveyed Pipe Conveyed LoggingLogging

Logging proceeds by running the pipe to TD and pulling back outThe logs are run by the driller on the drilling rig

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Must be good communication between the logging truck and the drillerIt is important to keep good track of the depth of the wireline and the drill stringDo not want any extra line left in the hole when the side entry sub reaches the rig floorMust take care not to get the wireline caught in the slips or the tongs



Coiled tubing conveyed logging uses Coiled tubing conveyed logging uses a coiled tubing unit with a wireline a coiled tubing unit with a wireline inserted into the coiled tubinginserted into the coiled tubingUsually only done in cased hole due Usually only done in cased hole due to the buckling tendency of coiled to the buckling tendency of coiled tubing in a larger diameter holetubing in a larger diameter holeCan use coiled tubing to run Can use coiled tubing to run production logs, cased hole logs and production logs, cased hole logs and perforating gunsperforating guns



Can also use a well tractorCan also use a well tractorThe logging tool has a mechanism The logging tool has a mechanism for pulling the logs into the holefor pulling the logs into the holeThe power is provided through the The power is provided through the wirelinewirelineUsed mostly in cased holeUsed mostly in cased hole


Hole CleaningHole Cleaning

Hole cleaning in a vertical Hole cleaning in a vertical well is a function ofwell is a function of

Annular velocityParticle diameterMud viscosity, andMud density

( ) 71.0

4.06.0

6.1

6.346⎥⎥⎦

⎤

⎢⎢⎣

⎡ −=

fe

fPps

dV

ρμρρ



If the annular velocity of the drilling If the annular velocity of the drilling fluid exceeds the settling velocity of fluid exceeds the settling velocity of the particle, the particle will be the particle, the particle will be carried out of the holecarried out of the holeIf not, the particle must be ground If not, the particle must be ground smaller until the settling velocity is smaller until the settling velocity is lower than the annular velocitylower than the annular velocityVVpp = = VVff –– VVss



In a directional In a directional well, the particle well, the particle velocity is still a velocity is still a function of the function of the velocity of the fluid velocity of the fluid and settling and settling velocity but they velocity but they are no longer are no longer directly opposingdirectly opposingThe particle will The particle will seek the low side seek the low side of the holeof the hole



A cuttings bed A cuttings bed will form on the will form on the low side of the low side of the hole unless the hole unless the annular velocity annular velocity is high enough to is high enough to erode the erode the cuttings bedcuttings bed

ShakerWellbore

Cuttings

Mud

Cuttings Bed



After a cuttings bed is formed, the After a cuttings bed is formed, the fluid in the annulus will have to erode fluid in the annulus will have to erode the cuttings bed in order to carry the the cuttings bed in order to carry the cuttings up the hole cuttings up the hole The bed will continue to grow The bed will continue to grow narrowing the annular space and narrowing the annular space and causing an increase in the annular causing an increase in the annular velocity until the rate of erosion velocity until the rate of erosion equals the rate of depositionequals the rate of deposition



Experiments were conducted in the Experiments were conducted in the laboratory to determine how mud laboratory to determine how mud viscosity, flow regime and annular viscosity, flow regime and annular velocity affects hole cleaning in a velocity affects hole cleaning in a directional welldirectional wellThree drilling fluids were usedThree drilling fluids were used

The first was water, which has a very low viscosity and is always in turbulent flow



Experiments were conducted in the Experiments were conducted in the laboratory to determine how mud laboratory to determine how mud viscosity, flow regime and annular viscosity, flow regime and annular velocity affects hole cleaning in a velocity affects hole cleaning in a directional welldirectional wellThree drilling fluids were usedThree drilling fluids were used

The first was water, which has a very low viscosity and is always in turbulent flow

ShakerWellbore

Cuttings

Mud

Cuttings Bed



The second fluid was a lightly gelled mud with a low viscosity. The viscosity was low enough so that the fluid was in turbulent flow even at lower annular velocitiesThe third fluid was a higher viscosity mud. Even at high flow rates, laminar flow was maintained



Water PV = 1 YP = 0, always turbulentMud PV = 3 YP = 2, always turbulentMud PV = 19 YP = 17, always laminar

ResultsResults00°° and 10and 10°°

Wells with inclinations between 0° and 10°behave the same as vertical wells



Increasing annular velocity and viscosity will improve hole cleaning

( ) 71.0

4.06.0

6.1

6.346⎥⎥⎦

⎤

⎢⎢⎣

⎡ −=

fe

fPps

dV

ρμρρ



0

10

20

30

40

0 20 40 60 80Inclination, degrees

Cut

tings

Con

cent

rat

Turb. Water 115'/min Turb. Mud 115'/min Lam. Mud 115'/minLam. Mud 172'/min Turb. Mud 229'/min Lam. Mud 229'/min

Laminar Mud PV= 19 YP= 17Turbulent Mud PV= 3 YP= 2Turbulent Water PV= 1 YP= 0



1010°° to 30to 30°°At velocities less than 120 fpm (37 mpm), the cuttings will settle to the low side of the hole and slide down the wellboreWithin a short distance, they will again end up in the higher velocity portions of the annulus and be carried up the hole

ShakerWellbore

Cuttings

Mud



The hole cleaning capacity of the mud at this inclination is not as efficient as vertical wellsAt annular velocities above 120 fpm (37 mpm), the cuttings are not able to form a bed on the low side of the hole, but rather are carried up the wellbore along the low side in slugs or dunes



At flow rates in excess of 180 fpm (55 mpm), the cuttings are carried smoothly along the low side of the hole



0

10

20

30

40


Cut

tings

Con

cent

ratio

n

Turb. Water 115'/min Turb. Mud 115'/min Lam. Mud 115'/min

Lam. Mud 172'/min Turb. Mud 229'/min Lam. Mud 229'/min


At flow rates in excess of 180 fpm (55 mpm), the cuttings are carried smoothly along the low side of the hole



3030°° to 60to 60°°Hole cleaning is the most critical at inclinations between 30° and 60° with the inclinations between 40° and 50° being the most difficult A cuttings bed forms at 40° with an annular velocity less than 150 fpm (45 mpm)At 50°, a bed would form at annular velocities of 180 fpm (55 mpm)



Not only can a cuttings bed form rapidly at these inclinations, but the cuttings slide down the wellbore on the low side of the hole when the pump is turned off

ShakerWellbore

Cuttings

Mud

Cuttings Bed



Not only can a cuttings bed form rapidly at these inclinations, but the cuttings slide down the wellbore on the low side of the hole when the pump is turned off

ShakerWellbore

Cuttings

Mud

Slumped Cuttings Bed



In directional wells with inclinations less than 40°, the cuttings will fall to the bottom of the holePoor hole cleaning will be evidenced by fill on bottom



In high inclination or horizontal wells, the cuttings will fall to a maximum inclinationPoor hole cleaning will be evidenced by excessive drag while pulling the bottomhole assembly through the section where the cuttings quit fallingWhile tripping in the hole, bridges will be encountered in this section



6060oo to 90to 90oo

Above an inclination of 60°, cuttings bed development does not get any worseA cuttings bed will build up reducing the annular area which increases the annular velocityAs the annular velocity increases, the drilling fluid will erode the bed fasterAt some point, an equilibrium will be reached between the deposition and erosion of the cuttings bed



Annular velocityAnnular velocityAnnular velocity is the variable that will affect hole cleaning the mostAs can be seen in Figure 6-18, increasing the viscosity may actually reduce hole cleaning at lower flow ratesAt higher flow rates, viscosity makes less of a difference



Annular velocityAnnular velocityAnnular velocity is the variable that will affect hole cleaning the mostAs can be seen in Figure 6-18, increasing the viscosity may actually reduce hole cleaning at lower flow ratesAt higher flow rates, viscosity makes less of a difference0

10

20

30

40


Cut

tings

Con

cent

ratio

n

Turb. Water 115'/min Turb. Mud 115'/min Lam. Mud 115'/min

Lam. Mud 172'/min Turb. Mud 229'/min Lam. Mud 229'/min




Fluids in turbulent flow have relatively flat velocity profiles; whereas, the laminar velocity profile is much more pointed In laminar flow, there can be a significant difference between the velocity of the fluid in the center of the annular space as compared to the velocity near the pipe and hole walls

Laminar Turbulent



Pipe movementPipe movementDrill pipe movement is an important hole cleaning consideration in directional wells Both rotation and reciprocation will increase the hole cleaning capacity in a directional wellWhen reciprocating the drill pipe, the annular velocity around the tool joint increases aiding hole cleaning



As an example, if the annular velocity in a 4 1/2 by 8 1/2” (114.3 x 215.9 mm) annulus is 120 fpm (37 mpm), then the annular velocity around 6 1/4” (158.8 mm) tool joints would be 208 fpm (63 mpm) or a 73 percent increase



Rotation will also aid hole cleaning



While drilling with a steerable system in the oriented mode (slide mode), the drag in a horizontal well increasedAfter returning to rotation the drag in the well decreased In this case, the increased drag was due to a cuttings buildup in the well



Pipe eccentricity will affect hole Pipe eccentricity will affect hole cleaning but the position of the pipe cleaning but the position of the pipe in the wellbore cannot be easily in the wellbore cannot be easily changedchangedCentered pipe exhibits the best hole Centered pipe exhibits the best hole cleaning, but the pipe is almost never cleaning, but the pipe is almost never in the center of the hole in a in the center of the hole in a directional welldirectional well



With a fluid in With a fluid in laminar flow, the laminar flow, the velocity on the velocity on the narrow side of the narrow side of the annulus is lower annulus is lower than the velocity than the velocity on the wide side of on the wide side of the annulusthe annulus



As in vertical wells, washouts will As in vertical wells, washouts will impair hole cleaningimpair hole cleaningThe annular velocity in a washout The annular velocity in a washout will be reduced making hole cleaning will be reduced making hole cleaning more difficultmore difficult



If the washout is at an inclination of If the washout is at an inclination of 3535°° to 55to 55°°, the cuttings accumulation , the cuttings accumulation can slide down the hole when the can slide down the hole when the pump is turned offpump is turned offHole cleaning in formations that are Hole cleaning in formations that are sensitive to hole erosion can be sensitive to hole erosion can be difficult difficult The high annular velocities required The high annular velocities required to clean a directional well can to clean a directional well can enlarge the hole causing a reduction enlarge the hole causing a reduction in annular velocity in annular velocity

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However, it should be remembered However, it should be remembered that the formation of a cuttings bed that the formation of a cuttings bed will reduce annular volume causing will reduce annular volume causing an increase in annular velocity an increase in annular velocity anyway, which can still lead to anyway, which can still lead to erosionerosion



Though not directly related to hole Though not directly related to hole cleaning, barite sag can also be a cleaning, barite sag can also be a problem in a directional wellproblem in a directional wellBarite sag results from Barite sag results from gravitationally induced settling of the gravitationally induced settling of the barite to form either a density barite to form either a density gradient or a barite sedimentation gradient or a barite sedimentation bedbedThe drilling fluid should have enough The drilling fluid should have enough viscosity to keep the barite viscosity to keep the barite suspendedsuspended



SummarySummaryThe hole cleaning principals of vertical wells applies to directional wells with inclinations below 10°



For wells with inclinations between 10° and 30°, hole cleaning is affected by the possible deposition of a cuttings bed on the low side of the hole. Because the cuttings bed will slide down the hole even with the pump on, the cuttings eventually end up back in the flow stream. Slightly higher annular velocities are required in these wells and increasing the viscosity and yield point will help.



The most difficult section of a directional well to clean is between 30°and 60°. A cuttings bed will be formed on the low side of the hole unless the annular velocity is sufficient to erode the bed. A cuttings bed can slump after the pump is turned off causing excessive torque and drag or a stuck drill string. Increasing the annular velocity will aid hole cleaning more than anything else. Thin fluids pumped in turbulent flow will clean the best, though water will not clean as good as a low viscosity mud



In wells with inclinations greater than 60°, high annular velocities are required. In reality, the section of the hole greater than 60° is easier to clean than the section from 30° to 60°. Therefore, the fluid should be designed to clean the build section from 30° to 60°.



Field experience shows that pipe movement significantly aids hole cleaning. While circulating to clean the hole, the pipe should be both reciprocated and rotated. Reciprocation should be greater than the length of a joint of drill pipe



With a top drive, it is possible to With a top drive, it is possible to circulate and back ream the holecirculate and back ream the holeBack reaming will keep the cuttings Back reaming will keep the cuttings above the bit until the inclination above the bit until the inclination reduces to approximately 60reduces to approximately 60°°At inclinations lower than 60At inclinations lower than 60°°, the , the cuttings may slide past the bit while cuttings may slide past the bit while circulation is interrupted to make a circulation is interrupted to make a connectionconnection



In high angle directional wells, In high angle directional wells, hydraulics may have to be sacrificed hydraulics may have to be sacrificed to achieve the annular velocities to achieve the annular velocities necessary to clean the holenecessary to clean the holeA minimum annular velocity of 200 A minimum annular velocity of 200 fpm (61 fpm (61 mpmmpm) would require 386 gpm ) would require 386 gpm (1.46 m(1.46 m33pm) in an 8 pm) in an 8 ½”½” by 5by 5”” (215.9 x (215.9 x 127.0 mm) annulus and 1021 gpm 127.0 mm) annulus and 1021 gpm (3.86 m(3.86 m33pm) in a 12 pm) in a 12 ¼”¼” by 5by 5”” (311.2 x (311.2 x 127.0 mm) annulus127.0 mm) annulus



386 gpm (1.46 m386 gpm (1.46 m33pm) is well within the pm) is well within the limits of a 6 limits of a 6 ¼”¼” (158.8 mm) motor while (158.8 mm) motor while 1021 gpm (3.86 m1021 gpm (3.86 m33pm) exceeds the upper pm) exceeds the upper limit of an 8limit of an 8”” (203.2 mm) motor(203.2 mm) motorIn order to achieve the higher flow rates, a In order to achieve the higher flow rates, a byby--pass would be required in the 8pass would be required in the 8”” (203.2 (203.2 mm) motor or use a larger motor (9 mm) motor or use a larger motor (9 ½”½”))If the hole is prone to washouts, the pump If the hole is prone to washouts, the pump rate may need to be even higherrate may need to be even higher

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