guidelines for effective hole cleaning in directional wells

GUIDELINES TO EFFECTIVE HOLE CLEANING - DR. S. V. DOSHI 1

GUIDELINES FOR EFFECTIVE

HOLE CLEANING

DR. S V DOSHI


THE ESSENTIALS

TWO PRIMARY ACTIVITIES ASSOCIATED WITH DRILLING A WELL

1. PENETRATING SUBTERRANEAN FORMATIONS WITH THE

DRILL BIT. 2. REMOVING THE DRILLED

MATERIAL FROM THE HOLE THUS DRILLED


HOLE CLEANING

THIS LATTER PROCESS WHICH WE CALL HOLE CLEANING DOES NOT GET THE ATTENTION IT DESERVES

WE MERELY ASSUME THAT THE ACT OF CIRCULATING DRILLING MUD UP AND DOWN THE HOLE CAN TAKE CARE OF THIS ACTIVITY.

THIS MAY SOMETIMES BE TRUE IN VERTICAL WELLS BUT IT IS SELDOM THE CASE IN DRILLING HIGH ANGLE DEVIATION WELLS


HIGH ANGLE DEVIATED WELLS

IN THESE HIGH ANGLE DEVIATED WELLS THE CUTTINGS FOLLOW A COMPLEX AND TORTUROUS PATH TO THE SURFACE IN WHICH SOME OF THE CUTTINGS GRAVITATE TO THE LOW SIDE OF THE HOLE.

FAILURE TO CLEAN THESE CUTTINGS OUT OF THE BOREHOLE LEADS TO MANY SERIOUS PROBLEMS WE ENCOUNTER IN THESE WELLS.


WHAT IS THIS PRESENTATION ABOUT?

This presentation is intended to serve as a

guideline to effective hole cleaning.

GOOD HOLE CLEANING DOES NOT JUST HAPPEN –

YOU HAVE TO MAKE IT HAPPEN.


HOLE CLEANING EFFICIENCYTHE RATIO OF THE RATE AT WHICH THE

CUTTINGS ARE REMOVED FROM THE HOLE TO THE RATE AT WHICH THEY ARE GENERATED AT THE BIT IS THE HOLE CLEANING RATIO.

IDEALLY WE WOULD LIKE THIS TO BE = 1.

BUT IT WOULD BE A COINCIDENCE IF THIS WERE TO ACTUALLY HAPPEN – YOU HAVE TO BE LUCKY TO GET THIS IDEAL SCENARIO.

NORMALLY THE RATE OF CUTTING REMOVAL LAGS THE RATE OF CUTTING GENERATION


HOLE CLEANING EFFICIENCY

THIS LAGGING BEHIND LEADS TO ACCUMULATION OF SOME CUTTINGS IN THE HOLE.

SO LONG AS THIS ACCUMULATION DOES NOT HAMPER NORMAL OPERATIONS YOU CAN TOLERATE IT. BUT WHEN THIS ACCUMULATION STARTS HAMPERING OUR NORMAL OPERATIONS WE ARE IN TROUBLE.


CUTTINGS REMOVAL - 1

CUTTINGS CAN BE DEGRADED CHEMICALLY AND PHYSICALLY WHILE STILL IN THE ANNULUS.

DEGRADATION/DISPERSION OF THE CUTTING IN THE ANNULUS MUD STREAM DECREASES THE SIZE OF THE CUTTINGS LEADING TO AN IMPROVEMENT IN THE HOLE CLEANING EFFICIENCY


CUTTINGS REMOVAL – 2

DISPERSION OF CUTTINGS INTO THE MUD STREAM CAN HAVE SERIOUS UNDESIRABLE EFFECTS ON THE PROPERTIES OF THE MUD.

SOBMs DO NOT ALLOW THE CUTTINGS TO DISPERSE IN THE MUD OR DEGRADE IN THE MUD AND HENCE THEIR HOLE CLEANING EFFICIENCIES ARE LESS AS COMPARED TO WATER BASED MUDS WHICH AID DISPERSION OF CUTTINGS.


SYMPTOMS OF INADEQUATE HOLE CLEANING

SMALL VOLUME OF CUTTINGS AT THE SHAKER AS COMPARED TO THE VOLUME OF THE HOLE DRILLED.

LARGE AMOUNT OF FILL AFTER TRIPS

INCREASING DRAG

INCREASING TORQUE

REGROUND (SMALL AND ROUNDED) CUTTINGS

INCREASED ECD AS MEASURED BY THE PWD TOOL


PROBLEMS RELATED TO INADEQUATE HOLE CLEANING

LOST CIRCULATION DUE TO PACK OFF OR HIGH ECD

STUCK PIPE

HIGH TORQUE AND DRAG

DIFFICULTIES IN RUNNING AND CEMENTING CASING

DIFFICULTY IN GETTING THE LOGGING TOOLS TO THE REQUIRED DEPTH


FACTORS AFFECTING HOLE CLEANING

HOLE SIZE

HOLE ANGLE

ROP

FLOW RATE

DRILLING FLUID PROPERTIES

PIPE ROTATION

CUTTINGS SIZE AND SHAPE

MINERALOGY OF THE CUTTINGS


BEHAVIOR OF THE CUTTINGS IN THE WELL

BORE THE BEHAVIOR OF CUTTINGS IN THE

WELL BORE IS LARGELY DEPENDENT ON THE ANGLE OF INCLINATION OF THE WELL BORE

WE CAN CLASSIFY WELL BORES INTO THREE TYPES› STRAIGHT OR NEAR STRAIGHT 0 -

300

› HIGH ANGLE HOLES30 - 650

› EXTREMELY HIGH ANGLE HOLES 65 - 900


BEHAVIOR OF THE CUTTINGS IN THE WELL

BORE DRILL CUTTINGS EXHIBIT

DISTINCTLY DIFFERENT BEHAVIOR IN EACH OF THESE HOLE TYPES

EACH WELL TYPE REQUIRES DIFFERENT CONSIDERATIONS WITH RESPECT TO EFFICIENT HOLE CLEANING.

15

STRAIGHT HOLE 0 – 30O

THE MOTION OF THE CUTTINGS

IS THE STRAIGHT HOLE

IS LARGELY DOWNWARD

WHEN THERE IS NO

CIRCULATION AND UPWARD

WITH CIRCULATION

GUIDELINES TO EFFECTIVE HOLE CLEANING - DR. S. V. DOSHI


THE VECTOR OF THE DOWNWARD MOTION IS CONTROLLED BY THE FORCE OF GRAVITY AND IS INFLUENCED BY:• BUOYANCY• VISCOSITY OF THE DRILLING FLUID• SIZE OF THE PARTICLE

THE UPWARD MOTION OF THE PARTICLE IS GOVERNED BY ALL OF THESE AND BY THE VELOCITY OF THE DRILLING FLUID.

THE MATTER OF HOLE CLEANING IS A MATTER OF SUFFICIENT CIRCULATION OF THE WELLBORE


HI ANGLE WELLS 30 – 650

LIFE BECOMES SLIGHTLY COMPLEX HERE DUE TO THE TENDENCY OF THE CUTTINGS TO SETTLE ON THE LOW SIDE OF THE HOLE EVEN WHEN MOVING UP DUE TO CIRCULATION OF THE MUD.

THE AVALANCHING OF THE CUTTINGS IN THESE HOLESMAKES THEM THE MOST DIFFICULT TO CLEAN.


EXTREME HOLE ANGLES 65 – 90O

CUTTINGS TEND TO SETTLE ON THE LOW SIDE OF THE HOLE BUT WHEN CIRCULATION IS STOPPED

THE CUTTING DO NOT AVALANCHE DOWN THE WELLBORE WHEN CIRCULATION IS STOPPED


HOLE CLEANING CONSIDERATIONS

ANNULAR VELOCITY HIGHER THE BETTER IS A GOOD

RULE OF THUMB PROVIDED THE FORMATIONS ARE COMPETENT

IN STRAIGHT HOLES MUD VISCOSITY AND ANNULAR VELOCITY ARE THE ONLY CONSIDERATIONS.


ANNULAR VELOCITY - 1

FOR HIGH ANGLE AND EXTREME HIGH ANGLE WELLS IT IS NECESSARY TO OPTIMIZE THE ANNULAR VELOCITY WITH THE HIGHEST PRACTICAL FLOW RATE

BUT THIS FACTOR WILL NOT OBTAIN ADEQUATE HOLE CLEANING.


ANNULAR VELOCITY - 2

RECOMMENDED MINIMUM FLOW RATES AND ANNULAR VELOCITIES

HOLE SIZE INCHES

FLOW RATE GPM

ANNULAR VELOCITY

FT/MIN

17 1/2 900 – 1200 76 – 100

12 1/4 700 – 1000 133 – 190

9 7/8 600 – 850 197 – 279

8 1/2 400 - 600 202 - 303


HOLE SIZEHOLE SIZE IS A MAJOR FACTOR IN HOLE CLEANING. ANNULAR

VELOCITY OF 140 FT/MIN OR MORE IS HIGHLY DESIRABLE IN

HIGH ANGLE WELLS BUT THESE RATES CAN BE ACHIEVED ONLY IN SMALLER HOLES

HOLE SIZE

CHARACTERISTICS

17 ½ AND

LARGER

EXTREMELY DIFFICULT TO CLEAN. PROBLEM COMPOUNDED BY USE OF SOBMs. LUCKILY WE DON’T USE SOBMs IN THESE SECTIONS. ALL AVAILABLE TOOLS AT HAND MUST BE BROUGHT INTO PLAY TO CLEAN THE HIGH ANGLE WELLS OF THIS SIZE

14 ¾ AND 12

¼

HOLE CLEANING REMAINS A PROBLEM IN THESE HOLE SIZES TOO. SOBMs ARE FREQUENTYLY USED IN THESE SECTIONS COMPOUNDING HOLE CLEANING PROBLEMS.

9 7/8HOLE CLEANING BECOMES EASIER IN THESE SECTIONS IF GOOD PRACTICES ARE FOLLOWED.


HOLE ANGLE

STRAIGHT HOLES CAN BE CLEANED WITHOUT MUCH

EFFORT.

HIGH ANGLE WELLS ARE DIFFICULT TO CLEAN BECAUSE OF THE TENDENCY OF

CUTTINGS TO SETTLE ON THE LOW SIDE OF THE HOLE AND THE FLUID CIRCULATION

PROFILE IN THESE KINDS OF WELLS


FLOW PROFILE IN HIGH ANGLE WELLS

THE DRILL PIPES AND CUTTINGS LIE ON THE LOW SIDE OF THE HOLE.

THE AREA OF THE HIGHEST FLUID VELOCITY TENDS TO BE AT THE HIGH SIDE OF THE HOLE WHILE THE LOW SIDE CONTAINS AN AREA OF LOW FLOW RATE THAT IS EFFECTIVELY A DEAD ZONE


CROSS SECTION IN A HIGH ANGLE HOLE

THIS TYPE OF FLOW PROFILE CREATES HUGE PROBLEMS WHEN THE

CUTTINGS SETTLE INTO A SPACE OF LITTLE OR NO FLOW ON THE LOW SIDE

OF THE HOLE.THE EFFECT GETS MORE PRONOUNCED AS THE

PIPE ECCENTRICITY INCREASES

THE CLEANING DEPENDS ON REMOVING THE

CUTTING FROM THE LOW SIDE OF THE HOLE INTO

THE AREA OF HIGH FLOW. D/P ROTATION IS THE

MOST EFFECTIVE TOOLS FOR ACHIEVING THIS.


CUTTINGS TRANSPORT IN A HIGH ANGLE HOLE -

1 THE CUTTINGS MOVE UP-HOLE INTO

THE HIGH FLOW AREA UNTIL THEY ONCE MORE SETTLE INTO THE DEAD SPACE ON THE LOW SIDE OF THE HOLE.

THEN THEY ARE THROWN INTO THE MAIN STREAM BY THE ROATION OF THE D/P

THIS START STOP PRACTICE CONTINUES UNTIL THE CUTTINGS REACH THE STRAIGHT HOLE SECTION AND ARE CIRCULATED OUT


CUTTINGS TRANSPORT IN A HIGH ANGLE WELL -

2 THE CUTTINGS IN THE START-STOP MOTION

ARE ABRADED MECHANICALLY BY THE D/P ROTATION AND BECOME SMALLER AND ROUNDED.

THIS UP AND DOWN JOURNEY IS SLOW AND TAKES LONGER THAN THE BOTTOMS UP TIME EVEN WITH OPTIMUM D/P ROTATION.

WITHOUT D/P ROTATION THE CUTTINGS BED MAY REMAIN IN PLACE WITH VERY LITTLE UPWARD MOTION AND MAY EVEN SLIDE DOWNWARDS WHEN CIRCULATION IS STOPPED


CUTTINGS DELIVERY VS PIPE ROTATION


EFFECT OF PIPE ROTATION

THERE IS A GREAT DIFFERENCE IN THE CUTTINGS REMOVAL FROM 100 AND 120 RPM

A SIMILAR CHANGE OCCURS BETWEEN 150 AND 170 RPM

OPTIMUM PIPE ROTATION IS THE SINGLE MOST EFFECTIVE WAY TO OBTAIN SIGNIFICANT INCREASES IN HOLE CLEANING


RECOMMENDED MINIMUM PIPE ROTATION SPEEDS

HOLE SIZE – (INCHES) MINIMUM PIPE ROTATION SPEED RPM

17 1/2 120

12 1/4 120

9 7/8 120

8 1/2 80


DRILLING FLUID VISCOSITY 1STRAIGHT HOLES

INCREASING VISCOSITY TO CLEAN THE HOLE USUALLY WORKS IN A STRAIGHT HOLE.

17 ½”AND 20” HOLES ARE GENERALLY DRILLED WITH A LOW MUD WEIGHT SO THEY CAN BE CLEANED BY INCREASING THE VISCOSITY OF THE MUD WHERE Yp > Pv IN ORDER TO OVERCOME THE LOW BUOYANCY AND THE LOW ANNULAR VELOCITY OF THE MUD.


DRILLING FLUID VISCOSITY 2

IN SMALLER HOLES MUD WT. AND ANNULAR VELOCITY INCREASE AND HOLE CLEANING IMPROVES ACCORDINGLY.

IN SMALLER HOLES ECD IS ALSO AN IMPORTANT FACTOR TO BE CONSIDERED IN DETERMINING THE OPTIMUM VISCOSITY OF STRAIGHT HOLES.

HIGHER ANNULAR VELOCITY ALLOWS FOR USE OF LOVER FLUID VISCOSITY WITHOUT COMPROMISING THE CLEANING EFFICIENCY.


THE EFFECT OF VISCOSITY IN HIGH

ANGLE HOLES

HIGH VISCOSITY DOES NOT NECESSARILY PROMOTE IMPROVED HOLE CLEANING IN DEVIATED HOLES.

BOTH HI VIS AND LOW VIS ARE DETRIMENTAL TO HOLE CLEANING IN THESE WELLS.

A RANGE OF MODERATE VISCOSITY PROMOTES THE BEST HOLE CLEANING.


THE EFFECT OF VISCOSITY IN HIGH ANGLE HOLES - 1



THE INCREASE IN THE VISCOSITY AS MEASURED BY THE 6 RPM READING OF THE FANN VISCOMETER, ABOVE A CERTAIN LEVEL ONLY SERVES TO ENLARGE THE DEAD ZONE AREA ON THE LOW SIDE OF THE HOLE WHICH ONLY SERVES TO MAKE THE HOLE CLEANING MORE PROBLEMATIC


HI VISCOUS SWEEPS

HIGH VISCOUS SWEEPS CAN BE EFFECTIVE IN STRAIGHT HOLES BUT THEY ARE NOT VERY HELPFUL IN HI ANGLE HOLES.

IN FACT THEY CAN BE DETRIMENTAL TO HOLE CLEANING IN HI ANGLE HOLES

THIS IS DUE TO THE FACT THAT HI VIS SWEEPS CAN ENLARGE THE DEAD ZONE ON THE LOW SIDE OF THE HOLE


HI DENSITY SWEEPS - 1

HIGH DENSITY SWEEPS ARE VERY EFFECTIVE IN REMOVAL OF CUTTING BEDS AND HAVE BECOME STANDARD PRACTICE IN THE DRILLING OF HI ANGLE HOLES.

THEY ARE TYPICALLY WEIGHTED UP 1 TO 3 PPG (0.12 TO 0.36 SG) OVER THE BASE MUD AND VISCOSITY IS NOT INCREASED BEYOND WHAT THE ADDITIONAL WEIGHING MATERIAL CONTRIBUTES.



THESE SWEEPS ARE SMALL IN VOLUME (30-50 BBL) USUALLY 200 – 500 FT OF ANNULAR HEIGHT.

SO THE DANGER OF INCREASING THE HYDROSTATIC HEAD OF THE MUD COLUMN AS THE SWEEP MOVES UP THE ANNULUS IS AVOIDED.

LARGE SWEEPS ARE ALSO PROBLEMATIC WHEN THE CUTTING BEDS ARE LARGE.



THIS IS BECAUSE THE SWEEP CAN PICK UP ENOUGH MATERIAL TO OVERLOAD THE ANNULUS WITH CUTTINGS CREATING A POTENTIAL PACK OFF.

HENCE IT IS A GOOD IDEA TO USE A SMALLER HI DENSITY SWEEP AND CIRCULATE OUT THE CUTTINGS BEFORE GOING IN FOR ANOTHER SWEEP.

GOOD SHALE SHAKER DISCIPLINE IS REQUIRED HERE, TO BE AWARE OF THE CUTTINGS COMING OUT BEFORE SWEEPING THE HOLE WITH THE NEXT HI DENSITY SWEEP


HIGH DENSITY SWEEPS - 4

SOMETIME BACK I HAD TALKED OF VERY FINELY GROUND BARITE – THE WARP WHILE WE WERE DISCUSSING BARITE SAG.

NOW I WILL TALK ABOUT VERY COARSE GROUND BARITE IN MAKING THESE HIGH DENSITY SWEEPS.

IT HAS BEEN FOUND THAT COARSE BARITE IS MORE EFFECTIVE THAN NORMAL BARITE THAT IS USUALLY USED IN WEIGHING UP THE MUD.



THE SCOURING EFFECT OF THE COARSE BARITE IS THOUGHT TO PLAY A ROLE IN THE INCREASED EFFICIENCY OF COARSE BARITE TO REMOVE THE CUTTING BEDS.

“SWEEP WATE” IS A PATENTED PRODUCT BY BAROID WHICH IS EMPLOYED IN MAKING THESE HIGH DENSITY SWEEPS.

COARSE NUT HULLS ARE ALSO EMPLOYED IN THE PREPARATION OF HIGH DENSITY SWEEPS.



THE OTHER ADVANTAGE OF USING COARSE MATERIAL IS THAT THIS CAN BE PARTIALLY REMOVED BY THE SOLIDS CONTROL EQUIPMENT AT THE SURFACE.

SO THE INCREASE IN THE MUD WEIGHT DUE TO FREQUENT USE OF THESE SWEEPS IS MINIMIZED.

WITH NORMAL GROUND BARITE EMPLOYED FOR THE HIGH DENSITY SWEEPS, DILUTION BECOMES NECESSARY.



DILUTION HIGH VOLUMES HIGH COSTS

DISADVANTAGES



ONE SHOULD HAVE A REGULAR PROGRAM FOR EMPLOYING THESE HIGH DENSITY SWEEPS.

FREQUENCY DEPENDS ON THE HOLE SIZE AND ROP

TYPICALLY THESE SWEEPS ARE EMPLOYED FOR EVERY 1-3 STANDS DRILLED.


FREQUENCY OF HI DENSITY SWEEPS

HIGH DENSITY SWEEPS (1-3 BBL OVER THE BASE MUD

WEIGHT)17 ½” HOLE 50 – 60 BBL SWEEP

EVERY 1-2 STANDS

12 ¼ ” HOLE 30 – 40 BBL SWEEP EVERY 1 – 3

STANDS

8 ½ ” HOLE 20 – 30 BBL SWEEP EVERY 3 – 5

STANDS



IT IS IMPORTANT TO CIRCULATE AT DRILLING FLOW RATE WITH OPTIMUM PIPE ROTATION DURING THE ENTIRE TIME THE SWEEP IS IN THE HOLE.

FOR FLOATING DRILLING RIGS WITH SUB SEA STACKS, THE SWEEP NEED ONLY BE IN THE RISER WHEN CIRCULATION THROUGH THE DRILL STRING STOPS. A BOOSTER PUMP CAN BE EMPLOYED TO KEEP THE SWEEP IN THE RISER MOVING UPWARDS.


THE CUTTING BED - 1 CUTTING BEDS ARE FREQUENTLY

COMPOSED OF VERY FINE PARTICLES DUE TO THE GRINDING EFFECT OF THE BHA AND THE DRILL PIPE.

CUTTING BEDS ALSO CONTAIN BARITE WHICH HAS SAGGED TO THE LOW SIDE OF THE HOLE IF THE WEIGHTED MUDS ARE BEING USED.

THESE FINE MATERIALS MAY NOT BE VISIBLE ON THE SURFACE UNLESS VERY FINE SHALE SHAKER MESHES (> 175 MESH) ARE EMPLOYED.


THE CUTTING BED - 2

SOLIDS CONTENT OF THE RETURNS AT THE FLOW LINE AS COMPARED TO THE PRE SWEEP CONTENT IS A GOOD INDICATION OF THE CUTTINGS LOAD RETURNED BY THE SWEEP.

THE REDUCTION OR ELIMINATION OF THE SYMPTOMS OF INADEQUATE HOLE CLEANING IS THE BEST EVIDENCE THAT THE SWEEP PROGRAM HAS BEEN EFFECTIVE.


EXTENDED CIRCULATION

IN HIGH ANGLE WELLS BOTTOMS UP OF THE MUD IS NOT THE BOTTOMS UP FOR THE CUTTINGS.

EXTENDED CIRCULATION TIMES ARE THEREFORE NECESSARY FOR GOOD HOLE CLEANING EFFICIENCY.

THIS HAS TO BE ACCEPTED WITHOUT RESERVATION IN OPERATIONS ON THIS TYPE OF HOLE.


DURING DRILLING THE HOLE SHOULD BE CIRCULATED WITH

D/P ROTATION FOR AT LEAST 10 – 15 MIN BEFORE MAKING A CONNECTION TO MOVE THE CUTTINGS AWAY FROM THE BHA BEFORE CIRCULATION IS STOPPED.

WHEN DRILLING WITH VERY HIGH ROP OR AFTER SLIDING A KELLY LENGTH SYMPTOMS LIKE JERKY TORQUE AND FLUCTUATING PUMP PRESSURE ARE SURE SHOT INDICATORS THAT EXTENDED CIRCULATION IS NEEDED TO FLUSH THE HOLE OF EXCESSIVE CUTTINGS.


CIRCULATION TIMES

HOLE TYPECIRCULATION TIME PRIOR

TO TRIPS

0 – 30o1.2 TO 1.8 TIMES BOTTOMS

UP


UP


UP

THE HOLE MUST BE CIRCULATED CLEAN PRIOR TO TRIPS AND THIS MAY TAKE

AS MUCH AS 4 TIMES THE BOTTOMS UP FOR SOME HIGH ANGLE WELLS.


IMPORTANT

IT IS IMPORTANT TO REMEMBER THAT THESE ARE MERE GUIDELINES FOR GOOD HOLE CLEANING PRACTICES.

THE HOLE WILL NEVER BE PERFECTLY CLEAN BUT WE CAN LIVE WITH THE FACT THAT THE HOLE IS CLEAN ENOUGH TO TRIP WITHOUT EXCESSIVE OVERPULL DUE TO CUTTING BEDS.


IMPORTANT

THE ACTUAL TIME TO ACHIEVE AN EFFECTIVELY CLEAN HOLE WILL

DEPEND ON THE ANNULAR VELOCITY, DETAILED HOLE GEOMETRY, SPEED

OF PIPE ROTATION, VISCOSITY, MUD WEIGHT, CUTTING MINERALOGY, INHIBITIVE CHARACTERISTICS OF

THE MUD AND THE COARSENESS/FINENESS OF THE

WEIGHING MATERIAL


IMPORTANT

AS YOU CAN SEE THESE ARE ALL VERY COMPLEX FACTORS TO PREDICT FROM SIMPLE GUIDELINES.

DON’T KEEP ANY ARBITRARY GUIDELINES – FOLLOW THE BEST PRACTICES TO ENGINEER GOOD HOLE CLEANING.

REMEMBER – GOOD HOLE CLEAN DOES NOT JUST HAPPEN – YOU HAVE TO MAKE IT HAPPEN.


BACK REAMING

WITH A TOP DRIVE SYSTEM BACK REAMING HAS BECOME A PRACTICE THAT IS EXTENSIVELY USED IN RESPONSE TO VARIOUS HOLE CONDITIONS.

BACK REAMING IS AN OUTSTANDING PROCEDURE IN STRAIGHT HOLES WHERE EXCESSIVE OVER-PULL IS MOST OFTEN DUE TO UNDER-GAUGE HOLE, LEDGES AT THE FORMATION INTERFACE OR OTHER HOLE GEOMETRY PROBLEMS


BACK REAMING

HOWEVER BACK REAMING HAS BEEN FOUND TO BE DANGEROUS IN HIGH ANGLE HOLE WELLS.

THE OVER-PULL CONDITION IS USUALLY DUE TO THE DRAGGING OF THE BIT AND THE BHA INTO A CUTTINGS BED AND BACK REAMING CAN RESULT IN A CUTTING LOAD SO HIGH THAT IT MAY BURY THE BIT AND THE BHA.

PACK OFF WITH LOST CIRCULATION AND/OR STUCK-PIPE IS OFTEN THE RESULT


OVER-PULL - WHAT TO DO?

IF OVER-PULL IS EXPERIENCED DURING TRIPPING IN HIGH ANGLE HOLES THE FIRST RESPONSE SHOULD BE TO RUN BACK INTO HOLE 2-3 STANDS AND CIRCULATE WITH OPTIMUM PIPE ROTATION FOR AT LEAST 30 MIN.

THE TRIP OUT CAN THEN BE CONTINUED AND IF OVER-PULL OCCURS AT A HIGHER POSITION THEN IT CAN BE ASSUMED TO BE DUE TO A CUTTINGS BED AND THE PROCEDURE SHOULD BE REPEATED.


OVER-PULL - WHAT TO DO?

IN CASE THE OVER-PULL OCCURS REPEATEDLY AT THE SAME PLACE IT CAN BE ASSUMED TO BE DUE TO A LEDGE OR A KEYSEAT AND THEN CAN BE WORKED WITH BACK-REAMING

IN SPITE OF THE DANGER FROM CUTTING BEDS BACK-REAMING REMAINS A USEFUL PRACTICE.

BUT IT SHOULD NOT BE USED AS THE RESPONSE OF FIRST RESORT IN HIGH ANGLE WELLS.


SUMMATION

KEEP A COMPREHENSIVE PROGRAM FOR MUD CLEANING HANDY AT ALL TIMES

THE FACTORS TO BE CONSIDERED ARE:

FLOW RATE

PIPE ROTATION

HI DENSITY SWEEPS

EXTENDED CIRCULATION


Thank You Very Much

guidelines for effective hole cleaning in directional wells

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