15 drilling instrumentation

8/22/2019 15 Drilling Instrumentation

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Breakdown and drillingproblems

Matanovi Davorin, professor

Faculty of mining, geology and petroleumengineering, Zagreb


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IntroductionWellbore stability is theprevention of brittle failure orplastic deformation of the

rock surrounding thewellbore due to mechanicalstress or chemical imbalance.

Prior to drilling the mechanicalstresses in the formation areless than the strength of therock.

The chemical action is alsobalanced, or occurring at a raterelative to geologic time.

Rocks under this balanced or

near balanced state are stable.


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Introduction

After drilling, the rock surrounding thewellbore undergoes changes in tension,compression, and shear loads as the rockforming the core of the hole is removed.

Chemical reaction also occur with exposureto the drilling fluid.


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IntroductionUnder these conditions therock surrounding thewellbore can becomeunstable, begin to deform,fracture, and cave into the

wellbore or dissolve into thedrilling fluid.Excessive rock stress cancollapse the hole resulting in

stuck pipe.Hole-squeezing mobileformations produce tight holeproblems and stuck pipe.

Cavings from failing formationmakes hole cleaning moredifficult and increases mud andcementing costs.

Wellbore

Pressure

(a)

(b)

BRITTLE

SHALE

SALT

FRIABLE

SANDSTONEOVERGAUGE

HOLE

LOST

CIRCULATION

HOLE

CLOSURE


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IntroductionFishing is the process of removing a fish orjunk from the borehole.

A fish is a part of the drill string (tubing, suckerrods, wire, rope or cable) that separates from theupper remaining portion of the drill string whilethe drill string is in the well.

This can result from the drill string failingmechanically, or from the lower portion of the drillstring becoming stuck or otherwise becomingdisconnected from drill string upper portion.

Such an event will instigate an operation to freeand retrieve the lower portion (or fish) from thewell with a strengthen specialized string


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Junk is usually described as small items ofnon-drillable metals that fall or are left behindin the borehole during the drilling,

completion, or workover operations.These non-drillable items must be retrieved beforeoperations can be continued.

It is important to remove the fish or junk from thewell as quickly as possible.

The longer these items remain in a borehole, themore difficult these parts will be to retrieve.

Further, if the fish or junk is in an open holesection of a well the more problems there will bewith borehole stability.

Introduction


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There is an important tradeoff thatmust be considered during any fishingoperation.

Although the actual cost of a fishingoperation is normally small compared tothe cost of the drilling rig and other

investments in support of the overalldrilling operation, if a fish or junk cannotbe removed from the borehole in a timely

fashion, it may be necessary to sidetrack(directionally drill around the obstruction)or drill another borehole.

Introduction


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Thus, the economics of the fishing

operation and the other incurred costsat the well site must be carefully andcontinuously assessed while the fishing

operation is underway.It is very important to know when toterminate the fishing operation and get onwith the primary objective of drilling a well.

Introduction


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IntroductionThe number of days that should beallowed for a fishing (D

f) operation

is:

Where:

Vf

the replacement value of the fish(dollars or other money)

Cs estimated cost of the sidetrack or

the cost of restarting the well(money)

Rf the cost per day of the fishing tooland services (money/day)

Cd the cost per day of the drilling rig(and appropriate support)(money/day)

df

sff

CRCVD

++=


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The most causes of fishing jobs, notnecessarily in order of frequency, are::

1. twist off, a parting of the drill stringcaused by metal fatigue or washout;

2. stickingof the drill string;

3. bit and tool failures; and

4. foreign objects such as hand tools,

logging instruments, and brokenwireline or cable lost in the hole.

Introduction


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TwistoffTwist off is the result of:rough pipe handling,faulty drill string,

stress reversals in a sharply

deviated hole drilling with drillpipe in compression,

poorly stabilized drill collars

scarring by tong dies,

improper makeup torque,

erosion caused by washout, and

other damage that create weakspots where cracks can form andenlarge under the constantbending and torque stresses of

routine drilling.


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Twist offThe pipe often separates in ahelical break or in a long tearor split.

Surface signs of a twist offinclude:

loss of drill string weight,

lack of penetration,reduced pump pressure,

increased pump speed,

reduced drilling torque, andincreased rotary speed.


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Stuck pipeThere are two general categories of drill stringsticking:

mechanical and

differential.

In mechanical sticking, the drill string is lodged inplace by solid material.

In differential sticking, the cause is pressure

difference of fluid column in the hole andformation pressure.


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Among the ways the drillstring can becomemechanically stuck are thefollowing:

Sloughing hole;that results from shale absorbingwater from the drill fluid,expanding, sloughing off, and

falling downhole.Large masses may lodge arounddrill collars and stabilizers,sticking the drill string andblocking circulation.

Abnormally pressured shale,steeply dipping shale beds, anderosion by drilling fluid can alsocause hole wall to cave in.


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Pipe stuck in under gaugeholeoften happens in shaleformations.

If the formation swells but doesnot slough off, the deformedlayer may close around the drill

pipe, cutting off circulation andpreventing passage of the tooljoints, drill collars, or bit.

A buildup of mud solids canhave the same effect, especiallyin a permeable zone where

water is lost to the formation.


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Blowout stickingoccurswhen a large volume of

sand or shale is driven uphole by formation fluidsentering the wellbore.


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Inadequate hole cleaning that is,

failure of the circulating system to

clean cuttings or other materialfrom the hole

can result from sloughing shale,

drill string washout above the bit,a low circulation rate in a large holehaving unweighted mud,

or lost returns.

Inadequate hole cleaning permitsa buildup of solids around the bitand collars. (cuttings, washout)

CUTTINGS

WASHOUT


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Key seatingoccurs when drill pipe

in tension wears an under gaugegroove in the wall of a curvedsection, or dogleg, of the hole.

When the drill string is raised orlowered, tool joints or drill collarsmay become lodged in the lower or

upper end of the key seat.


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Junk in the holesuch asmetal fragments or broken-offor dropped equipment, may

lodge between the hole wall anddrill pipe, tool joints, or drillcollars.

Except when the drill string pullsaround the object or the objectcan be pushed into the hole wall,serious fishing problems candevelop.

This is especially true if the drillpipe gets jammed to one side in acased hole.

(Never leave the holeunprotected or leave

loose objects lyingaround the rotary area.)


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Bit stuck in tapered holeisthe result of drilling with wornbit (under gauge) in hard,abrasive formations.

Tripping in a new bit withoutreaming it to bottom can jam itpartway down the taperedsection of hole.


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Crooked pipe stacked inholeis often the result of

dropping the drill string orapplying excessive weightto stuck pipe, may jam

against the hole wall andbecome impossible toraise, lower, or rotate.


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Multiple string

wrap aroundoccurs whentubing strings

twist and wraparound each otheras they are run

into the hole.


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Differential Sticking

This is a condition in which thedrill stem becomes stuck againstthe wall of the wellbore because

part of the drill stem (usually thedrill collars) has becomeembedded in the filter cake (wallcake).

Necessary conditions fordifferential sticking are;

a permeable formation and

a pressure differential across anearly impermeable filter cake anddrill stem.

MUD CAKEDIFFERENTIAL

PRESSURE

MUD CAKE

MUD

FILTRATE

IMPERMEABLE

FORMATION

IMPERMEABLE

FORMATION

MUD

FILTRATE

PERMEABLE

FORMATION


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DifferentialSticking

Normally, the drill string is

differentially stuck when:the drill string cannot berotated, raised or lowered, butcirculating pressure is normal,

the drill collars are opposite apermeable formation, and

sticking was instantaneous when

the pipe was stationary afterdrilling fast hole.


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STUCK PIPEReferring to the varying degrees ofinabilityto move or remove the drill string from the

wellbore.Some level of sticking occurs routinely indrilling operations and these events onlybecome problematic

if the force required to initiate pipe movementexceeds what can be delivered to the stuck point.

Usually, even if the stuck condition

starts with the possibility of limited pipe rotation orvertical movement,it will degrade to the inability to move the pipe at all.


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STUCK PIPE CAUSES

1. MECHANICAL

Key seats Wellbore geometry

Inadequate hole cleaning

Under gauge borehole

Unconsolidated formations

Settled cuttings...

2. DIFFERENTIAL STICKING


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DIFFERENTIAL PRESSURE STICKING(DPS)

Is common worldwideResults in a significant amount ofnon-

productive time

May result in abandonment of the currenthole and force a sidetrack, and

Ends up as one of the major causes ofincreased well costs all over the world


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DPS - Costs

It is estimated that the cost of stuck pipe in

deep oil and gas wells can be approximately25% of the overall budget.

In some areas, events related to differentially

stuck pipe can be responsible for as much as40% of the total well cost.

The risk of differentially stuck pipeincreases when drilling depleted reservoirs

avoids when drilling underbalanced


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Differential sticking - definitionA situation in which the drilling assembly (pipe, drill collars and bottomhole assembly) is stuck in filter cake that was previously deposited

on a permeable zone.The pipe is held in the cake by a difference in pressures (P)between

the hydrostatic pressure of the mud (Pm) and the formation (pore)

pressure (Pf) in the permeable zone.

P = Pm

Pf

Differential pressure sticking is usually indicated whenthe drill string cannot be rotated, raised or lowered, butfull circulation at normal pressure can be established.

The force required to pull the pipe free can exceed the strengthof the pipe.


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DRILL STRING BEFORE AND AFTER STUCK


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DIFFERENTIAL

STICKING - CAUSES

Relatively high differentialpressure

Mud cake characteristics(thickness, permeability,lubricity..)

In the situations when it is notpossible to reduce thedifferential pressure by

reducing the mud weight theoption is to act on the mudcake.


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DIFFERENTIAL STICKING

TENDENCIES OF MUDS

.... depend on mud filter cake properties: Thickness,

Shear strength, and

Lubricity.

These filter cake properties are influenced by a combinationof variables such as: Mud overbalance

Solids content of the mud (both high-gravity and low-gravity solids)

Mud type (e.g., oil-based, polymer water-based, gel water-based),

Specific mud composition, and

Fluid loss


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MINIMIZING RISK OF STICKINGEarly detection of DPS risks could be made throughobservation of

torque and drag levels while drilling to detect any sign of deviation from a normal trend for the well.

To mitigate DPS events, operators often Minimize:

the overbalance (by decreasing mud weight) the stationary time, drilled length through low pressure formations,

Increase drill collar and drill string stabilization, and Optimize mud properties

However, despite the best efforts of operators a DPS eventmay still occur.


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PULLOUT FORCE

Pullout force needed to free a stuck pipe depends on:

F =

PA

whereF - pullout force, NP - differential pressure, PaA - contact area, m2

coefficient of friction (adhesion) between the collars andthe cake

Value of F is also increased with compressibility and thickness of the filter cake hole deviation, and diameter of the drill collars

Value of F is decreased with increase in diameter of the hole

Contact area and coefficient of friction increase

with time


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METHODS USED TO GET THE PIPE FREE

...., in addition to pulling and torquing thepipe, include:

(1) lowering hydrostatic pressure in thewellbore (by reducing the mud weight; this willreduce the differential pressure;should not beusedif well control is a problem)

(2) placing a spotting fluid next to the stuckzone and

(3) applying shock forcejust above the stuck

point by mechanical jarring, or(4) all the above.


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METHODS USED TO GET THE PIPE FREE

The most common approach, however, to getting

pipe free is to place: a spot of oil,

oil-base mud, or

special spotting fluid.

A spotting fluid (spot)

a small volume or pill of fluid placed in a wellboreannulus


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SPOTTING FLUID

MECHANISM OF ACTION

Breaks the capillary forces that holdthe drill string against the wellbore wall,

Penetrates, dehydrates, and cracks(breaks up) the filter cake, Migrates into cracks in the cake and

between the pipe and the cake, Reduces the contact (stuck) area

between pipe and wall Reduces the forces needed to work the

pipe free Increases drill string lubricity

throughout stuck zone

Allows pipe to be pulled free

Spotting fluids need to be in place asquickly as possible (within six hours afterpipe becoming stuck)

.


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SPOTTING FLUIDS

Water-based spotting fluids

Drill-in fluids (Low and ultra-low solids fluids; the sealingmechanism is generated inside the rock, leaving just a thinfilm on the outside.

Salt solutions with a low activity coefficientcombined with environmentally-safe lubricants (two-phase spot) produce low torque levels

Diesel-based spotting fluids

Synthetic-based spotting fluids

Acid based spotting fluid


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SPOTTING FLUIDS

Spotting pills:

Unweighted or

Weighted (spotting fluid + viscosifier+ weightingmaterial)

Spotting fluids (pipe-freeing agents) consist of

detergents,

soaps,

oils, surfactants and

other chemicals (wall cake cracking material).


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PIPE RECOVERY AND FREE POINT

Before placement of spotting fluid, the depth

at which the pipe is stuck must bedetermined

FREE POINT

depth to where the drill string is free and

depth where sticking starts.

This free point can be calculated usingmeasurements taken on the rig floor.


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LENGTH TO THE FREE POINT

Knowing the stretch L and the forces applied F1 and F2, Hookes law,the length of the drill string from the surface to the free point (L

f) is

whereE is the Elastic Modulus (Youngs Modulus) of steel (i.e., 200 GPa),A is the cross-sectional area of the pipe body (m2),L is the stretch distance (elastically stretch of the free portion of the

drill string (m),F1 is the force to place the entire drill string in tension (N),F2 is a force greater than F1 but less that the force limited by the yieldstress of the pipe grade (N).

12FF

LAELf

=


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Laboratory researchLaboratory tests were run to evaluate theeffectiveness of mud system additives:Carboxymethylcellulose- CMC (filtration

control additive)

Lubricant

on differential sticking tendency of thetested fluids

Selected mud: Lignosulphonate mud


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LubricantThe addition of certain lubricants to water- and oil- basedmud will

Reduce the risk of differential sticking and, should sticking stilloccur,

Reduce the force needed to free the stuck pipe or tool.

Depending on their chemical composition and state of

dispersion or solubility in the base mud, lubricants: Can coat metal surfaces, reducing the adhesion of steel to the

mud cake,

Can be incorporated into the filter cake and provide better fluid-

loss control (resulting in thinner cakes), and Can be incorporated into the filter cake to reduce the yield stress

of the cake.


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Lignosulphonate mud formulationC0, C3, C5 - CMC concentration in g/L of the mudL0, L20, L40 - lubricant concentration in ml/L of the mud

500500500500500500500500500g/LBarite

111111111ml/LDefoamer

404040202020000ml/LLubricant (Lube 167)

0,60,60,60,60,60,60,60,60,6g/LBiocide

555555555g/LViscosifer (DUO-VIS)

530530530g/LCMC

333333333g/LNaOH

202020202020202020g/LFCL (Spersen CFI)

808080808080808080g/LBentonite (MIL-GEL)

100010001000100010001000100010001000mLWater

C5L40C3L40C0L40C5L20C3L20C0L20C5L0C3L0C0L0UnitsComposition


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Spotting fluid composition

Diesel: 620 mlPipe Lax W: 80 ml

Water: 280 ml

Barite: 73 g

Spotting time: 16 hours


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Lab tests

...were carried out according to APIRecommended Practice StandardProcedure for Testing Drilling Fluids,

API RP13B:API fluid loss

Cake thickness

Rheological properties

pH value


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DIFFERENTIAL STICKING TENDENCY

...of the tested lignosulfonate mud wasevaluated using differential sticking testermarketed by OFI Testing Equipment

International.

The test device consists offiltration cell capable of holding 200 mL of fluid,perforated bottom capable of holding filter paperand screen,plate (on a plunger) andtorque wrench.

Torque necessary to break the plate free ismeasured

Test conditions:- pressure: 3 291 kPa (477.5 PSI)- temperature: room temperature


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BULK STICKING COEFFICIENT (KSC

)

The Bulk StickingCoefficient (Ksc) is

calculated by dividing theSliding Force (F

s) by the

Normal Force (Fn):

Ksc

= Fs/ F

n

For r = 1":

Ksc

= 0,001 Tu

Tu

torque (lbf-inch, 0,1129 Nm)

The Sliding Force (Fs)

of the plate is a functionof the measured torque(Tu):

Fs

= 1,5 Tu

The Normal Force (Fn)

on the plate isdetermined bymultiplying the area bythe differential pressure(This assumes that a pressure

of 477,5 PSI was used duringthe test)

Fn = 1 500 r2


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STUCK TENDENCY COEFFICIENT (Kst)

The Stuck Tendency Coefficient (Kst) isequal to the Bulk Sticking Coefficient(K

sc) multiplied by the variable stuck

area.

Kst = Ksc (Variable Stuck Area)


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LAB RESULTS - TORQUEEffect of Time on Torque

0

2

4

6

8

10

12

14

C0L0 C3L0 C5L0 C0L20 C3L20 C5L20 C0L40 C3L40 C5L40

Mud

Torque

(Nm

)

60 min

120 min

180 min

240 min

300 min

16 sati

Torque - increases with time regardless of concentration of CMC and lubricant

- decreased with increasing concentration of CMC and lubricant and- decreased after placement of spotting fluid for16-hours


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BULK STICKING COEFFICIENT

0,000

0,020

0,040

0,060

0,080

0,100

0,120

Bu

lkSticking

Coe

fficien

t


Mud

Bulk Sticking Coefficient

300 min

Sticking Time

16 hoursSpotting Time

Bulk Sticking Coefficient is decreased with increasing concentration of CMC and lubricant Bulk Sticking Coefficient of C5L40 mud is 35,3 % lesser than of C0L0 mud For C5L40 mud sticking coefficient is 2,3 times less after 16 hours spotting time

STUCK TENDENCY COEFFICIENT


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0,000

0,020

0,040

0,060

0,080

0,100

0,120

0,140


Mud

StuckTendencyC

oefficient

60 min

120 min

180 min

240 min

300 min

16 hours

Stuck tendency coefficient is increased with time regardless of concentration of CMC and

lubricant, but decreased with increasing concentration of CMC and lubricant

EFFECT OF CMC


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(MUD WITHOUT LUBRICANT)

0,000

0,020

0,040

0,060

0,080

0,100

0,120

BulkStic

kingCoefficient

60 min 120 min 180 min 240 min 300 minTime

Effect of CMC on Bulk Sticking Coefficient

0 g CMC

3 g CMC

5 g CMC

Bulk sticking coefficient of mud without lubricant and with 5 g CMC after 300 minis

9,2 % less than without CMC but 2,4 times higher than after 60 min.

EFFECT OF LUBRICANT ON


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STICKING COEFFICIENT

0,0380,0300,028

0,059

0,043

0,034

0,075

0,0540,050

0,084

0,0640,058

0,093

0,0710,066

0,000

0,010

0,020

0,0300,040

0,050

0,060

0,070

0,080

0,090

0,100

Bu

lkSticking

Coe

fficien

t

60 min 120 min 180 min 240 min 300 min

Time

Effect of Lubricant on Bulk Sticking Coefficient

of Mud with 5 g of CMC

without lubricant

2 % lubricant

4% lubricant

After 300 min test bulk sticking coefficient of mud with 5 g CMC and with 4%lubricant is 29 % less than without lubricant.

7


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FLUIDLOSS -

TORQUE

0

2

4

6

8

10

12

14


Mud

To

rque

(Nm

)

60 min 120 min 180 min 240 min 300 min 16 hour API Fluid loss-30 min (ml)

0

1

2

3

4

5

6


Mud

Fluidloss(ml)

30 min

300 min

There is correlationbetween torque and fluidlossThe lower fluid loss value the lower value oftorque

API Fluid loss decreaseswith addition of CMC(and lubricant)

CAKE0,8


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THICKNESS -

TORQUE

0

1

2

3

4

5

6

7

8


Mud

Torque(Nm)

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

Th

icikness(mm)

60 min Filter cake thickness

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7


Mud

Cakethickness(mm)

30 min

16 sati

Cake thicknessand torquedecreases with

increasingconcentration ofCMC (andlubricant)

The thinner cake the lowertorque

PLASTIC0 03

0,035


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VISCOSITY -YIELD POINT

0

0,005

0,01

0,015

0,02

0,025

0,03


Mud

Plast

icv

iscosi

ty

(Pas)

Plastic viscosityand YP

increase withincreasingconcentrationof CMC (andlubricant)

0

5

10

15

20

25

30


Mud

Yield

Po

int(Pa

)

GEL16,00


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GEL

STRENGHTS -pH VALUE

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00


Mud

Gelstrenght(Pa)

10 sec

10 min

Gel strengthincreases and pH

value decreaseswith increasingconcentration of

CMC (andlubricant)

7,5

8

8,5

9

9,5

10

10,5


Mud

pH


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Cement Sticking

Although cement sticking canresult from a mechanicalmalfunction such as pumpfailure or leak in a string ofpipe, there are three primarycauses:

displacement has beenmiscalculated,

the hole has washed out as aresult of efforts to contain a

downhole blowout, andefforts have been made toprevent excessive lostcirculation.


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Junk in hole,smaller fish, lost in the hole may include:a. bit cones, bearings, or other parts lost when a bit breaks;

b. broken reamer or stabilizer parts;

c. metal fragments lost in a twist off;d. metal fragments produced by milling the top of a fish to aid

in its retrieval;

e. naturally occurring pieces of hard, crystalline, or abrasiveminerals such as iron pyrite;

f. tong pins, wrenches, or other items that fall into the holebecause of rig equipment failure or by accident;

g. equipment such as packer, core barrels, and drill stem test(DST) tools that become lodged downhole; and

h. wireline tools and parted wireline.

Preparing for a fishing job


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When it becomesnecessary to fishdrilling equipmentout of an uncasedhole, one has tofind out as muchas possible about

the situationbefore takingaction.

The questions to answer are:

1. What is to be fished out of the hole?

2. Is the fish stuck, or is it resting freely?

3. If stuck, what is causing it to stick?

4. What is the condition in the hole?

5. What are the size and condition of thefish?

6. Could fishing tools be run inside oroutside the fish?

7. Could other tools be run through thefishing assembly that is to be used?

8. Are there at least two ways to getloose from the fish if it cannot befreed?

Fishing tools


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Fishing, either in openhole or inside casing,involves operation of thefollowing tools andaccessories:1. Spears and overshoots

2. Internal and externalcutters

3. Milling tools

4. Taps and die collars

5. Wash over pipea. Wash over pipe overshot

(releasable)

b. Wash over pipe back-offconnector

c. Wash over pipe drill collarspear

6. Accessoriesa. Bumper jar

b. Mechanical jar

c. Hydraulic jar

d. Jar accelerator

e. Hydraulic pull toolf. Reversing tool

7. Safety joints

8. Junk retrievers

9. Impression blocks


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In a fishing job involving the drill string, theoperator can often ascertain whether or not thelost drill pipe is stuck in the hole by determining

what happened just before it was lost.If the bit was on bottom and drilling, and if there was nosudden, unexplained increase of torque or decrease inrotary speed before the drill string broke, the most likelyexplanation is the occurrence of a twist off and the pipeis probably not stuck.

If the pipe was motionless in the hole or if it was being

raised or lowered but not rotated, it is probably stuck -either mechanically or differentially.

The operator must determine, as accurately as possible,the depth at which the top of a broken drill string can be


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the depth at which the top of a broken drill string can be

found.The upper section of the string is measured as it is removed fromthe hole.

If the bit was on bottom when the drill string broke, or if the drillstring become stuck off bottom, the length of the upper part isthe same as the measured depth of the top of the fish.

If the drill string broke with the bit off bottom and the fishthen fell downhole, the remainder of the drill string in the


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then fell downhole, the remainder of the drill string in the

hole must be measured as it is set back.The depth of the top of the fish can then be closely estimated,assuming that the fish fell all the way to bottom.

If there is any doubt about the fishs location, the operator canrun an electric log.

Freeing


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Flowchart

Locating the fishPi t t h th d O f h ld d


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1. Pipe stretch method One of the oldest andquickest free point methods is the drill pipe stretch test(the method should be used only as a guide, forpreliminary decisions or when the drill string is

plugged);- to run the test, pick up the weight of the drill string and mark

the drill pipe opposite the rotary top,

- pull up additional 100000 to 200000 N (depending on hole

depth) and measure the distance from original mark and therotary top.

FAeEL s

=

L length of free pipe, m

E modulus of elasticity, 211010 Pa

e differential elongation, m

As pipe cross section area, m2

F differential pull, N

Locating the fish


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2. Electrical free-point Surveyshave eliminated most of the guess

work about where to back off andstart fishing;- The free-point detector is lowered

through the drill pipe on an electric lineto locate the lowest point where the

pipe is free.- That is essentially a strain gauge device

to measure molecular rearrangementlocated between drag strings orelectromagnets. Stops are made at

increasing depths, torsion or stretch isapplied to the drill string, and thedegree of pipe movement is measuredat the surface. (Torsional movement ismore important in deviated wells.)

ELECTRIC

CABLE

TOOL JOINT

LOCATOR

FREE-POINT

INDICATOR

COIL

STRING

SHOT

Locating the fish


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- After the free-point detectorpasses the stuck point, no

movement will register whenstrain is applied.

- Free-point devices can be run inconjunction with a string shot to

permit a back-off as the free-point is determined


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Locating the fish3. Drill pipe recovery log The drill pipe

recovery log is an acoustical survey usedto determine stuck points in the drillpipe, collars, casing and tubing.

- The survey is normally run when the fish isextremely long.

- Results are used to evaluate the severity ofthe fishing job prior to undertaking or

sidetracking.

Back-off procedures


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String shot The string shotis a length of prim cordexplosive which is detonatedby an electrical cap.

The shot is run into the well tothe desired depth opposite atubing coupling or tool joint asindicated by the collar locator at

the top of the assembly.Back-off is completed byapplying left-hand torque to thestring and holding while the shotis exploded.

If the correct torque is applied,the jar of the explosion willcause the threaded connectionto unscrew.

Making a cut


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Electric line cutters areused where conditionsprevent backing off at the

required depth.Two basic types of cutters areavailable: jet cutters andchemical cutters.

Jet cutters This cuttersuse a high velocity beam ofgases created by the shapecharge to cut the pipe.

Making a cut


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Hydraulic pipe cutters -can be:

erosional (A) or

mechanical cutters(B)Erosional perforators enablelimited penetration in to theformation with greatdifferences in opening shapeand penetration depth.

Their use is limited becausethey are long-lasting andexpensive.

Mechanical cutters cutsection of the pipecompletely.

They are also limitedaccording penetration andlast long.

(A) (B)

Making a cut


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Chemical cutters Thechemical cutter uses astrong acid to make the cut.

Oxidation destroys the pipe.

When this cutter is used, acidconcentrations and quantityare designed so that the acidis completely consumed in the

cutting process.Both cutters perform thesame function, butchemical cutter gives a

smoother cut.

Making a cutMechanical cutters can be internal


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Mechanical cutters can be internaland external.

Internal hydraulic (mechanical) pipe cutteris used to cut single or multiple strings ofcasing in one or more runs.

The tool consists of a:top sub,

a body, a piston, a piston spring, a flowindicating device and

cutter arms.Upon pumping fluid through the tool, apressure drop is created across the pistonforcing it downwards.

The lower end of the piston stem pushes onlugs at the upper end of the arms, makingthem pivot and forcing their lower tips intocontact with the casing.

The hard metal with which the arms have

been dressed cuts the casing.

Making a cutThe section mill is a hydraulically actuated tool


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The section mill is a hydraulically actuated toolused to mill a section or window in casing ortubing.

It can also be used as a pipe cutter.The tool consists of a top sub, a body, a piston with cam, apiston spring, a flow indicating device, cutter knives andarm stop stabilizers.

Upon circulating through the tool a pressure drop iscreated across the piston which forces the cam down the

ramp of the knives, welding them into contact with thecasing.

Half the number of knives part the casing and all theknives participate in the subsequent milling effort.

Lower standpipe pressure indicates that the pipe has

been cut.When circulation is stopped the piston spring will lift thepiston, making the cam withdraw from between theknives, and they will collapse into the body.

Internal mechanical pipe cutter


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is used to cut strings of tubing, casingor drill pipe; particularly useful incutting small diameter strings.

By rotating the mandrel and cutterassembly clockwise relative to otherassemblies the slips move axially due to ascrew drive between the lower end of themandrel and the friction assembly.

This forces the slip segments to expand,

traveling up on a cone.Once the slips are set, weight can beapplied, causing wedges to force cuttersinto contact with the pipe.

The screw drive thread of the friction blockassembly is cut on spring loadedsegments, and to disengage the knivesand slips and to reset the tool for anothercut it is only necessary to elevate the

string.

External mechanical pipe cutter isemployed in cutting tubular strings from theoutside.


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It is used to externally cut and retrieve drill pipeor tubing, regardless of the tool joint.

The tool consists of a top sub, a body, a pistonassembly, knives and a guide.

The piston assembly consists of a rubber ring, conicalpiston segments and a feed ring.

The piston segments are kept together by the rubberring and each has a hole drilled through it.

These holes are sized to permit circulation through the

tool as well as providing adequate pressure drop tomake it function.

When running in the hole the piston assembly is kept inthe up position by two shear pins..

Upon kicking in the pumps and building pressure, the

pins shear, permitting the feed ring to wedge in behindthe knives, thereby forcing them into contact with thepipe to be cut.

A secondary way of actuating the knives is to raise thestring until the piston segments engage below a

connection and then pull 4500 N tension on the string in

The condition of the fish


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Hole conditions, inparticular whethercirculation can bemaintained, are importantconsiderations inrecovering a fish.

If drill pipe is stuck by acave-in or by swelling shale

circulation my be restrictedor cut off altogether.

However, circulation isusually not affected if thedrill string is stuck in a keyseat or if pipe is wall stuck.

The condition of the fishalso is essentialinformation.

Most pipe recovery tools aredesigned with close

tolerances; that if specificcomponent sizes areneeded for specific jobs.

Irregularities likely to

hamper recovery of a fishmust be dealt with.For example, if the top of asection of broken-off drillpipe is burred or split, it

may be necessary to cleanup, or dress, the pipebefore trying to retrieve it.

And junk may have to bebroken apart so that it canbe picked up.

Inspecting the break on the part of the pipe

Impression block


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that is pulled from the hole may provide agood reverse image of the top of a twist off.

One method that is sometimes used toassess the condition of the top of a fish is torun an impression block.

A typical impression block consists of a block oflead, having a circulation port, molded onto a steelbody.

The block is made up on drill pipe and collars andrun into the hole until it is just above the fish.

Circulation is started to wash all settlings off the topof the fish so that a good impression can beobtained.

The block is lowered gently to touch the fish, andweight is then applied.

The top of the fish indents the bottom of the softlead block, leaving an impression that can beexamined and measured at the surface.

Mills


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If a part of drill string hasbroken off in open hole andit is not stuck, the fishing jobconsists mainly of locating

and engaging the top of thefish with an appropriate tool.

If the top of the broken-offpipe is badly split or twisted,

it requires that the damagedmetal is removed to give afish a more acceptableshape, because most fishing

techniques require a sectionof straight undamaged pipeto make a firm catch.

During milling, the drill string


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g g, gmust be rotated quickly andcarefully.

It may be necessary to use apilot mill, which will not jumpoff the top of a fish and go

down beside it.High-volume circulation shouldbe maintained to flush thecuttings and cool the mill.

A ditch magnet can be placed inthe return line between theshale shaker screen and themud pit to capture mostcuttings from the millingoperation.

Removal of cuttings reduces

wear on mud pumps and otherequipment.

A typical fishing

Fishing assembly


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string consists of,from bottom to top:

an overshot,

a bumper sub,

a hydraulic jar,

a series of drill

collars,and a jar acceleratormade up on drill

pipe.


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It is recommendedto install the safetyjoint as the part of

the fishing string.Because whenengaged, and the

jarring does not freethe fish, the safetyjoint can be broken

out by rotating tothe left and loweringthe drill string.

External catchDie collars are used toexternally engage and retrieve


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toolsa tubular fish.The fish must offer somerotational constraint as thegripping force depends upon theamount of torque with which the

die collar can be made up to thefish.

Its bor permits the passage of wireline tools

The tool is a solid one-piececonstruction conical cylinderfurnished with a fine casehardened thread on its inner

circumference.Upon being screwed over the fishthe hardened threads embed inthe softer material of the fishsecuring a good grip for retrieval.

OvershotA typical circulating and


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releasing overshotconsists of three outsideparts:

a top sub,

a bowl, anda guide.

The top sub connects theovershot to the fishing

string.The bowl may be fittedwith different types ofequipment to grasp the

fish and different guides tohelp center the fishbeneath the tool.

TOP SUB

BOWL

BASKET

GRAPPLE

FISH

GUIDE

Two kinds of grapplesare possible:

i l l


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spiral grapple;if the diameter of thefish is close to themaximum catch size forthe overshot, and

backet grapple;if the fish diameter is

below the maximumcatch size.

Both types of packersseal around the fish,allowing drilling fluid tobe pumped down toclean out the bottom ofthe hole.

The fishing string is run to


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within a few feet of the topof the fish.

Circulation starts to cleancuttings and settlings off thetop of the fish and to clean

out mud cake from inside theovershot.

The fishing string is slowly

lowered to touch the top ofthe fish and establishes itsexact depth.

When the fish has beent d h k l d


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tagged, hook loaddecreases;

the position is marked on thekelly.the string is raised, and, withslow rotation to the right,lowered slowly withoutcirculation,

if the overshot is centeredover the fish, the loweringand right-hand rotation ofthe string forces the grapple

upward within the taperedhelix of the bowl, allowingthe grapple to expand andthe fish to enter theovershot.

After the string has been lowered, the

i ht i di t h ld i t d


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weight indicator should register a decrease.When the fish is engaged, rotation isstopped and all torque of the string relieved.

Than upward strain is taken.This causes the fish to pull the grappledownward and the wickers on the grapple to

bite into the fish.If the fish is gripped tightly, the weight indicatorwill show an increase.

Circulation is started, without rotation, to cleanout the hole before the fish is brought to thesurface.


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If it is not possible to pull out the string itmust be stacked.

To break out a string from the fish, theovershot is bumped down and rotated tothe right and gradually raised until it isclear of the fish.

When coming out of the hole with the fishengaged in the overshot, the procedure isthe same, but the rotary slips in rotary

table are used and the overshot is bumpedon them.


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If the upper end of thefish cannot be engaged,

an extension sub isinstalled between the topsub and the bowl of the

overshot to allow thedamaged top of the fishto go past the grapple.


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Different guides can

be used.If the top of the fishis in a washed-out

section of the hole,a wall-hook guidemay be used in

place of the regularguide.

When a wall-hook guideis used, thedistance from the bottom of the guide tothe top of the wall-hook opening and

from there to the stop in the overshot ared


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from there to the stop in the overshot aremeasured.The string is run in to a point just above thefish, then lowered with slow rotation until theguide tags the fish.

Downward movement is then stopped, butrotation is continued.

Torquing up of the fishing string is a sign thatthe fish is caught in the wall-hook opening.

The rotary table is locked and the fishingstring is raised.

A release of torque signals that the top of thefish has slipped beneath the top of the wall-

hook opening and is centered beneath theovershot.

To engage the fish previously definedmeasures are taken.

FISH

OVERSHOT

GUIDE


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In a very large

washout, a knucklejointmay be madeup above the

overshot to extendthe wall hook andovershot out into

the cavity.

WALL

HOOK

OVERSHOT

KNUCKLE

JOINT

Inside fishing

toolsWhen a drill collar separates, the

break usually occurs at a


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toolsbreak usually occurs at aconnection ; thee pin breaks offin the box, or the box breaks offand comes out with the top part

of the string.If the diameter of the drill collaris very close to that of thewellbore (as in packed holeassembly), an overshot may nothave enough clearance to goover the collars.Either a fishing neck must bemilled on the top drill collar or an

inside fishing tool must be used.The simplest inside fishing tool isthe taper tap(without or withguide).

The tap is lowered into the collar boreand slowly rotated to make its ownthreads as it engages the fish.

The taper tap is no releasing, and it is used


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The taper tap is no releasing, and it is usedonly when a releasing tool cannot be run.Some taps have open tips, allowing limitedcirculation for cleaning off the top of thefish; others have small side jets that movethe point of the taper tap to help locate thetop of the fish.

Once the tap is made up in the fish, thepump pressure and torque increase, and

the fishing string and fish are trippedout.The taper tap should always be run with asafety joint and jar, because once a tap isengaged it cannot be backed out of a stuck

collar.If jarring does not free the fish, the safetyjoint can be broken out by rotating to theleft and lowering the drill string.

The most common inside fishingtool is the releasing spear


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tool is the releasing spear.

The spear is made up on the fishstring and lowered, withcirculation, to the top of the fish.

Circulation is then stopped, and

the spear is lowered slowly insidethe fish until the weight indicatorshows a decrease, indicating thatthe bumper ring or stop sub hasseated on top of the fish.

Rotate sufficiently to move the mandrel

one full turn to the left.


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one full turn to the left.This turns the mandrel down through thegrapple, placing the grapple into engagingposition.

A straight pull will then wedge the grappleinto positive engagement with the fish

The spear is made up on the fish stringand lowered, with circulation, to the top

of the fish.Circulation is then stopped, and thespear is lowered slowly inside the fishuntil the weight indicator shows a

decrease, indicating that the bumperring or stop sub has seated on top of thefish.

To release:

Bump down to break the freeze then


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Bump down to break the freeze, thenrotate two or three turns to the right.

This moves the mandrel up through

the grapple, forcing the grappleagainst the release ring and puttingthe spear in released position.

A straight upward pull will thengenerally free the spear, however, itis recommended that the spear berotated slowly to the right when

coming out.

Stop sub is used to locatethe top of the fish when

stop is required. It isi ll d i h b


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stop s equ ed t sinstalled in the boxconnection at the top ofthe mandrel.

Oversize stop ring isused with stop sub whenuse of larger stop isrequired. It is installed on

the stop sub with set ofscrews.

Mill type nut is used tomill away burrs from thetop of fish.

Side hill type nut is

used to center thei tl i


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spear in greatly oversizeholes to assure entry ofthe spear into the fish.

Pack off assembliesareused to pack-off all

sizes of tubing, drill pipeand casing.

The assembly is attachedto the sub type nut

below the spear where itpacks-off the fish inorder to circulate throughthe fish.

Fishing of stuck pipe

After a fish has been caught in the


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After a fish has been caught in theovershot, the usual procedure is tocirculate out the settled cuttings

without rotation.If circulation cannot be fullyestablished and the fish cannot be

pulled, the fish is almost certainlystuck mechanically in the hole; in suchcases thejarmust be used.

Jarscan be mechanical or hydraulic.

The simplest is a bumper jar.That is a device that permits vertical

t f th ti ith t


104/123

movement of the upper section withoutmovement of the lower section of thetool within a limiting travel; usually about

0,5 m.Raising the upper section with theworking string to the limit of travelwill produce a slight upward jar on

the lower section.Dropping the string quickly willproduce a sharp downward jar orbump on the lower part.

The jarring blow will be morepronounced if a few drill collars areplaced in the string just above thebumper jar.


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Mechanical jarThe force of the mechanicaljar depends on the amountof torque turned against thetrip mechanism.

The greater the torque, theharder the jarring blow when

the tool trips.

Hydraulic jar depends for its intensity upon

the pull taken on the tool before it trips.l d d l b l h d ll ll h


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It is placed directly below the drill collars in thefishing string.

The intensity of each blow is controlled by the

amount of stretch placed in the drill string.The more pull, the harder the blow.

The jarring effect is enhanced by placement of drillcollars above the jar.

The hydraulic jar enables only upward jarring,so if there is a need for downward jarringcombine it with mechanical jar.

To activate the oil jar, pull to a predetermined

distance above the weight of the string at thejar.

Hold this position while the oil jar bleeds offand the blow is delivered.

Jar, surface bumperis designed to beinstalled in the drill string at the surface.

It permits the operator to deliver sharpdescending impact or downward jarring


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descending impact or downward jarringblows against fish at its stuck point.

At last 1300 to 1800 N weight must beinstalled on top of the jar in order to be ableto reset the tool by closing it.Upon extending the tool from its closedposition the friction mandrel pulls the frictionslip into the upper (narrow) part of the bowluntil the slip stops against the control ring.

The control ring is threaded and translatesaxially upon being rotated.Its position determines how far into thetapered bowl the slip is allowed to travel andconsequently the tripping load.

When the preset load is exceeded the jaropens, permitting the drill string to drop thelength of 1,22 m stroke.

The Intensifieris

essentially a fluid springwhich stores energy when ai i ll d h


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strain is pulled on therunning string.

When the strain is removed

by the free stroke of the jar,the stored energy isreleased, accelerating thedrill collars and jar endupward until a blow of high

impact is struck.Its function is to supplyacceleration to the upperend of the jar and lower

portion of the work stringduring the jarring stroke.

Circulating fluid through thewash over assembly flushes

out sand or shale in the spaceoutside the fish


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outside the fish.

The wash over drill collar spearis used in conjunction with awash over string to engage and

retrieve a fish which hasbecome stuck off bottom.The spear is connected to the fishbefore the wash over operationstarts and will engage in the wash

over pipe if the fish drops free,thereby preventing it from fallingto the bottom of the well.

Fishing for junkOne of the simplest rotary

fishing tools is the junkbasket.


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basket.It is run into the hole on thebottom of the drill string to

within a meter of the bottom,then lowered over the junkwhile being slowly rotated.

If the basket is nearly holesize, its finger link catchers

will gather junk toward thecenter of the hole, and whenweight is applied, bendinward to trap the junkinside.

Most effective for a small,solid mass lying loose onbottom, such as a bit cone.

The core-type junk basketis used toretrieve junk such as cones that may or

may not be embedded in the formation.A mill shoe is made up on the bottom ofth t l


111/123

the tool.After it is run nearly to bottom, mud iscirculated at reduced pressure, and thetool is slowly rotated and lowered to touch

the junk.Weight is gradually increased.The mill shoe cuts away the protrudingedges of the junk, as well as theformation, forcing the junk and a shortcore into the barrel.

Rotation and circulation are stopped,torque is released from the drill string, andan upward strain is taken to break off thecore.Upper and lower catchers in the baskethold the core and junk on the trip out.

A magnet insert can be used in the tool topick up small pieces of ferrous metal

A boot basket, also called a junk subor junk boot, may be run just abovethe bit during routine drilling to collectsmall pieces of junk that may damage


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small pieces of junk that may damagethe bit or interfere with its operation.

Usually a but basket is run above amill while it is milling away a metallicobject such as the top of a fish.

During drilling or milling with circulation,the mud flowing upward in the narrowspace between the boot basket cup andthe hole wall flows rapidly enough to carrypieces of junk with it.

When it reaches the annulus above the

cup, however, it slows down, and thelarger bits of junk drop out into the cup, tobe retrieved when the bit or mill is pulled.

CUP

Ferrous metallic junk can often be retrievedusing a fishing magnet, a powerfulpermanent magnet having passageways forcirculation.


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A fishing magnet is lowered into the hole witcirculation to wash cuttings off the top of thejunk.The magnet is encased on the top and sidesby a nonmagnetic brass sleeve to preventjunk from clinging to the side of the magnet.A skirt on the bottom of the magnet keeps thejunk from being knocked off during the tripout.If there is no fill on top of the fish, magnets

can also be run on wireline, a much fasteroperation than tripping, the drill string in andout.

HOOK GUIDE

MILL GUIDE

WIRELINE

CONNECTOR

SidetrackingSome fishing jobs

can go on formonths before thefi h i t i d


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fish is retrieved.Than the

sidetracking couldbe the option.Knowing the rateof penetration andthe length of theoriginal hole tobypass, one canestimate the costof drilling new hole

to reach theoriginal tool depth.

Packer milling and retrieving tool

The tool is used to retrieve all typesf f ll b d ti k


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of full bore production packers.

The tool consists of a:

canfield type drive bushing

a long wash over show with

a wash over pipe extension, and

a packer retriever spear with threadedextension rods between it and the canfieldbushing.

Packer milling and retrieving tool

The tool is assembled andconnected to the runningstring lower into the hole and


116/123

string, lower into the hole, andspear carefully run throughpacker.

By having run the spear throughthe packer the slip has beenautomatically set in the catchposition by friction contactbetween it and packer bore:

Verify by picking weight;Lower, establish circulation andstart milling the packer;

When the slips and the sealingelement have been milled away,

stop rotation and elevate thefishing string to engage andretrieve the packer.

Wireline fishing

One of the most challenging of allfishing jobs is the recovery of wireline


117/123

g j yand the tool or instrument run with it.

The first consideration is whether theline is parted or is still intact.

If a conductor line has not parted, it is

good practice to avoid pulling it out of therope socket.

If this occurs, contact with the tool or

instrument will be lost, possiblypermanently

Wireline fishing

To fish intact wireline, either the:cable-guide method or


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cab e gu de et od o

the side-door overshot method can be

used.The cable-guide method should bechosen for all deep, open-hole

situations or when a radioactiveinstrument is stuck in the hole.

This is the safest method and offers a

high probability of success.

Cable-guide fishing

The tools consist of:a cable clamp with a T-bar,

rope sockets for each end of the


119/123

rope sockets for each end of theline,

one or more sinker bars,

a special quick-connector-typeovershot for the line on thereeled,

and a spear point for the well

end.Also included is a slotted plateto set on top of the pipe, a subwith a recess or retainer to

hold the rope socket and anovershot to run on the pipe tocatch the instrument or toolstuck in the wellbore.

Side-door overshot method

The side-door overshot is aspecial overshot with a gate ord i th id th t b


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door in the side that can beremoved to allow the line to be

feed into the tool, after which thedoor is put back into position aspart of the bowl.

The overshot is run on drill pipe ortubing until the fish neck or bodyof the stuck tool is engaged.

The advantage of this recoverymethod is that the line does notneed to be cut.

Fishing parted wirelineThe Rope Spear is a reliable and efficient wireline andwire rope retrieval tool.

The rope spear retrieves all sizes of electric wireline, slickline, braided line, or other types of wire rope that havebeen left downhole


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been left downhole.It can also be used to retrieve control line or ESP cablethat has been left downhole.This tool has been very successful in recovering theseitems in cased or open hole.The Rope Spear is one of the easiest tools in the industryto operate.

The tool is dressed with the proper lower shank, rundownhole on two or three drill collars to the requireddepth, and rotated to the right until ample contact withthe wireline is achieved.As the work string is pulled up, the wireline that iswrapped around the spear slips down and latches ontothe barbs.Assuming satisfactory contact is made with the wireline,the retrieval operation can be successfully completed inone run.

Fishing parted wirelineThe Latch Jack is a wireline fishing tool

designed for fishing wire throughrestrictions or wire that has become


122/123

balled up.

The tool is manufactured from high tensilesteel so that the prongs may be forced downinto or around a reasonably compacted ballof wire.

The design incorporates barbs on the ID onlyso that wire on the outside of the tool maybe easily pulled down rather then having toyield the wire creating smaller unfishable

pieces.Similar spears are manufactured withoutthe latch in two and three prong designs.

Cutting the lineThe Mechanical Wireline Cutter is used to cut a

wireline just above the rope socket of a stuck tool.This allows the cut line to be retrieved in one piece whileproviding a desirable fishing top on the stuck tool.


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providing a desirable fishing top on the stuck tool.The cutter is installed over the line and run in on wirelineor pipe, if clearances permit.

The cutter is installed over the wireline by removing thekeeper block.The keeper block is replaced and the cutter attached to arun-in line by means of a rope socket or crossover sub.Cutting knives are then activated by applying an upwardstrain on the run-in line or pipe that continues until the cutis indicated.The cut wireline and run-in line (or pipe) are then retrievedand fishing operations begun on the stuck tool.

It may be desirable, when line condition isquestionable, to make a dummy run with cutterknives removed to be certain that no obstacles areencountered from surface down to the stuck tool.

15 drilling instrumentation

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