primary and remedial cementing

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PRIIvTARY ND REMEDIALCEMENTING



I.

u.

PRIIVIARYAND REMEDIALCEMENTING

TABLEOF CONTENTS

INTRODUCTION

CEMENTCI{EMISTRYAND TESTING

A. N,IANUFACTURINGAND RESULTINGCOMPOUNDS

B. API CEMENTCI-ASSES

C. SETTINGOFCEMENT

D. CEMENTTESTING

E. CEMENTSLURRYDESIGN

PRIMARY CEMENTING

A. INTRODUCTION

B. FUNCTIONS

C. SUBSUMACE EQUIPMENT

D. SURFACECEMENTINGEQI.IIPMENT

E. PRIIVIARYCEMENTINGPROCEDURESO

ENI{ANCE SUCCESS

F. POSTJOBCONSIDERATIONS

G. SPECI,ALOPERATIONS

H. CEMENTEVALUATION

I. ANNUI-AR GASFLOWIflTIGATION

REMEDIALCEMENTING

A. PLUGCEMENTING

B. SQIJEEZECEMENTING

PAGE

1

I

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3

8

20

3 l

3 1

31

32

36

M

56

56

63

66

72

73

86

99

103

m.

IV.

LIST OFREFERENCES

APPENDD(A



I .

II .

PRMARY AND REMEDIALCEMENTTNG

INTRODUCTION

Thepurpose f anoil or gaswell cementob is to placecement lurryand/or ementilter

cake n apredetemrinedocationdownhole.After beingplaced,he cement etschemically

by aprocess f hydration;his resultsn the developmentf mechanical trength nd he

establishment f a hydraulicseal. In almostall instancesheseoperationsareperformed

usinga slurryof Ponland-type ementn water. This coursewill cover heformulationof

and echniquesor the effectiveuseof theseype slurries.

CEMENTCHEMISTRYAND'IESTING

ManufacturingndResultingComlnunds

Portland Cementsare still manufactured singmaterialsandmethodssimilar to

thosedeveloped y JosephAspdin in 1824. Groundcalcareousock (CaCOs

source)andgroundargillaceousock (aluminosilicatesource), longwith some

iron ore, areburnedn a kiln at high temperailre. The resultingclinker s then

intergroundwith gypsum o form Portlandcement.This processs depictedn

Figure 1 after Reference1**. Resulting rom this operation s a mixture of

anhydrousxidccompoundssshownn Table .

A list of rcferencess foundat theendof thissection.

Figure I

Manufacture f PortlandCement

(AfterReference)

A.



Comoound

TricatciumSilicate 50Vo

B-dicatcium ilicate 257o

Tricalcit'maluminate l0Vo

Tetracalciumluminoferrite l0Vo

Otheroxides SVo

TABLEI

COMPOSMONOFTYPICALPORTI-ANDCEMENT

Approximate

Concentration Formula

3 CaO.SiO2

2 CaO.SiO2

3 CaOAl2O3

4 CaO.AlzC:.FezQ

Abbreviated

Desienation

CIS

CzS

clA

C4AF

C3Ss a fast-rcacting omponentwhich rccountsor early-timestrength evelopmentn the

setcemenl

C2S s a slower eactingcomponenthat is responsibleor the long term strengthand

durabiliry n the setcemenl

C3A is the fastest eactingcomponent, nd n its hydratedorm is sensitive o sulfate

waters.

C4AF s nothighlyreactiveanddevelops ery ittle exotherm n setting.An important oleplayedby thiscomponents to control he concentrationf C3A n the inal product.By

incorporatingmore ron ore(FezQ) in thekiln fee4 theproductionof C4AF s favoredat

theexpensef ClA.

B. API Cement lasses

APISpecif icat ionl0(Reference2)l iss*(A,B,c,D,E,F,G,

H andJ). Ofthese,D, E, F, andJ arevery seldom,f ever,encountered. or oii

andgaswell applications,

It canbeseenromTable2.1(cheinicalcquircments)n API Specification 0 hat

theAPI specifications more cstrictivewith regardo composition f ClassG and

H cementshan for ClassA. Also, Table2.2 (PhysicalRequirements)n

2



c.

Specification10 ndicates hat the performance ests or API ClassG andH cements

are conductedat higher temperarures han for ClassA, and ffi

ClassA cements available nly asOrdinaryType(O) whercasClassG andH are

availableasModerateSulfate-ResistantYPE (MSR)or High Sulfate-ResistantType (HSR). FromTable2.L, t can be seen hat ClassA (O), MSR andHSR

q'pesdiffer in that hc C3Acontentof ClassA (O) is uncontrolledand or theother

t1ryeshe C3Acontents limited o 8 percentmar( MSR)or 3percentmal( HSR)'

Actually, thc dclcterious ffectof thc dissolvedSO4-zon on hydratedC3A s most

pronouncedn the 80-100'F temperatureange; t hasvirnrallyno effectat 100-

180'F andno effectabove180'F. Therefore,n mostoil-field applications,he

choicebenveen n O, MSR,or HSR ypeof cements based nconsiderations,ot

of sulfateattack, uton costand eactivity,.e.,ease f retardation.Thehigher he

concentrationf C:A, thegrcatcr he cactiviry.

Settine f C-€ment

l. HydrationReactions

In a cement lurrymixedat thecorrectwater o cementatio,approximately

nro-thirdsof the totalwater s required o wet the cementgrains,and eact

with thecemento forrr an narlocking hydratestructurc.The development

of thc hydratestnrcnrres shownby a scanningelectronmicrographas

Figrrrc2 (Refer€nce ).

i On filteringa cement lurry, t is this

one-thirdof mix water hat s lost to theformation, .e.,duringa squeeze

job in the field, or to the graduate ylinder(doinga fluid losstest n the

laboratory).The othernvo-thirdsof themix water emainsn thefilter cake

asoneof componentsf thecementhydratestnrctueandasa smailamount

of interstitialwater. It is for thisreasonhatUseof thecorrcctwater o solids

ratio is avery mportantslurrydesignparameter.The useof greaterhan

designamountsof mix waterwill result n excessiveree water, solids'

settlingand nferiorsetpropertiesn the cement. fi



Figure

PASTES OF PORTLAT{D CE}IENT appcrr b scenning .lcctroo

microgrephr madc et vrriorr stegcl ol hydndoq tbrt i$ at vriour

timcr aftcr nrtct r.r mircd wltb thr ccDG!! Aftcrtwo hour: (/) tbc

initirl gcl cortingl erc visiblc around thc ccmcnt grains' After a mc'rA

(Z) ttifit.ift rr- cvidcnt' as rrc largc Phtalike csysbls of cdc'-'r

iydrorida Dcteil of srnc samplc (J) shows thc iotcrlocking fibars'

4

,



A chemical equationcan be used to depict the complete hydration of

tricalcium silicate(Ref4):

2 (3CaO.SiOd 6H2O= 3 CaO.2SiO2.3H2O3Ca(OH)z

Simitarchemicalequationsambewfittenfor the othercement omponents

shownn Table . Thereare several oints o bemade rom a consideration

of the aboveequation.

Cement ets,.e. develops trength nd mpermeability, sa result

of hydration, ot asaresultof dehydration, r "dryingout" as t is

sometimestated.

As indicatedby the abovechemicalequation,Ca(OH)zs a byproductof the cementhydrationeaction.Because f this,cement

slurry,cement iltrate,and he setcementare all alkaline pH of

12.U12.4).The high pH of the primarycementsheath reates

passiveilm on the steelcasing,.e.protectst from corrosion.

Another byproductof the hydration eaction(not shownby the

aboveequation)s heat"or to state t differentlythe hydrationof

cements exothermic.Reference (on p.29$ givesthe heatof

hydrationof a neatcementmixed with 40Vowater(by weight of

cementor bwc)as 61 caVgram.Thc effectof this exothermon the

temperaturef awell cements shownby Figurc3.

Cement-topemperanre urveys re based n thiscementproperty. It is

evidentfrom Figure 3 that thetemperaturemaximum s attainedat some

particular ime aftercementing;or mostprimarycementobs the optimum

timeto run a cement-topemp€ranr€ urveys Gl2 hoursafter bumpinghe

plug. For a typical cement-toPemperanresurYeyseeFigure 4; the

undisturbed eothemral radient s shownasa dotted ine.

Effectsof Temperaturc.essureandSurface rea grind)

Temperature: The rate of most chemical reactions is acceleratedby an

increasen temperature; his general rule also applies to thc hydration of

)



Figurc 3

h i c i r t o i h r d r l r t i on I t r r t ' l u r d i l l c run t 11 l l 5 ' rc l l

deorh. oo t1. 1)

6



Figure4

TypicalTemperatureurveyAfter Cementing

9 0 ' F l o o o F 1 1 d F 1 2 0 0 F

PROBABLEC E M E N T T O P

1 0 0 '

1400 '



D.

cement. A measure f the rate of reactionof cementwith water s the

thickening imeof the cement lurry. Thethickeningime of a cement lurry

is definedas he engthof time hatacement lurrywill remainsufficiently

fluid to be pumped,when testedundersimulateddownholeconditions.

Reductionn thickening ime s indicativeof afaster eaction ate. Thedata

of Figure5 showa reductionn thickeningime, .e.,an accelerationn rate

of reaction,with increasesn temperanrreor four differentcement lurries.

Pressure: Increasesn confining pressurealso have the effect of

acceleratingherate of thehydration cactionanddecreasinghethickening

time. This effect is illustrated or a cementslurry testedat a constant

temperature200'F) by the dataof Figure6.

SurfaeArea: A cementhat s gfoundmore inely has elativelygreater

sgrface rcaand herefore asmorcareaavailableor thehydration eaction.

lI|tFF The effectof grind is illustratedby the dataof Figure7,

which was taken rom Reference . Predictably,as the finenessof the

cementncreasedshownasgreater urfaceueaper unit of weight), he

thickeningimewasobservedodecrease.

Cernent esting

A cement lgrry or anyoiVgaswell applications designed y fint consideringhe

purposes f the cementob and thc environmentnto which the slurry will be

placed.A cement lurry s preparedn the aboratory sing hespecifiedwater o

solids atio and bestguessas to requiredadditives ype andconcentration; he

slurry s then esredo determinets suitability or the ntendedapplication,and

changesn composition remade,f needed. n otherwords,cement esting s a

key pan of the terativeprocess f slurrydesign.Also,cementof the sameAPI

Classwill showsomedifferencesn properties tween differentmanufacnrrersnd

lot to lot differcncesrom the sameunufacnrrccthisvariationnecessitatesrequent

testing.The bestsinglesource f informationconcerningwell cement esting s

API Spec10. In theparagraphshich ollow the estshavingparticularelevance

to thedesign f field cernentinglurries rediscussed



Figure5

Effect of TemperaturcnThickeningTime of Various

API CementstAmpspheric essure 1)

2 4 6 8 1 O

THICKENING TIME, HOURS

200

1 8 0

1 6 0

1 4 0

f izo

trJ

5 100

UJ9 8 0z,t!F

60

40

9

(^1c r A s sMt I I I

c t A s sc t M t i l T

\

c t A s sGc lMt i lT

\

\

\)

c r .AssC€Mt lT + 2X CoC

I >



5 0 0

Figure6

Effect of Pressure nPumpabilityof Cement.

(Cement API ClassH with 0.3Percent etardeq

Bottom-Hole irculating emperature200'F) (1)

0 - 5 0 0 0 1 0 . 0 0 0 1 5 , 0 0 0 2 o . 0 o o 2 5 . 0 0 0 t o . o o o 3 5 . 0 0 0

PRESSURE,Ti

Q't

:! 100

z=

q 1 0 0=

z, 20 0

=-::F 1 0 0

\

1 0



Figure7

LinearRegrcssionf ThickeningTime andBlaine

Finenessor ClassA, G and11gsmsnls 5)

160

1 4 0,7

; 120

i:o 100' -

o

! 8 0

rn 60-coa

40

201 8 0 200 220 240 260 280 300 320 340 360 380

BlaineFinenessmz/kg)

1 l

A =

o -f =t -

Supp l ie rSupp l ie rSupp l ie rSuppl ier, thersLeastSquares

N

R 2

se

Y '

240.928.94294.0 - 0.72x

I/

A A/

A

\-



l . Determinationf FreeWaterContent f Slurry Section of API Spec10

This s a specificuionest or ClassG andH cements,ut t is alsoaneasily

perforrred est that is very useful or slurry designpurposes. This test

providesrvodatapoints: he slurryconsistencyn ABc after2Aminutes fstirring n anatmosphericressureonsistometert 80'F, and hevolume

of free wateroccurringafter the slurry standsquiescentor two hours.

Suitable riteria or mostcementinglurries rea 20-minute onsistencyf

1l ABc + 2 ABc and recwater< 2.5 ml.

OlpratingFreeWaterTest AplrendixM of API Spec10

Forsomecasingcementing pplicationst is required hat hecementslurry

developitde or no freewater.Two suchcritical applications redeviated

wells andwells thatpenetrate as-bearingntervals. The preferredree

water est or suchwells s the onedescribedn AppendixM of Spec.10.

This test nvolvesplacing heslurry n a FITAIPconsistometernd aising

the slurry temperatureo simulatedbottomhole circulating emperature

(BHCT) and simulatedbottomhole pressureBHP) according o an

appropnatehickeningime scheduleTableE.6,8.7, or E.8A n Spec.10).

After ma:rimum emperaturendpressureonditionsareattained,heslurry

is allowed o cool o 194'F (90' C), f necessary,o t canbe ransfenedo

a graduatedylinderandallowed o standquiescentor two hoursat room

temperaturcndatmosphcric ressure.Thevolumeof freewater s then

measurcd.

Thickening imeTests Section andAppendixE of API Spec10

Thickening ime testsproduce ataas o the engthof time acementwill

remain suffrciently fluid to be pumped,when tested under simulateddownholeconditions.API Spec0 describeshe equipment ndprocedures

for performing thickening time tests and, also provides

time/pressure/tempetanuecheduleso befollowed during he hickening

time csts.Theapplicationsf thevarious estschedulesresummarizedn

Table r bclow:

2.

3 .

t 2



TABLE r

APITHICKENING IME SCHEDULES

Application

Specification esting

CasingCementing

LinerCe,menting

Squeeze ementing**

HesitationSqueeze

Tablen Spec.0

8.3

E.6

8.7

E.8A

E.8B

Pagesn

Spec10,3rdEd

27-29

52-57

58-61

62-&

65-70

** also,o beusedorplug-back ementing.

A casing-cementingr liner-cementing ell simulationest(TableE.6 or

E.7 n Spec10) or a givenwell is selected n the basisof thewell depth

and thetemperature radient.The temperanrre radient as F/100 feet of

depthor'(/100 m depth) s based n a "bottomhole static emperature"

(BHST)asdescribednpage5l of Spcc10,and hemeasuredepth MD)

of the well. In somehighly deviatedwells the resulting emperature

gradientwill be lower thanany found in Table8.6 or E.7 (below0.9"

F/100)anda customhickeningime schedule ill be equired.Generally,

theAPI thickening ime schedules re accurate;heyarepredictiveof how

slunieswill perform n mostwells. The API thickening ime schedules ill

not be as suitedto wells with an unusualcircumstance.Examplesof"unusualcircumstances"ncludeoffshorewellswith longrisers in water

depths> 500 feet),wells that penetrate ermafrost, igh anglewells

(discussedbove)andwellswith temperanne radients utside herangeof

Tables .6 and8.7 (0.9-1.9F/100feet). Suchwellswill require ustom

thickening ime schedules;he nput for suchschedulesan betemperanre

mcas'urcmentsnd/orcomputer imulations.

The design hickening ime required or a field slurry is given by the

followingword equation:

thickeningime= surfaceime** + anticipatedob time+ safetyactor

** the cement tartseactingas soonas t is mixed

1 3



4 .

Usualsafetyactor or casing ementingobs s 50Vo f the anticipatedob

time; ocalexperiencemay dictate heneed or moreor lesssafetyactor.

One hundredpercent s commonlyused as a safety actor for liner

cementing perations.Cement lurriesor cementplugoperations o notrequirea large safety actor becausehe placement f a cementplug is

straightforwardand there are reasons see ChapterIV-A) why long

thickening times are undesirable. Longer- time safety factors are

c -' :-' 'h ' ":-' ' ' illll I l' tlll l! tlJlfl t !t I lt ll!

. Therearepotentialhazardso

the ob and o thewell, .e., sticking heworkstringor aretrievable acker,

which couldresult romprematureetof the cement.This is palticularly

tnre n thecaseof a circulationsqueeze. or theseeasons, t eastonehour

of safetyactorshouldbe usedwith mostsqueezeobsandasmuchas wo

hours or circulationsqueezes.

Fluid nss Test AppendixF of API Sgec10

The API fluid loss estprovidesa measure f the rate at whicha cement

slurry oses iltrate(the luidity water)when heslurry s placedagainstpcrmeablemembrane325meshscreen) ndadifferentialpressuredp) s

imposed. This test ndirectly givesan indication of rate and extent of

cementilter cakebuild up.

It hasbeen ound thatonly fluid loss ests onducted t simulated ottom

hole temperatureBHT) and a dp of 1000psi provideuseful nformation

concerninghebehavior f the cement lurry n thewell. A comparison f

30-minuteAPI fluid lossvalues aken underconditionsof LTILP (80"

F/100psi)or HT/HP(BI{T/1000psi)areshownn Table II.

t 4

appropriateor squeeze ementing or two reasons. StQrE



TABLE III

HIGH TEMPERATURVHIGHPRESSURELUID LOSS

oF SQUEEZECEMENTINGSLURRIES

SIMULATED

BHCT API RETARDER 30MIN. API FLLIIDLOSS(ml)

DEGREESF} SCHEDULE %O(BWC\ LTILP HT/HP

159

186

2t3

242

16 10.8

t7 0.2 rl.2

18 0.3 7.4

19 0.4 6.8

4u392

839

1080

API CLASSH CEMENT0.870BWO n-A

127oBWW)NaCl

4.8GPSMD( WATER

From: Proceedingsf SPESqueeze ementing ymposium,Ref6)

CorpusChristi,TexasMarch2,1976

It is obvious rom the dataof Table II thatnot only do theLTll-P fluid loss

data ack agr€ement ith themorc ealistic ITAIP data,but also he rendof

the datas notprcdictedby the LTILP dua

Slurry iltration atecontrol s requiredor theprimarycementing f casing

stringsn annulihavingess hanone nch(1")of clearancend/orn holes

having ong intervalsof high permeability ormationmaterial exposed.

Slurries avingHT/HPAPI fluid loss atesof 400-500ml in 30minutes re

adequateor mostcasing ementing perations.

Verynarrowannular learancesreencounteredn most iner cementations.

Because f this,extentof cementilter cakedepositionmustbecarefully

controlled o preventannularblockage.50-100ml API in 30 minutess

acceptableor most inercementinglunies.

1 5



5 .

For a squeeze ementingslurry to perform its intended unction, it is

necessaryhatcement olidsbe depositedn thetarget ntervalas ilter cake.

If the extentand ateof filter cakedepositions too ow, the nterval will not

rcmain fiUed. If the extentand ateof filter cakedepositions toohigh,the

entire ntervalmaynot betneatednd hework stringand/orpackermay be

stuckby excessiveilter cake. The degreeof cement luid loss control

requircddr:ringa squeezeob depends n severalactors,whichvary from

place o place. ThesencludeBHT, lengthof interval open, ormation

matrixpermeabiliry,work string/casingnnular learance, hetherapacker

is used,ypeof job (circulation r other),andanticipatedqueezeressure.

The HTAIP fluid lossrates of most squeezecementingslurries are

adjustedo t 100ml API in 30minutes.

Comprcssiveuengrthests Section andApoendixD of API Spec10

For thedercrminationf compressivetrengthsccordingo Section and

AppendixD of Spec10, sarnples f the cementslurry to be testedare

pourednto 2-inchcubemolds.The cements thencuredaccordingo the

appropriatcime/pressure/temperaturccheduleound n TableD.1 n Spec

10. The resulting ubes f setcement rebrokenn compressionsing he

proceduresescribedyparagraph.9(page18)of Spec10.

A recentlydevelopcd on-destnrctiveompressivetrengthestingmethod

involves heuseof a device,which s referredo as an UlrasonicCement

AnalyzerruCA) (Ref 7). In the useof the UCA, 300 milliliters of the

cementslurryto betested repourednto the UCA cell; temperaturend

pr€ssurerc mposed n thecement ample ccordingo ascheduleuchas

those ound n TableD.l of Spec10. The nansit ime of a sonicsignal

through he samples continuouslymeasurednd hecompressive trength

is displayedand storedn the associatedofrwareof the UCA. At anytime

the softwaremaybe queriedand the snengthdevelopmenthistory of the

samplewill bedisplayed n anx-y plor The UCA is very convenient nd t

canbe used o produce largearnount f data it is particularly uited or

monitoring he ratc of strength evelopment ndmeasurementf cement

aansitiontime, i.e., time required or cement o conveft from a liquid

suspensiono a solidhavingmeasurabletrength.The data rom the UCA

shouldbe usedwith the undentandinghat hereare actorswhich affect he

cement'sransit ime other than compressive trength;wo of panicular

1 6



interestare cementdensity(i f not 16 ppg or 120 pcf) and curing

temperamreif not 80' D. If knowledgeof the absolutevalue of the

cement's ompressive trength s needed,UCA compressive trengths

shouldbeverifiedusingcrush-testompressivetrenglhsdescribedn the

above aragraph)or cement uredunder he same onditionsor the same

periodof time.

Compressivetrength ataareusedo determinewaiting-on+ementWOC)

tirc, rnonior qualitycontrolanddetectheeffectof anydeleteriouscaction

to which hesetcementmay beexposed,.e.,SO-2+ontainingwaters, cid

gases r BHT > 250'F. WOC time is determined y measuringhe set

cement'sompressivetrength ftersuccessivelyonger ime ntervalsand

then resumingoperationson the well when the compressive trength

reaches certain evel. Followinga primarycementob, drilling can be

resumed hen hecement ttains compressivetrenghof 500psi.(Ref1)

After a whipstock luggingoperation, rilling off theplugcan be nitiated

whenthe compressive trengthof the cement s greater han formation

compressivetrength.Convenely,a ost circulationplugshouldbedrilled

before he strengthof the cementplug exceedsormationcompressive

strength.A well shouldnot beperforatedollowing a primarycementob

until the cement ompressivetrengths greaterhan2000psi.(Ref8) A

cementrlter cakedevelops ompressivetrength t a faster ate and o ahigher level than does he bulk slurry from which the filter cakewas

derived; his s shownby the daa of Table V.

This propertyof cement and cement ilter cake) is important n a

considerationf suitableWOC timefollowing a squeezeob. The usual

recommendationo wait for the development f 1000psi compressive

strengthn theparcntsqueezeement lurry s reasonable.

t 7



TABLEIV

COMPARATTVESTRENGTHSOF SETCEMENTS

AND CEMENTFILTERCAKE

(AfterReference)

Strength f SetCement

AfterCuring

24 Hoursat

Strength f Cement

Filter CakeAfter Curing

8 Hours at

800 si 3,000 si

9LE r40'E

FluidLoss

Agent(Percent)

0.0

0.8

1 .0

t .2

0.0

0.8

1 .0

t .2

800psi

9T.E

2,085

980

800

580

2,085

2,075

1,975

1,920

3,000 si

140'E

4,545

3,515

3,440

3,525

4,545

4,000+

4,000+

4,000+

2,400

2,080

400

3,160

3,400

3,284

12,400

12,200

12,100

12,000+

12,000+

12,000+

The usc of compressivestrengthdata for quality control involves

comparisonof the strengthdevelopedby a freld cementsample o a

standard,.e., as found in API Spec10, or to comparable ata or a

laboratory-formulatedement ample.

In the useof compressive trengthdata o observehe effectsof SO4-2

containingwatersor acidgases,denticalcement amples reprepared; alfare cured in water and half :ue exposed o the potentially damaging

chemical. Both setsof samples re curedunder denticalconditionsof

tempenrturendpressure.Samples reperiodically emoved,broken n

compression,nd he rcsultsarecompared.

1 8

Typically,



monitoring he effect of elevated emperatures>250' F) on cement

compressivetrength, ements curedat the elevatedemperatureusual

curingpressurcs 3000psi),and he compressivetrengths f samples re

periodicallymeasured. f the samplesndicatecompressivenength

reductions with time, insteadof increases, ensitivity to high curing

t€mperatues indicated

Measurementf CementRheolow.Calculation f Cement ressure

DroosandFlowReeime Aogendices andJ of API Spec10.

The frictional prcssureattributable o aprimarycementslurry in both the

plpeandannulus anbcof importancen detennininghydraulichorsepower

necessaryor a givenoperation.Also, in somewells the total pressure

(including rictional) exefiedon sensidventervalsmustbeconsidered.The

significance f cementlow regtmes discussedn theprimarycementing

chapterof thissection.

Arctic CementineestingProcedur€sAopendixK of API Spec 0

Proceduresor the testingof thickening ime, compressivenengthand

freeze-thaw ycling behaviorof cementsntended or use n wells that

p€netratehepermafrost redescribedn AppendixK of API Spec10.

Determinationf TestConditions

In theprcceedingaragraphsf thismanual everalAPI well cementests

are described.The properapplicationof each of the tests with the

exceptionof the freewater est describedn Section6 of API Spec10)

Theoperatinghickening

time test schedulesdescribedn AppendixE of API Spec10)provide

simulatedBHCTs for wells over a range of depths;selectionof the

appropriate cheduleor a given well depends n knowledgeof static

temp€ratureradient 'F/100 t. of depth for that well. Theseschedules

(AppendixE) arealso usefulfor the API fluid-loss test (AppendixF),

rheological properties(Appendix H), and operatingfree water test

(AppendixM). The API operating ompressivenength ests Appendix

M) dependon a knowledgeof static temperature radient o establish

simulatedBHST for testing. Static emperatureradients an be derived

6 .

7 .

8 .

1 9



E.

from downholeemperanuemeasurementsadeduring shut-inbottom-hole

pressure eterrrinations,rom known ield or regionalgradients nd hey

can becalculatedrom loggingtemperaturesccordingo themethodof

DowdleandCobb Ref.9)

As was discussedn the hickening ime section,API thickening ime test

schedulesannot eappliedo all wells.For suchwells,customhickening

time scheduleswhich can be basedon actualBHCT measurementsr

computersimulationsarc needed. A commerciallyavailablecomputer

program "Welltemp"), which is suited o thispurpose,s describ€dn

Reference10. This computerprogram,which runs on IBM PC or

compatibles availablerom EnertechComputingCorporation, 847San

FelipeRoad,Suite1000,Houston, exas77057.

CementSlurr.v esign

As a fint step n designing slurry or a wellcementing pplication,heAPI class

of cements selected.The selections usuallybased n the suitabilityof a given

cement lass or aparticularob, or perhaps n the availabilityof anAPI cement

classn a locale. Then hetype and amounts f additives o suit the slurryfor a

sPecific Peration rechosen. frs

The trro most mportantprincipals o considern effectiveslurry designareto

observe orrectwater equirementsor the cement ndadditivesseepp. 18-19of

Section 30/Iof Reference1),anduse ealisticwell conditionsor thepre-job

laboratory esting,The mostsignificantof thewell conditionsare emperatures.

1. NeatCement lurries

.-tS are definedas suspensionsf

J- Slurries f this ypear€simpleandeconomical,ut he utility of

neatcementslurriess limited by the nability to control theirpropertieso

suit the needs f a varietyof wells. Usingslurry densityas an example

this ackof conrol is illustrated y thedataof TableV, below.

2 0



TABLEV

WATERREQIJIREMENTS ND DENSITIESOFNEAT SLURRIESOF

COMMONLYUSEDAPI CEMENTS

APICernent WaterRequirement

Class gallonVsackgps)

SlurryDensity

lbVgal(pp ) lbVft3 pc0

5.2

5.2

6.3

5.0

4.3

additive-containinglurries.

2. Additive-ContaininsSlurries

A

B

cG

H

15 .6

r5.6

14 .8

15 .8

16 .4

tr6.7

r16.7

110 .7

rt8.2

122.7

It is apparentrom the data n the above able hat the densitiesof neat

slurriesareunique o theparticularAPI classof cement, nd herangeof

slurry densiticsattainableby API cementclassess narrow. {ilF

material, particularly with regard to achieving a hydraulic seal. i=

this applies o bothneat comentslurriesand

Thegeneral ffects f additives nthepropertiesf wellcements regiven

on pp. 30and 31 of Reference . A listing of additives vailablerom the

fornprincipalservice ompaniess givenasAppendixA to this section. n

thc following chaptenof this sectionhe usesandeffectsof additives re

describedn detail.

As excePtionso

the above,the concentrationof a water soluble additive used n relatively

large arnounts, .e. NaCl, is usually given as weight percent basedon

2 L



weight of water, and the concentrations of#

It may be necessaryo lowercementslurrydensity o reducedown-hole

hydrostaticpressureand avoid fracturingthe formation,or it may be

necessaryo raise cementslurry density to increase he down-holehydrostatic ressureo avoida well controlproblem. Sincedensity ontrol

utilizing neatcementsluries is insufficient, t is necessaryo utilize

additives.Additivesused or thispurpose unctioneitherby virtue of their

specificgravitybeingsignificantlydifferent rom thatof cement S.G.=

3.14)or by theeffectof theadditive nthesolids/wateratioof the esulting

slurry.

3. Controlof Slurr.vDensity

The designdensitiesor someslurriesare given in handbooks, .e.,

Reference 1,but for many slurriest is necessaryo calculatehedesired

density. An exampleproblem seebelow)canbe llustrativeof someof the

principlesdescribedbove. Consider low densityslurrydescribed s a

70-30(by bulk volume)ClassG - Pozzolan lufry with 4Vo by weightof

blend)bentonire,ndcalculatehe slurrydensityand slurryyield (in ft3 of

slurryper sackof 70 - 30dry blend). This calculation an bemadeusing

the ollowingrclationshiP:

Slurrvdensiw=vol. of cement vol. of additives vol. of water

PhysicalPropenies ndWaterRequiremens f Components

WaterRequirement

5.2gals 94 bs.

3.75 als74Ibs.

1.3galsZVo sk.ofcement

Component

ClassG Cement

PozmixA

Bentonite

SpecificGravity

3 . 1 4

2.46

2.65

) ' ,



Comoonent Wt Obs)

ClassG

PoanixA

Benonite

Warcr

66.0x 0.0382 alVlb22.0x 0.0487 alVlb=

3.5 x 0.@53Bals/lb

59.8x 0.120 BalsAb151.3bs

Conversion

3$sr-*

Absolute

Volume

gals

2.52

r.07.0 . 1 6

7 . 1 8

10.93 als

Water

Requirement

gals

3.65

1 . 1

2.42

7 . 1 8

Water equirement 7.18gaVsackf 70-30blend

Slurryyield= 10.93galsl/.48gals,/Ftl 1.46Ft3/sack f blend

Slurrydensity 151.3 by10.93als 13.8ppg

* Frompp 14-15,8 of Section23DlIf Refercncc1

Note hat bothof the additives avea lowerspecificgravitythanclassG

cement,but of evengreater ignificance,cgardingslurry density cduction,

is thehighwater equirement f bentonite.Thereareotheradditiveswhich

canbe used o formulate uitableight wcightcement lurries in the ange

of 12ppg oneatslurrydensities). headditiveshat unctionby virmeof a

highwaterrequirementncludesodiummetasilicatein

dry orliquid form),

calsined lay ncludedduring hemanufacnringof the cement examplesn

the USA are Trinity Litewate and TXI Lightweight cements),and

prehydratedentonite. f bentonites allowedo prchydraten freshwater

before hecalcium- ich cements added,he amountof bentonitemay be

reduced y a factorof 3.6. For example, lTVo bwc)bentonite/class

slurryhasa densiryof 12.8ppg, f the bentonites dry blendedwith the

cement. If the bentonites prehydrated,3.33Vobwc) of bentonites

rcquiredo fomtulatea12.8ppgbentonite/classcement lurry. Additives

that depend rimarilyon ow specificgravityto lower slurry densitynclude

diatomaceousarth,perlite and gilsonite. Gilsonite also has bridging

characteristicshichmaket well suitedor lost circulationapplications.To

forrrulateultralightwell cement lurriesdensitiesn the angcof 8.5 12.0

ppg) t is necessaryo usegasasan additive.Thegas naybe n the orm of

dispersed ubbles foam)or encapsulatedn hollow glassor ceramic

spheres.

2 3



High densityslurriesare formulatedby usingadditiveshaving specific

gravityhigher han hatof cementand by minimizing hewater o solids

ratio to the extentpossible. If available, fi

t+YfgffffCEJr wcler

The waterrequired by ClassH

cement anbe rcduced ven urther from4.3 gps o 3.4gps)by the useof

0.75Vo wc of a dispersant uchasHalliburton'sCFR -2. The5-

(S.G.of 4.23 and

water equirement .46galsper 100 b. sack) (S.G. of 5.02

and water requirementof 0.36 gals per 100 lb. sack). Hematite

(Halliburton'sdesignations ID-3) is the obviouschoice f maximum

slurrydensity ncrease ffect s desired. The formulationof a 19.5ppg

slurry can be illustratedby the following slurry density and yield

calculation:

Component Wt 0bs) Conversion

Factor*

Absolute

Volume

gals

3.59

.06

0.723 .51

7 .88

Wuer

Requirement

gals

3.4

. 1 13 . 5 1

ClassH

CFR.2

HD.3Wacr

94.0 x 0.0382 alVlb

0.7 x 0.@23galsAb

30.0 x 0.0239gals/lb29.2 x 0.120galVlb

153.9bs

Water equirement 3.51galVsackf cement

Slurryyield= 7.88galsfr.48galVft3= 1.05 t3lsack

Slurrydensity 153.9b$t.88 84ls= 19.5ppg

* Frompp 14-15 and18of section 30/Iof Refercnce 1.

4. Slurr.v ensitvMeastrementAppendixC of API Soec10

Measurement f slurry densiryprovidesa meansof monitoringslurry

qualirycontrcl both n the aboratoryand n thefield- All well cementing

slurries neatand additive-containing)must be mixed at the design

water/solidsatio, andslurrydensitys a directmeasure f this mponant

designparameter.

2 4



5 .

AppendixC of API Spec10 describesheproceduresor performing lurry

densitymeasurementssing eithera mud balanceor a pressurizedluid

deniity balance.Thepressurizedalances preferredor siurrieswhich

tend o entrainair whenmixed. Someorganicadditivesand NaCl, .e. n

seawater,esult n slurryair entrainment.

SlurrLConsistencyndFreeWater Section andAppendixB of

API Spec0

An important tepn theslurrydesign rocesss verification hat he useof"b@k" values or water equirementesult n a slurry having acceptable

consistencynd ree wateroccurenceharacteristics. he reason hat his

step s neededs becauseement ndadditives anvary from time to time

and rom place o place; therefore,ncremental djustments f water o

solids atio may beneededor aparticularslurry.

It hasbeen ound hata slurryshowing consistencyf ll ABc + 2 ABc

atter20 minutes f stirringatroom empefture n anatmospheric-ressure

consistometer nd free water occurence f < 2.5 mL after standing

quiescentor 2 hours s acceptable ith regard o water/solidsatio. This

easilydone est s patterned fterthe API water content est which isdescribedn AppendixB of API Spec10 Ref2).

Alterationn Rateof Set

The additivemostoftenusddor thispurposes CaCl2.Theeffectof CaCl2

on boththe thickening ime andearly timecompressive trengthof API

ClassA cements shownbv thedataof TableVI whichwas aken rom

Reference.

6 .

2 5



TABLEVI

EFFECTOFCALCIUM CHLORIDE JPONTHE THICKENINGTIME

AND COMPRESSN/E TRENGTHOFAPI CLASSA CEMENT

Waler atio:5.2gal/sk.Slurryweight:15.6b/gal.

Thickening ime hours:min.)

API CasingCementingests orSimulatedWellDepth ft )ol

API Squeeze Cementing Tests fo rSimulatedWell Oepth (tt) ofalcium

Chloride(percent)

0.02.04.0

CuringTime

(hours)6

122448

h

1 224

6't2

24

Notr: N.S. ' No t Sct.

1,0@ gooo 4,ooo 6,000 1,000 4000 4'000 6,000

0:580:300:23

2:231:100:58

4:t$1:550:50

444

4:121:4il0:32

2:{1:60:50

1:520:540:37

3:30 3:81:30 1:200:48 0:53

Compressive trengthpsi)

At Atmospherlc ressure,and Temperature f

At API CuringPressureandTemoetaturef

CalciumChloride

(percent)0000

222

8@ psi

950F

1,600 si1100F

8601,5253,6805,280

1,7002,8505,025

1,7n2,6004,540

400FN.S.N.S.

30s05

N.S.55

4t5

N.S.1 5

400

N70

9102, 10

460785

4m755955

2,4n

7S405

1,9303,920

8501,5403,980

1,095r,6753,980

2351,0652,7't04,8n

1,1702,3604,450

1,2252,3254,550

Some ommentsegardingheuseof CaCl2asa setacceleratoror cement

follow:

Its use at any

Theeffective oncentationangeor CaCl2s04Vo(bwc). Theuse

of concentrationsn excessof 4Vo(bwc) doesnot result in

significantly reater etacceleration.lso, hehigher oncentrations

(in excess f 4Vo)have he undesirableffectsof causinga higher

cementexothermand the durabilityof the set cements affected

adverscly.

The effect of the

addition of NaCl to cement is not as straight-forward as is the casefor

2 6

concentrarioncsuls nrytr



z=oG-.uJ

troz2LlJYII

CaCl2.Themannern which he hickeningimeof an API ClassG cement

respondso changingoncentrationsf NaCl s shownn Figure8.

Figure8

PERCENTSALT BY VTJEIGHTF WATER

Effect of salt on thickening timeAPI ClassG cement.:

The dataof Figure 8 show a decreasen thickening ime, i.e. accelerationn

rate of set,as theconcentrationof NaCl in the mix water is increased rom 0

to about 5Voby weight of water(bww); as heNaCl concentrations further

increased o half-sanration (187obww) the degreeof acceleration s lessand the effect on thickening time of lSVobww NaCl is similar to the effect

of }Vo. Although seawatershowssomegeognphical variation in saliniry,

averagevalue for NaCl concentration s about 3Vobww and about 0.77o

bww for Callvlg Cl2. Therefore, f usedasmix water for cement,seawater

accelerates he rate of set of cement, as compared to fresh mix water.

Between 187obww andsaturation 36Vobww) the NaCl functions as a set

rctarder. (or retardereither) or

well cements ecause ny aqueousluid contaminationhat results n

alteration f NaClconc€ntration ill haveapronouncedffecton thickening

time. Also, t hasbeenound hatsetcementsavinghighconcentrationsf

NaCl are more sensitive o attack by acid gases han are low salinity

cements.

The useof sodiummetasilicateSMS) o lower the densityof cement

slurrieswasdiscussedn a preccedinghapter f this section.SMSalso

accelerateshe setof cement.

8.OOOFT. API CASING TEST

0

2 7



7 .

Retardation:A set etarders usedmore commonly hanan accelerator

becausehecementhydration caction s drivento completionmorequickly

by the higher temperaffesencountered ownhole(seeFigure5). The

chemicaladditivesmost often usedfor this purposeare Ca or Na/Ca

lignosulfonates,.e., Halliburton'sHR-4 or HR-7, thesecompunds rerecommendedor bonom hole circulating temperaturesBHCT) up to

175'F. Modified(purined) ignosulfonatesFlalliburton's R-5)are used

atBHCT up to 210' F. At higherwell temperauresn theBHCT rangeof

210' F - 400' F, a combinationof calcium ignosulfonate nd saltof an

organicacid s used;Halliburton'setarderitting this descriptions HR-12.

The activityof this astclass f retardersanbeenhancedy theadditionof

sodiumetraborateecahydrateBORAX);BORAX s usedn the angeof

1:1 o 4:1 n conjunction ith a retarder uchasHR-12. Manyfluid loss

additivesFI-A) (discussedext)also etald; n somenstances,f fluid loss

control s needed or a slurry,a singleadditivecan performthe dual

Fl-A,/retarderunction.An example f this ypeadditives carboxymethyl

hydroxyethylcelluloseCMFIEC),which s soldasDiacelLWL; CMI{EC

is an effective etarderatBHCTupto 250' F.

It is importanto select rctarderhat s intendedor use n the emperature

rangecorrespondingo thatof the well. A moderate-emperatureange

retarder s ineffectiveat highertemperaturesnd if a high temperature

retarder s usedat lower tempcratureshe required concenrrations

unmanageablyow.

FluidLossRateControl

Severalyearsago, bentonitewas the only fluid loss additive (FLA)

available.Now polymer ypeFLA's, .e.DiacelLWL andothermodified

celluloses, ypified by Hallibunon'sHalads,are the most widely usedmaterials. The choiceof a fluid lossadditiveshouldbe basedon the

temperaturef use aswith retarders) nd alsoon the salinityof the mix

water.MostFLA'shavean effectiveconcentrationhreshoid,hat s, they

show ittle activity until a certainconcenuations reached. For many

FLA'S, this concentrations 0.75 - 0.8 percent bwc). Most of the

polymer-type LA's retard he setof thecement.In some nstances,his

sideeffectmaypemrit heFI-A to performdoubledutyasFLA and etardeq

2 8



8 .

in otherwells, overretardationmayresult and acceleration f setwill be

required.FLA's ntendedor use n low temperaturepplications80-125'

D arenow available;an example f a ow temperanreFLA is Halliburton's

Halad-4.Thisclassof additivenot only is non-retardingt provides ome

set rccgleration.

Conrurcssivetreneth

As was noted n thecement estingsection, he minimumcompressive

strengthequiredof a setcement ariesaccordingo the application.For

mostcementsn most wells the attainmentof minimum acceptable

compressivetrengths not a problem. There are two sinrationswhich

requirespecialattention.Most low densiry ormulations o not develop

2000psi compressivetrengthequiredof a completionntervalcement,

withina reasonable OC time. As an example, ompressivetrength ata

foundonp.3of Section 30N of theHalliburton RedBook"(11)show12

hour compressivetrengthor neatClassA cement slurrydensity15.6

ppg)curedatlz}'F as1905 si. The same lassA cementmodifiedby the

additionof 6Vo wcbentoniteslurrydensityof 14.1ppg)curedatthesame

temperaturendicateda 72 hourcompressivetrength f 1710psi. This

effect of higherwater/cementatio is inevitable,and t helpsexplain he

primarycementing ractice f usinga low density, conomicaleadslurryfollowedby a neat-densityail slurryplaced ver he ntended ompletion

interrral.

The othersituation equiringspecialattentions for cementusedn wells

havinghighBHST(> 250"F). Setcement t BHT 250"F will undergo

loss of compressive trengthand ncreasen permeabilitybecause f a

changen thehydratedC2Scomponentrom theF Oeta) o the o (alpha)

form. This rctrogressionanbepreventedy the additionof 35-40percent

.(bwc) silicato the cement.The silicamustbenominally 160meshor finer

frac sands not suited or thispurpose.There ue two typesof fine silica

that may be used. One s referred to as silica flour (Halliburton's

designations SSA-1), ince ilica lourhasa water equirementt is suited

for high temperature/reducedensityslurries. The other fine silica is

properly cferredo asOklahoma 1silicaor fineglass and Halliburton's

designations SSA-2);his silicadoesnothaveawater equirementnd t is

[utL"'t ttu l

2 9



suited or usc in high temperature/increasedensityslurries. Greatest

benefit of silica occursat a concentration f 35-40 percent bwc);

concentrationst_.22 percentbwc)silicaaredetrimental.

9. Conclusions

Cementslurries or well cementing re designed y first consideringhe

requirementsmposedon thecementand he environmentnto which the

cementwill be placed.A cementslurry intendedo satisfy he above s

preparedn the aboratory nd estedor suitabiliry.Necessaryhangesn

slurry designcan henbemade,asneeded, ntil the slurry s right for the

intended pplication.

3 0



m. PRIMARY CEMENTING

A. Introduction

Primarycementing anbe definedas heplacingof cementn the annularspace

betweenhe outsidesurfaceof steelcasingand the boreholewall or, in some

instances,he inside surfaceof previouslysetcasing. This is accomplishedy

pumpingcement lurrydown he entire engthof thecasingoutthe bottomoint and

into the annularspace.The cements thenallpwed o setbfore drilling is resumed

or thewell is cornpleted. he cementing f several asing trings ndaproduction

liner in an examplewell is shown n Figure 9 from Reference3.GIF;P

ry

Figure9

CasingProgram

Tygr crsing

Conducior rting

Typlcrld!9lhc, tl

20.no

Surlrct c.ring

2n - 4WInlamadiata casing

llcmg nol 3hown ncludtcaJng hrrdwrrc .nd tiabrckcuinC. Tha tirback caring

conncct! rl tha lin.r looand arlandt lo lha 3urtaca.

ffil c.'.nr

2,000 30,000

Thesetprimarycementsheath erformshydraulicandmechanicalunctions. The

proper erformancef thehydraulicsealing)unctionachieveshe ollowing:

Exclude xtraneousluids rom theproductiontream

3 1



* Confinestimulationreaoncntso the argetnterval

* Confinesecondarynd eniary ecoveryprocesses

* Casingshoesmust be sound o accomplishwell control n eventof a

P'roblem

* Exercise ontroloverproduction atternsreservoir ontrol)

* Prwentexternal asing orrosion

* Preventcontaminationof freshwater aquifiers by formationfluids. This

function s of particularmportancen wellsused or disposal f producedbrines.

Setcementmustdevelop ufficientmechanicaltrengtho:

* Not shanerwhenperforated

t' Providecasingsupport

* Absorbdrilling shock

* Preventcasingbuckling

* Supporrhe formation. This is of particular mportancef halite (NaCl)

interyalsar€penetrated

C. SubsurfaceEquipment

The rnost mponant temsof primarycementing ubsurfacequipment reshownn

Figure10(takenromReference2).

1. GuideShoe

The guideshoecan bean open-end ollar,with or without a moldednose; t

3 2



Figure10

SubsurfacenimaryCementing quipment

3 3



2.

is run onthe irst oint of casingandguideshe casing ast rregularitiesn

thehole. Circulations established own hecasingandout the openendof

the guide shoeor throughside ports. Side ports provide a meansof

maintainingcirculation f the casing estson bottomor is pluggedwith

cunings. i

Float Shoerto[ar

The "float" whether t is incorporatedn the shoeor a collar or both s

basicallya backpressureheckvalve. The valve prevents luids from

entering he casingwhile pipe is lowered nto the hole. This resuits n

reducing hehook oad. Depending n the depthof thewell, thedensityof

thedrilling fluid in theholeand hecollapseesistanceatingof the casing,

it maybenecessaryo partially ill thecasingwith drilling fluid from thesurface s t is run to preventcasingcollapse. Examplecalculations

illustrating hispointfollow:

Consideran 8300 foot well with 12.5ppg drilling fluid in the hole

into which L7lbltt 5 ll2 K-55 casingwill be run. The hydrostatic

pressure mposed by the drilling fluid at the bottom of the hole

would be

l2.5lbtgat.x300t x .052m=

5395 si

and the minimum collapsepressure ating of 17 lb/ft K-55 casing

(p. 56 section200of Reference 1) s 4910psi. This casingstring

shouldbe able to resist hydrostaticprcssure o a depth of

r2.Slblgat.xft x.052m= 4910 si

Dft =7554feet

soatleast he bottom

3 4



8300-7554eet= 746feet

should e rlledwith drilling luid as hecasings run nto thewell.

TherearedifferentiaVautomaticill-up shoes vailablewhichwill permit he

casingo fillto some redeterminedxtent usually907o r SlVo z).These

devicelardnotwidely usedas heyare ess eliable hanconventionalloat

equipment,ndconventionalloat equipment ffersmorccontrolof extent

of fill. Differentialfill-up equipment asbeenpromotedas a means o

reduce rcssurc urgeswhile casings bcing un. The equipment asbeen

found o be neffective or thispurpose.Oncecasinghasbeen un to the

desired epthcirculations establishedhrough hecasingand loatvalve

and up through he annulus. When the pumpingof cementslurry is

completed,he back-pressurealvepreventslow backof cementnto the

casing.A float collar,whichcanbeplaced1-3casingointsoff bottom, as

u advantagevera float shoen that hemud ilm andotherdebrispushed

immediately head f the opcementingwiperplug will remainnside he

casingnstead f beingdepositednto thecriticalshoeegionof theannulus.

CementingWiperPlues

The use of

Also, heseating f the opwiperplugat the loat collarprovides pressul€

indicationwhich signalstrat he ob hasbeenpumped.

The top wiper plug is solid rubbeq he bottomwiperplug has a hollow

core,which s covered y a rubberdiaphragm. t is importanthat henvo

plugsbe nsertednto thecasingn theProper equence.When hebottom

plugseats t the loatcollar, he diaphragmsrupnred bypressuring p and

thecementob ispumpedhroughheplug. If the opplugshould erun n

thebottomposition,he ob cannotbepumpedhrough he solidplug;the

cement lurryca,nnotereverse irculatedrom the casingbecausef the

checkvalve actionof the loat,and heoperator asarealproblem.

Centralizers

To achieveadequateemovalof drilling fluid from the annulus t is

importantthat the casingbe centralizedso the cementslurry will be

J .

4.

3 5



presented ith a symmetricallow path. Centralizers lsohelp prevent

stickingof the casingand keep the casing rom enteringkey seats.

Centralizations accomplishedy placingcentralizersn thecasing;bow-

springcentralizers reusedn openhole sections, nd igid-type nsideof

pipe. API Spec 0 D (Ref 13)definesminimumstrengthequirementsor

centralizersarrying heAPI monogram.These equirementsrebased na

startingforce and a restoring orce. Most servicecomPanies rovide

recommendationsn theproperplacement f centralizersased n casing

load,holesize,casing izeandholedeviation. fi

monogrammedentralizers;hey should e ocatedn gauge ections f the

hole if possible),nd heyshouldbesizedo nominalholesize+ U4".

5. Scratchen

Scratchersre another lassof hardwarehatmaybeattachedo the casing.

Thereare wo typesof scratchers those hat areusedwhen he casings

rotatedand thoseusedwhen the casing s reciprocated.SeieflgS-3r

.ir,cffectinc-onlvf thecasint'ismovedwrhile .*'-' ^'-

| !lllFlfl$e

;hele. The effectivencssof scratchers as alwaysbeen open to

qucstion;someskepticsstate hat the only bcnefit of scratcherss to

encouragehe operatoro move hepipe.

D. Surface ernentineouipment

Well cenrentings accomplishedsinga dry blendof cement ndadditives,which

is mixedwith water,and henpumped ownhole. Alternately,headditivessolid

or liquid) may bc added o themix waterand his "solution"is mixedwith dry

cemento form the slurry. Thercfore, urface quipmentequired o mix andpump

a slurry ncludedry blenders r liquid injectors,bulk transporters,lurrymixers,

pumps, lurrydensiometer,ndcementingead.

3 6



1 . Drv Blenders

Bulk dry additives,.e. barite,hematite, entonite, ozzolans, nd silica,

areused n relatively argeamounts approachinghe weightof the dry

cement n some ormulations). Chemically-activery additives,.e.

accelerators,etarders,luid loss additives,and dispersants, reused n

relativelysmallasrountstensof poundsof additive n thousandsf pounds

of dry cement).The problemsof producingan effectivedry blendwith

eitheror both ypesue similar: the correctamounts f additivesmustbe

usedand headditivesmustbeuniformlydistributedhroughoutheblend.

This s accomplishedsinga 300-400 ubic oot capacity ontainer uchas

theexampleshownbyFigure1l (Ref1).

TheScCgntainersusually efered to as "blendbottles"or "pods")ate

equipped omaterialcan bepneumaticallyransferrednto or outof thepod

andalsoagitatedwhile in the pod. A recent echnicalpaperentitled"ObtainingandVerifyingQualityCementBlends" Ref 14) eports hat he

main rcasonsor poorperformingblendsare:

Incorrectadditivesor incorrectconcentrations f the proper

additives.

Poorperformancef thebase ement.This s usuallyacementhat

doesnot meetAPI performancepecifications.

All dry blendingmethodsaAagitation,ransferandadmixbottle)

performbest f dry solidsare< 30Vo f the blendbottlevolume.

Theadmix bottleblendingmethods lesssensitiveo blendsize han

arc he othersystems.

LAS (Liquid Additive Systems)

Liquid additivesmay be added o the mix water directly from the shipping

containers or they may be metered into the mix water from an onsite

reservoir using what is often referred to as a LAS. In the use of liquid

additives here areprecautions o beobsewed. If the needed oncentration

of a given liquid additive in a slurry is intended o match the concentration

of a more familiar solid additive, then the specific gravity and Voactiviry of

)

3 7



Figure11

BulkBlendBottles

lZ.---' ------te'---'

* -_:. z- - --.-

5-.:- --_ -E

4-7- t

Aircraft bulk units for use n remote areas.

Land-bascd ulk storageand bleodingplaot. Marine bulk cementing nd pumpingunis.

3 8



the liquid additivemust be considered.This point is illustratedby the

examplc alculation elow:

Consider slurrythatwas ntended o be composed f 100sacks f Class

G cement etarded y 0.5Vo wc of HR-5 (a Halliburtondry retarder);t

wasdecidedo substitute R6L (the iquid equivalent f HR-5).

* weightof drycement:

100sx x 94 bs/sx= 9400 bs

* weightof HR-5 n thedesign lurry:

9400 bs x .005= 47 lbs

Accordingo informationrom Halliburton,HR6L hasa specificgraviryof

1.21 nd s40Vo ctive

* densiry f HR6L s

t.21x 8.33 bVgal= 10.08bs/gal

* and heactivecomponenter gallonof HR6L is

.4 x 10.08= 4.03 lbs

and

* therequiredHR6L for theredesignedslurry would be

ffidt&F,ffir=t''fr'r*

Some iquid additivesare not truly soluble n the mix waterbut are

dispersible.Someagitationof the mix waterwill be requiredas iquid

additivesare ntroduced.

3 9



3 .

Finally, as the most mportantprecaution, he densityof liquid additive

sltnriesmustbecontrolledprecisely. It is important omix any slurryat the

designwater/solidsatio, .e. to the designslurrydensity,so heproPerties

(consistency,reewater,hickeningimeandstrength evelopment) ill be

as specifiedand asexpected. n a liquid additiveslurry (or any slurrywith

additivesdissolvedn themix water) f the slurrydensitydeviates,not onlyis thewater/cementatio changed ut so s theadditive/cementatioand he

effecton slurrypropeities an bepronounced.

CementSlurryMixers

Well cement lurries anbemixedusinga continuousypemixer(referred

to as a jet mixer), a batch mixer, or the more recentlydeveloped

recirculatingmixer (often eferredo nsa RCM). The RCM incorporatesfeannesof both a continuous ndbarchmixer.

The et mixer(picturedn Figure 12 rom Reference 5) wasdevelopedn

l92O; t utilizesa hopperwhich receivesdry cementby gravity from a

storage ilo. The cementalls nto a mixingbowl and s mixedwith water

which s admined thighpressurehrough n orifice.

The et mixer is not limited with regard o quantityof slurryand t is

rnechanicallyimpleand eliable.Theprincipal isadvantagen theuseof a

jet mixer s thedifficulty n exercisingontroloverslurrydensity.With the

introduction f theRCM (in the ate 1970's)hepopularityof the et mixer

declinedand t is now seldom ncountereds hcprimarymeans f slurry

mixing.

A batchslurrymixer (Figure13 from Reference 6) is a tank usuallyof

about100bblcapacity.

The batchmixer s equippedo mix, circulate,andagitate ement lurries.

The mix watermay beplaced n the batchmixer and hedry cement lown

into the waterwhile agitations takingplaceor the slurrymay bemixed

usinga et mixer and henpumpednto theunk for uniformmixing and

densityadjustment.Many prefer o mix the slurry slightly heavier han

desiredn a batchmixerand henaddwater o bringthe slurry o the exact

designdensity. Remember hat surface ime s oneof the actors in the

4 0



Figure12

JetMixer

Figure13

BatchSlurrvMixer

WATERII{LET

CEI{TRIFUGALPUTP

PNEHYDRATOR

RECTRCUtatIXGCETEilT SUCTIOI{

TO OISPLACEMENTPUIIPS

4 l



thickening time equation,sothe time required to manipulate the slurry in the

batchmixer should be allowed for and his surface ime should be observed

on the ob. Two radial axial-flow turbinesand a recirculatingpumpprovide

mixing action and homogeneityfor the slurry.

Halliburton's version of the RCM is shownasFigure 14.

Figure14

Schematicf RecirculatingMixer

Recirculat inc ixermounted n ruck.

A u t r C t v E n lI i l L E I

SuLx cEu€ttCOtrIROL VALJE

V V l x r t oG A TE r

t/ ) t\LEf

SC E tvt r tCR E C I R C U L A T I N GI X E RS Y S T E M

4 2



4 .

Since here s someslurryresidenceime in theRCM, slurry densitycontrol

is more readily accomplished n the RCM than in a jet mixer. For small

volume cement obs, i.e. squeezeobs and plug setting,RCM's are often

usedas small batchmixers. Halliburton's RCM has a capacityof about 7.5

barrels.

Densimeter

For a cementslurry to have its desiredand expectedproperties t must be

mixed to the design density. A working, properly calibrated densimeter

mountedon the cementingunit is useful to the cementerashe has accesso

a continuous readout of slurry density and can make adjustments n

water/solids eed as needed. The printed strip chart display provides a

pennanent ecordof slurryqualiry. Most densimeters tilize a Cesium 137

sourceand a Geiger-counter etectorwhich areattached o a shortpup oint

that s placed n the high pressure ischarge ine. It is important to place he

source n a high pressure ine so the effect of air entrainmenton slurry

densitywill beminimized. The unit is normally caiibratedwith freshwater

in the line and the spancan be set by reference o a known source. It can

also becalibratedby reference o the actualslurry densify,asmeasured y a

pressurizedluid densitybalance AppendixC of API Spec10,Ref 2).

CementingHeads

The cementinghead s an attachmenton the top of the casing to which the

cementing ines are attached. The top and bottom wiper plugs are also

pumped rom thecementing ead. A two-plughead s shownasFigure15.

(16)

Currently in use are single-plugcontainers,double-plugcontainers,and

rotating heads. The double-plug container holds both plugs and allows

continuous operation,once Pumping of cement slurry has started. A

rotating head holds both plugs and allows for casing rotation while

cementing.

5 .

4 3



Figure15

TwoPlugCementHead

DOUBLE LUGCEMENT EAD

TOPC E M E N T I N G

BOTTOMC E M E N T I N GP L U G

E. Primary CementingProcedureso EnhanceSuccess

Controllableroblems

There re somepotentialprimarycementingproblcms hat are not only

connollablebut can be and shouldbe avoidedby properdesignand

execution.These roblems rediscussedelow.

A surprisinglyargenumberof primarycementingobs arenot

successfully umpedbecause f problemswith the slurry. These

failurescanbethe esultof noprcjob estingof thecomposition r

theprejob estingot

beingproperlydone.Other requent ausesf

problems rean mproperly onstituted ry blendor a non-uniform

dry blend-A colorimetricest 17)hasbeen eveloped hichcanbe

usedn the ield to indicate agreement"of the ield dry blendwith

the design dry blendand also he uniformityof the dry blend(by

analyzing everal amples).Also, oneof themorecommon and

completely voidableroblems)s that hecement lurry s toooften

not mixed o thedesign ensity.

7-----V, L---J t

I-\L\ - - - l l7

t t a\ - - l l 7l t l -

\ - l l " /.L--._Jt t:2

\ - l\

- T ? /

\-ll

/I tssssssssssssssss-iiL

s - , 17\ ; - -

117I \ L

1 .

4 4

I - - . ^/ , ' z<ar {€)

i , r pl---4(DVr'



It is desirable o conduct a primary cementingoperation with full

returns. Loss of cement slurry to the formation will result in

uncertainty with regard to top of cement (TOC); this can be

important if the primary cement is required to cover a potential

productive interval or fresh water sanduphole,or if TOC needs o

be placed inside an intermediatecasing string. A coincidental

problem, which can occur if returns are lost, is cement filter cake

bridging in the annulusresulting in loss of the ability to pump the

job. This eventoccurscoincidentallywith loss of returnsbecause

formation material with undamaged by mud filter cake) formation

permeabilityand porosity is exposed o the cementslurry if the

formation is fractured. The relatively high filtration rate cement

slurry can then form a filter cake bridge in the annulusrenderingfurther pumping impossible. l,ost circulation while cementingcan

be minimized by reducing the hydrostatic pressureexertedby the

cementslurry sofracturepressure radientwill not be exceeded;his

is accomplished y reducingslurry density. It is not uncornmono

pcrform a primary cementing operation using a low density lead

slurry and a higher density,high strength ail slurry, soas to reduce

overall hydrostatic oading and still have cement of suitable

properties over the completion interval. Also, lost circulation

material such as cellophane flakes and/or granular material, i.e.

Gilsonite, canbe added o the cementslurry to promotebridging in a

fracturcor vug. So, lost circulation is a controllable problem with

slurry designbeing the principal meansof control. An operational

procedurc that is sometimesemployed to regain returns, f returns

are ost duringcementing, s to slow the pumping rate.

Finally, somecementobs arenot successfully umpedbecause f

equipment malfunctions. The avoidanceof these problems is

primarily the responsibilityof the cementing ervicecompany,but

the operator's epresentative n the ob shouldbe satisfied hat ines,

cementingheadand manifolds have beenpressure ested,and that

therc s redundancy or the critical equipment tems.

4 5



2 . Separation f mud/cementn theoipe

discussedn the SubsurfaceEquipmentSection. It is important to useboth

top andbottom wiper plugs sodrilling mud andmud contaminatedcement

will not be left in the critical casing - shoe region of the annulus. This

undesirable esult can be illustrated by the following calculation. If it is

assumed hat 8500 ft of 29lbs/ft 7" casingwill be cementedusing only a

top wiper plug andthata mud film averaging1132"n thickness s left after

thepassage f thecementslurry, thecontaminatedmud/cementslurry in the

lower part of the well would amount o 6.4barrels. [f Volume 1 (V1) is the

volume of the clean,wiped casingand Volume 2 (Y) is the volume of the

casingwith the U32" mud film and the i.d. of the 29 lbs/ft, 7" casing s6.184" p. 36 of Section 00 of Ref. 11) .

Vr = n rf h =tt (0-25765t)28500 t

and

Yz= nr f h =n (0.25505028500t

Vr - Vz= 1772 u t - 1736 u t = 36cu t

and

36 cu ft (.1781bbls/cu t) = 6.46O,t

If a float shoe s employed,all of the mud would enter the annulusand this

could amount ro 37.35 t/bbi* (6.4) = 239' of mud in the lower part of an

8-314"x 7" annulusor an even longer interval of mud - contaminated

cement, f there is somemixing of the mud and cement. Even if a float

collar one oint off bottom is used n this hypotheticalwell, the capacityof

29lblftT" casing s26'92 ft/bbl**, 26'92 ft (6'4) = 172'and therewould

bemud left in the lower joint of casingandalso n the annulus.

P.44of Section122of Ref.11

P.20of Section 10of Ref. 11

*

* *

4 6



3 . Separationf Mud/Cementn theAnnulusDisplacement)

Adequateemoval f drillingmud romtheannulussessentialo achieving

primarycementinguccess. his aspect f primarycementingas eceived

moreattentionromresearchershananyother. Inadequateemovalof mud

will result n dilutionof thecement lurry,chemical ontaminationf the

cement lurryor channelingcolumnof bypassed udof sufficient ertical

extenthat heres lossof hydraulic ealn theannulus).

Dilution and/or ontaminationf acement lurryoccursf thecement nd

mudmix moreor lessuniformly,unlikechanneling hich esultsrom mud

beingbypassednd hecement lurryandmud emaining ssentiallyntact.

Of theproblemsesultingrom nadequateud emoval, ilution s the east

serious.

Glry

ffi Thewater o cementatiocanbe educed y the

use of a dispersant,.e, Dowell-Schlumberger 'sD-S) D-65, as was

discussedn thecement lurrydesign ection.Theeffectof muddilutionon

cement ompressivetrengthsshown y thedataof TableVII, whichwas

derivedromTable10.1 f Reference8.

TABLEVII

EFFECTOFMUD DILUTION ON STRENGTHOFCEMENT

CuringTime: 12Hours

CuringTemperature:30"F

Mud

Dilution

(7o\

0

10

30

60

CompressiveStrength

(psi)

CementA

29r0

2530

1400

340

Cement

7010

5005

2970

23r5

4 7



CementA is mixedwith 5.2gals.mix waterandhasa slurrydensityof

15.6 pg.

CementB hasa dispenantadded,s mixedwith 3.48gals.mix waterand

hasa slurrydensityof 17.4pPg.

It is not possible to generalizeconcerning the effect of contaminationby

mud chemicalson the cement,since he effect is variable dependingon the

particular mud system. Lignosulfonate mud thinners retard cement set;

thereforecontalninationby a highly treatedwater-basedmud can cause he

cement to be overretarded.The internal aqueousphaseof someoil-based

mudshasa high concentration f CaClz; contaminationby this typemud

cancausepremanre set of the cement. The effectof NaCl on therateof set

of cement was described n the slurry design section; it can accelerateorrctard depending on the concentration, so NaCl in drilling mud or any

wellborefluid is apotentialcontaminant or cement,but its effect s difficult

to predict. The bestapproach o a contaminationproblem is prevention;

preventionof contaminationof the cementslurry while it is in the casingcan

be achievedby the use of two wiper plugs. After the cement slurry enters

the annulus, he useof a fluid spacer/preflushheadof the cementslurry,

behind the residentdrilling mud is used to address he contamination

problem. As will be describedn a following section,a properly chosen

fluid spacer/preflushs also of benefit n achieving emoval of bulk mud.

A variety of techniquesand materials has been developed to achieve

adequate isplacement f bulk drilling mud from the annulus, .e., avoid

channeling. A synopsisof techniquesandmaterials or achievingeffective

displacement,with emphasis n recent elevant esearch,s found in the sub

sectionwhich follows.

a. Displacement

There are three publications which provide background for the

formulation of practicalproceduresandmateriais ntended o resuit

in effectivedisplacanent. Haut and Crook (Reference19) reponed

theresultsof a studywhich utilized a large scale low model (shown

schematically sFigure 15.1).

4 8



Fieure15.1

-The downholesectronot the test aooaratus onsistsof apermeable and tormation n which mud is circulated nd casing ssel as shown.

t

D

' ln

l o

t g

4 9



The test sectionof the flow model (denoted"formation" in Figure

15) consistsof a consolidatedsand 10 ft long with 6 ll2-inch i.d.,

having high, low or no penneability. Most of the experimentswere

performed using a high pemreability test section of about 1 Darcy

pemreability. The test drilling fluids were water-basedmuds with

densitiesn the nmge of 14-17ppg. Sixteen Seventeen pg cement

slurrieswith yield points of 0, 33 or 116 bs/100ft2were employed

as the displacing fluids. To perform an experiment, the system

(everything inside the testing acket) was saturatedwith water, then

the drilling fluid was circulated nto the casingandretumed hrough

the 5-inch x 6-inch annulus or one hour at 3 bpm and temperature

of 180' F; the volume of filtrate lost through the synthetic formhtion

was measured.The heatingoil temperaturewas then raised o 200'

F and themud allowed to snnd quiescent or 24 hours with 100psi

confining prcssuremposed During this period, the mud gelledand

lost additional filtrate, which was measured. There followed a I

hour period of mud circulation at 3 bpm and 180' F. The"well"

was then cementedusing, for most of the tests, sufficient slurry to

cement 1200' of a S-inch x 6 llZ-inch annulus. The temperature

was increased o 230" F and the cementwas allowed to cure for 24

hours. The test sectionwas cooled and samplewafers" werecut so

casing stand-off and mud displacement efficiency could bemeasured. The data developed by this study are summarized by

Figure 16.

It is apparent rom Figure 16that the characteristics f the resident"fluid" (drilling

mud) and the rate at which the displacing fluid (cementslurry) is flowed arevery

important to the efficiency of the displacementprocess. The mud mobility factor

MI,IF) referrcd to in Figure 16 can be defined numerically as

IvIIvIF=Vrffi where

Vr = Volume of mud filtrate collectedduring a test;V6 s not the API fluid loss rate

of the mud. Gtg min = 10 minutegel strengthof the mud. From a consideration f

the data and observationsof the results of these flow tests Haut and Crook

concluded he following:

5 0



Figure16

@

oE

a

(Vetocity)2 Mudmobilityactor

-This graphplots he percenlof mud displaced s a funcllon

ol cementann'ular btocity imes he mudmobilityactor M M F )' As

shown, he percentof mird removed ncreaseswith an increase n

M.M.F., n etfecta decrease n filtrate oss and ge l strength'

o

o

t. It wasobservedhat low of

the cement slurry through the narrow side of the annuluswas difficult toinitiate for even slight asymmetry.

It should be

noted, hough, hat a thin (low viscosity, ow yield point)cementslurrycan

be flowed at higher rates han s possibiewith a thicker slurry, and high

flow velocity of the displacing luid is beneficial(seeFigure 16).

Basedon a considerationof the velocity distribution in a single flowing

non-Newtonian luid, it has beenassumedhat certain flow regimesare

favored or thecementslurry. Since heaxial velocity in laminar flow is not

as uniform across he annulusas s thecase or plug flow or turbulent flow,

somehaveassumedhat aminar flow of the cementslurry is to be avoided.

Actually when a non-Newtonianluid, i.e., drilling mud, s beingdisplaced

by a dissimilarnon-Newtonianluid, i.e.,cementslurry, nstabilitiesat the

interface result in mixing regardlessof flow regime. As a result, the

o

5 1



interfacial profile in an annulusduring a primary cement ob does not

resemble he velocity profile of the displacing fluid. To summarize, he

authorseported

Tr-^ r.t ^ ^---- ' "t". ' | ' ."-^.,-r|rh or to stateheirobservations

somewhatdifferently, a thick (laminar flow) and a thin (turbulent flow)

cementslurry flowed at the same ntermediate low rate will result in the

samemediocredisplacementefficiency (40 - 50Vo).The same wo slurries

flowed at high rates(same low regimesas noted above)will achievehigh

displacement fficiency (> 807o). n all instanceslowing a cementslurry at

plug flow rates esultedn poordisplacement.

o The duthors eported hat differences n densitybetween hedisplacing and

resident luids were not a controlling factor with regard o displacement

efficiency. The supportingdata are shownas Figure 17.

FigurelT

P c - e n = 7 2 k E m r OPc 9m = 360 tgrms A

1 0 0 1 0 r 1 0 2 1 0 3 1 0 4

o

o

l

ts

o

40

(velocity)2 Mudmobilit' actor

-Differences in the densityof cementand mud are not asimportant s the mobilityof the mud, as shown n thisgraph.The

crurveepresentsdisplacement esultswith equal densaties, hile hepoints representresultswith unequal densities.

There are two likely reasons or this. MMF and flow velocity of the

displacing luid arestrongoverriding actors. Secondly,he mmobile mud

hasundergone ellationand iltration; its densitycan be ashigh as 34 ppg,

so densityof theparentmud is not relevant.

5 2



For this largescalemodelstudY

. f f iiwq'-M

(inteweningluid betweenhemudandcement lurry)G (21).

The experimentsnvolving preflushes re discussedn a subsequentparagraph.

The experimentseportedn Reference 9 did not addresshe subjectof

pipemovement.Haut andCrook eviewedan earlierpublicationauthored

by Mclean, Manry,andWhitaker 20)which eportedhe esultsof a study

utilizing a displacement odel hatp'rovidedor movement f the nnerpipe'

Mclean, etal,reportedhatpipemovementreciprocation nd./orotation) s

beneficial.

, f Lateral movementof the PiPe s

anaccompanyingenefitof rcciprocation sa givensection f theannuius

will alternate eweenwide andnanow side.

Hautand Crookurilized heflow modelshownby Figure15 n conjunctionwith

thematerialsnd echniquesescribedn theprecedingaragraphso nvestigatehe

effectivcness f low-density, ow-viscosiryspacer/preflushluids in enhancing

displacementfficiency. Theirresultsare cportedn Reference1. Theyfound

thatwater,187oNaCl bww (bywaterweight)brine,anda low-viscosity '5 ppg

water-based,ormulated pacer ll rcsultedn enhanced ud emoval; omeypical

dataareshownby Figurc18,below. From heobservationsf Haut& Crook,and

alsoMclean, et al, who uSed transparentlow model,a low-density, ow-

viscosity lush, suchaswater,affects he mmobilemud n trvoways. It tends obreakdownhegelstructure,ndsince hemud s heaviert tendso sloughand all

into the essdense isplacingluid.

o

5 3



Figure8

PERCEf{T

TUIUO

RHUIOVED

- D i sp lacemen tes t resu l t s or a heavywe tgh t ud us ingwa te ras a space r

If this s done, hedensiry

of thespacer/flushhould e adjustedo avalue ess han hatof thedrillingfluid so

someof the benefits ited or awaterprcflushcanbeachieved.

An interestingield studyof displacementasbeen eported y Kline,Kocianand

Smith(22).For this study,all of theprimarycementused n severalEastTexas

wells was aggedwitha shorthalf-life adioisotopehicheminedgarnmaaysat an

energydifferent from the natural formation signal. Thc wells were logged

immediarelyaftercementingwith a spectralgammaaytool. In thirrywells drilled

with a 9.2 ppgmud,utilizinga lO-bblwaterpreflush,bow-spring entralizers,nd

casing movement(either simultaneous eciprocationand rotation or just

reciprocation), nnularill by the cernent lurryamountedo more han1007o f the

calculated nnular olume. Thecalculatedolumewasbased n an open-hole -

armcaliper survey.Only oneof thc thirty wells rcquiredaremedialcementingob.

Obtainingmorethan l0O%annular ill is intercsting. This indicates hat themud

displacementy the cementslurrywasvery efficientandalso hat somehole

enlargementccurredwhilerunning asing ndwhile conditioninghemudand he

hole by circulation. The spectralgamma ay log indicated hat the hole

5 4

^ 10BBTSWATER

e 5{lBBLSWATER

NROCITUz MUOMOEITITYACTOR



enlargementsere rregular,.e., s

wit W

2 .

o.* In two wells ncludedn theKline, et al, studydisplacement as ess han

complete.For oneof thesewells casingmovementwasstoppedo allow the top

plugto be dropped;he casingstuckandmovementouldnot beresumed.There

was an obviousdeficiencyof cement o approximately 00 eet above he float

collar. In theotherwell showingdeficientmudremoval,urbolizersvanedbow-

typecentralizers) ereusednstead f conventionalentralizen.Thiswell showed

poor cementcoverage srosshe bottomsands.While it couldbe debated sto

whether r not the urbolizerswere esponsibleor thepoorcoverage,t is evidentthatnobenefitswere calized

Summary

Adequate isplacementf drilling mudduringaprimarycementing peration anbe

achievedy:

Utilizing a drilling mudhavingminimum ime dependentel strength nd

fluid loss,consistent ith gmd drillingpractice.

Cenaalizinghecasing.

Conditioninghemud/hole, ut don'toverdot.

Movingthecasingwhile thedisplacingluids(preflushandcement lurry)

are lowing n theannulus.

Usinga ow-densiry,ow viscosityspacer/preflush.

o Pumpingthe displacing luids (preflushand cementslurry) as fast as

possiblewithout osing etuns.

o

o

o

5 5



F . PostJobConsiderations

After a well has beenprimriry cemented,pressureshouldbe bled from the casing.

If the loat valve(s)areholding, .e., here s no back low, thecasingshouldbe eft

unpressured hile waiting on cement lIVOC). The reasonbeingthat if the casing s

left pressured,f will be expa4ded uring the period when the cement s setting

(converting rom a fluid to a solid). On reducing he pressure,o bring the well in,

the casingwill contractand the cementsheath,now beingrigid, will not conform to

the new reduced O.D. and loss of bond between the cement and casing is

inevitable.

As a second onsideration, ufficientWOC time must beobserved or the cement o

develop adequatestrengthbefore operationsare resumed. For a period of hours

after the plug is bumped he cement s rigid, but hasvery little strengthand any

damage ubstained y thecementsheath uring thisperioddoesnot"reheal". The

required period of WOC time varies dependingon the cement and downhole

conditionsof temperature ndpressure.As was noted n the cement estingsection,

cement used to cementan intermediatecasingstring should have compressive

strengthof at least 500 psi beforedrilling is resumed. Completion ntervai cement

shouldhavecompressive trengthof at least2000psi before he well is perforated.

SpecialOperations

l. StageCementing

Stagecementing onsistsof placement f cementslurry around he lower

porrionof a casingstringusing conventionalprimary cementing echniques.

Successive pperstages an then beplaced hroughports n a stage ollar.

Most stage ementings two-stage, lthoughadditionalstages repossible.

Stagecementing s usedwhen a long column of cement s required and

formations are exposed in the wellbore which will not support the

hydrostatic head, and when two or more widely separated ntervais are

presentwhich must be cemented.The arrangement f equipment or a stage

cementing opelation is shown by Figure 19, which was taken from

Reference 6.

After first stage ementinghasbeenperformed n a conventionalmanner,an

opening bomb s dropped o land in the ower seatof the stagecollar. By

G .

5 6



Figure19

Regular wo-S ageCementing

t

E 7

\

!92

III>rt

''""'.:1"'

5 7



2 .

pressuringup (1200 - 1500psi) the retaining pins are sheared; he sleeve

movesdown, andthe portsareopened. The well is then circulated to clear

the ports and condition mud. Depending on the severity of the lost

circulation problem, some time may be allowed for the first stagecement to

achieve nitial setbeforeperforming the secondstagecementing. In cases

of severe lost circulation in the vicinity of the first stage or a long

uncenrentedntervalof annulusbetween he top of the first stagecementand

the stagecollar, a cenrentbasketor external casingpacker (ECP) may be

placed mmediately below the stagecollar to prevent fall of the secondstage

cemenr. It is important that the casingbe well centralized n the vicinity of

the stagecollar because he stagecollar is a weak point in the casing and

needs o besupportedby a uniform cementsheath,also f the casing s lying

against the wall of the hole the flow ports may be plugged. Since the

displacementenvironmentduring the secondstage s not ideal (the casingcan't be moved) centralizationof the casing, use of a low density, low

viscosity preflush and careful conditioning of the mud all becomevery

important. In the caseof a deviatedwell, or when doing continuous two-

stagecementing a pump down opening plug is used nstead of a gravity-

driven openingbomb.

Liner Cementing

A liner is defined as a string of pipe which doesnot extend o the wellhead. Liners

are used o case-offbelow an existingcasing string. Liners are of three ypes.

Drilling liners areused opermitdeeper rilling by isolatinga sectionof the

holewhichpresents difficult drillingenvironment,.e., ost circulation,

overpressurcdnterval, loughing r plastic ormations.

Productioninersareusedor thesame urposes sproduction asing, nd

in a deepwell the useof aliner can csult n significantsavingsn steel.

Snrb inersextend rom the top of a liner to apointuphole nsideanother

stringof casingor liner. A stub iner s used o isolateworn or damaged

tubularsor to provideadditionalprotectionagainstcorrosionand/or

excessiveressure. possible equencef linersn a deepweli is shown

by Figure20, rom Reference 3.

o

o

o

5 8



Figure20

Example of casing and liner program to seal of t highpressure zonei in a deep

-well(afier Mahoney and Barrios)."'

Thesuccessfulunningandcementingf a iner canbe oneof themostchallenging

operarionsn the oil field. Thereare severaleasonsor this. Productioninersare

oftensetat greatdepthunderconditionsof elevatedemperaturesndpressures.

Usually hemostcriticalregronor establishmentf anannularseal or production

casingcements in theviciniry of the casingshoe; or mostproductioniners he

shoeand he ap (topandbonom)arebothcriticalregions.Typically, heannular

clearanceor a liner s very small. A drilling liner s usually equiredbecausef

somekind of hole problem,which can alsomake effectivecementingmore

difficult

ll I sunmcE r--r--

lll-cesrrc

l l llf=#i?$" VPRE''URE

I r lt \| \

(iloRrAL)

I INTERMEDIATE I

y'z cesnaI

| | FRA. PREssuRE

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i l - \ " \lF..'*n.,n'*"'..ll t'=."o"* ( i

fl-srueu$tER reeronmu\

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5 9



LinerEquipment

A typical array of liner cementingequipment s shownby Figure 21, which wastaken rom

Reference 6.

Liners arenormally run on drill pipe which usuallyhas smaller .d. than he liner. Because

of this only a top cementwiper plug is used. The wiper plug is loaded nto the top of the

liner as the liner is being run; the liner cementingplug has a hollow center and it is

equippedat its lower endwith a seatingshoulder. After the cementslurry hasbeenmixed

ar rhesurfaceand s in the drill pipeapump-downplug is launchedwhich passeshrough

the drill pipe, seats n the wiper plug and the combinationplug thenperforms he usual

function of a top wiper plug including seating n a landing collar in thevicinity of the float.

A liner may be seton bottom, but buckling is inevitable and the resultingwall contact

makes a difficult mud displacementproblem even more difficult. For this reasona

mechanical set (using reciprocationand/or rotation) or hydraulic set (utilizing pump

pressure) iner hangerequippedwith slips s usuailyemployed. It is important to centralize

the iner; bow-springcentralizersmay be used n the openhole if there s sufficient annular

clearance. zugtd centralizersare used n the casing/liner ap region, and also in the open

hole in casesof very narrow annularclearances.The length of the ap can be as ittle as50

feet for a drilling liner or asmuch as 500 feet for a production liner. Maximum length of

lap is used f there s gasnear he top of the iner, i.e., near he shoeof thecasing string.

The Ooeration

Becauseof narow annularclearance, ong liners should be run slowly to reduce the

tendency o fracture he formationwith surgepressure.Running speeds f 2-3 minutes or

eachstandof drill pipeare cornmon.

Even thoughachievingadequate isplacement f drilling mud is essentialo a successfui

liner cementingoperation, iners arenot usuallymoved during liner cementing. They can

be and should be moved. Kolthoff and Scales 24)reported a significant improvement n

cementingsuccessn 210 Sohio Alaska PetroleumCompanywells at PrudhoeBay by

changing rom a 9 5/8" productioncasingcompletion n 10,000 t MD deviatedwells (hole

anglesup to 67") to a 7" production iner completion. The improvement n cementing

success asattributed o the acts hat10,800' f 9 5/8" casing ouldnotbereciprocatedn

most of thesewells, and 1500 eetof 7" liner in the 8 L/2" hole drilled below the 9 5/8"

casingshoe could be. To permit reciprocation a hydraulic set liner hangerwas used. The

6 0



M I X I N G D I S P L A C I N G

\J-7

Figure 1

LinerCementing

DISPLACING EN DO F O B

6 1



liners were reciprocated hroughone 30 ft cycle per minutewhile pumping preflush(water

in most instances)and cementslurry. After the liner wiper plug seated, he liner hanger

was serhydraulically by pressuringup. When the 8 L/2" hole was drilled, sufficient

rathoiewasprovided so f the iner stuckat the top of theupstroke, he iner shoewould be

at the desiredTD or below.

Liners can also be rotatedby the useof a mechanicalset iner hanger which is equipped

with a clutch thar s engagedby additional otation after setting. The running string is then

panially disengaged nd he iner is rotatedusinga splinedrive equippedwith bearings 2s).

The importanceof liner centralization n achievingadequate isplacementof drilling mud

has beendiscussed. Centralization s alsoneeded o reduce he probability of differentiai

stickingof thepipe while runningand/or eciprocating he iner.

Someoperators se sufficientslurry to cement he openhole, and he ap regionwith 25-

45Voexcess nd then cleanup by reversecirculation atier stinging the drill pipe out of the

liner hanger. During the reversecirculation procedure, he friction pressuredrop resulting

from thererurn luid flow up the small diameterdri_ll ipe is reflectedon the ust placed

cement slurry. To avoid forcing the slurry down the hole away from the liner lap as a

result of rhis pressure,eversingout shouldbe done slowly andcarefully, f at all. Other

operatorsuse only about 80Vo f the slurry required o fill theannularvolume thenperform

a plannedsqueeze f the lap. It is preferred o employ the first technique cementbothannuli with someexcess)and then ater squeezehe ap, if necessary.The reasons hat the

plannedsqueezeechnique s not preferred s that the success f liner cementingoperations

has mproved n recentyears;Kolthoff and Scales 24)rcportedzero ailures or wells where

the linerswere niciprocatedduring the entire time preflushandcementslurry were flowing

in the annuli. Also, the plannedsqueezeechnique nevitabiy leavessomeuncemented

annulus which can be difficult to accessshould subsequent emedial operationsbe

required.

Liner CementingSlurries

Since hevolume of cementslurryrequired o cement iners s relatively small,batchslurry

mixers may be used. Batchmix slurriescan be more uniform than slurriesmixed using a

jet mixer or RCM.

Liner cementing slurriesrequire fluid loss additivesto control the extent of cement filter

cake build-up in the typically nilrow annulus. It is not uncommon o cementa 5" OD liner

6 2



H .

below7" casing nsidea 6 U2" drilled hole; theresultingannularclearances only 9116"

Problems that are sometimesattributed to premature set of the cement during liner

cementingareusuallybridgrngof cement ilter cake n the annulus.A cementslurry having

API HT/FIP 30-minute luid lossrate of 50-100ML is suitable or liner cementing.

The most difficult slurry design problem for a cement ntended for a long liner at great

depth s to incorporatesufficient thickening time to place he cementandreversecirculate

any excesscementslurry from the well. Sticking the drill pipe in a deepwell is a cardinal

sin, yet the cement should not be over retarded, which would result in undue delay in

snengthdevelopmentof the cement eft in the ap region (which can be >100"Fcooler than

the shoe). The only solutionto this problem s careful pre-job laboratory estingusing

realistic BHCTs and BHST's. To addresshe strengthdevelopmentat the top of the liner

problem, t has been eportedby some nvestigators hatcuring pressures igher than 3000

psi (standard or the API compressivestrength ests)hastens he onsetof measurable

srrengrh. If a laboratorydoing slurry design or a long, deep iner has he capabilityof

curing compressivestrengthspecimensat pressures n excessof 3000 psi, pressures

correspondingo actualhydrostaticat the op of the iner can be employed.

CementEvaluation

The functionsof a primarycementsheathare o seal he annulusandprovide mechanical

supporr o rhe casing. Ideally, evaluationmethodswould providea directmeasure f the

performanceof these unctions,but actuallymostof the evaluation oolsand techniques re

more or less indirecr

1. Indirect Indications

A cement-top emperature urvey(describedn the cementchemisury ection)used

in conjunctionwith annularvolume calculated rom an open-holecaliper og, taken

before casing was run, can provide some indication of mud displacementefficiency. For example, if the primary cementing job were conducted with

essenrially ull retums andthe ndicated ength of theprimary cementcolumn is 15-

ZAVo nger than calculated,t canbe assumedhat a substantial mountof mud was

bypassed.

The cement bond log (CBL) is widely used to provide a measureof cement

coveragen the annulus. The CBL is an electro-acoustic evicewhich provides

6 3



threeseparatemeasurements:signal travel time, casing signalamplitudeand total

energydisplay. The travel time measurements used o assure hat the casing

amplitude signal s accurate, .e., it is an indicator of tool centralization. The total

energydisplay s used o definecoupling to theformationand t alsoprovidesother

detail with regard to annular coverage, .e., if the collars are not bonded,

characteristic "'W" signanrresare found within the total energy display. Casing

signalamplitude s a measure f the attenuationof the acousticsignal,which varies

directly with the bonding of the casingby the cement sheath. Fitzgerald, s1a| (26)

have developeda methodof using he nformation from the casingamplitudecurve

to calculateannular ill of cement,which in turn can be used o estimate he zone

isolation achievedby cementedcasing of a given size. An example of this

calculation s shownby Figure zl.L Q6).

Figure 1.1

According to information found in Reference26, l0 feet of 7" casingwith 807o

cement s sufficient o isolatezones; argercasing equires onger cementedntervals

to achieve solation. It is evident that the CBL providesconsiderablenformation,

I Ctrcx?

6 4

a

o

ta

llat:at

a

a

I



2 "

but it must be consideredan indirect cementevaluation ool, as t doesnot address

annularhydraulic seal directly.

More Direct Indications

More direct cementevaluationmethodsactuaily monitor flow behind pipe by

measuring emperature r noiseanomalies singappropriate ased-holeogs.

When unwantedgasentersa cementedannulus herewill be a cooling anomalyat

the point of entry due to expansionof thegas. As the gas moves uphole,a heating

anomalywill beobservedas he geothermally-heated as rom downholemoves o

cooler portions of wellbore. Unwantedwater normally moves downhole after

enteringa cementedannulus, esulting n a cooling anomalymoving down. A

radial differcntial temperatureRDT) tool has beendevelopedby Cooke (22).This

tool utilizes eitherone or two temperanresensorsn the samehorizontalplane. In

use he tool is positioned n thecasingat the elevationof the suspected nwanted

flow androtated. Logs takenusing his tool provide nformationregardingboth the

presence or absence) f unwanted low and the location(depthand azimuth)of

unwanted low. The laner nformation s useful n repairing he well.

#ut i l i zesasensi t ivemicrophoneusedinconjunct ionwi th

amplificationandotherelectronics. f thebackground oise evel s low, i.e., withthewell shut-in, he noise ogging ool can"hear"the enuryof unwanted luid into

the wellbore. Flow of gas s more easilydetected hanflow of water.

Definitive Indications

Statedbriefly, if a cementob accomplisheshe ntendedpurpose, t is considered

successful.The ntendedpurpose f a cementob includeprotectionof the casing,

pressure ontainment,andachievingdesiredproduction or injection) panerns.

For the cementsheath o protectthe casing rom external casingcorrosion it must

reachsufficient elevation n the annulus o coveranypotentially corrosiveaquifers.

The ocation of the top of cementcan be established singa cement-lop emperature

log or CBL.

Fotlowing thecemenringof surfaceand ntermediate asinga pressurentegrity test

(PIT) of the casingshoe s usuallyconducted.Procedures to drill the float and the

3 .

6 5



shoeplus a small amount of additional hole. Sufficient surfacepressure s then

applied so the pressureat the shoe s at least equal to the maximum hydrostatic

pressureexpected o be mposedon the shoebeforethe next casingstring is set. If

the requiredpressures reached,drilling proceeds. f the required surfacepressure

cannotbeanained, he shoemust berepairedby squeeze ementing.

After perforationshavebeensealedby squeeze ementing, heymay be testedusing

formation pressure.This is accomplishedby swabbing luid from the well bore so

formation pressurewill be imposed across he squeezedperforations. If one or

more of the perforationshad beenplugged with mud or other well bore fluid, the

plug will be expelled,andthe squeeze ementingoperationcan berepeated.

The most definitive tesr of the primary cementing of a production well is a

production est. If thewell produces he expected luid(s) at anticipated ates, t can

be assumed hat the primary cement ob is successful. If the above described

conditions arenot met, someof the diagnosticproceduresust describedshouldbe

applied so a decisioncan be made as to whether or not squeeze ementing s

needed.

The primary cementingof an injection well is consideredsuccessful,f the njected

fluids are confined to the intended arget nterval. Diagnostic techniquesused o

verify that such s the case nclude temperature ndradioactive surveys.

"Slugs"

ofshorthalf-life gamma ay emitting isotopescan be included n someof the njected

fluid and a gamma-ray og canthen berun. If anopen-hole,naturalgamma-ray og

is available or thewell, it can aid n interpretationof the og describedabove.

AnnularGasFlow Mitieation

Annular GasFlow (AGF) can be defined as gasor gas pressureat the surfacesome ime

afterprimary cementing. AGF canalsooccurdownholeas nterzonal low; this type flow

can bedetectedusinga noiseor temperatureog. Most often AGF is observed 2-I6 hours

aftertheprimary cementingoperation; t hasbeenobservedmuch earlier(assoonas he top

wiper plug bumped)or much ater(daysaftertheprimary ob).

AGF is a costly and evendangerousproblem. It can lead to safetyhazards or both men

and material. Repair (by squeeze ementing) s difficult and costly. The most serious

economic mpact can be oss of reserves.

I .

6 6



Il . Reasonsor Occurrence f AGF

Cementstarts he settingprocesswith theformationof a gel coating on the cement

grainsas soonas heyarecontacted y water(seeFigure2). As a consequencef

this, the cementslurry developshigh gel strengthwhen quiescent. During this

same nitial settingperiod thecementundergoes omeshrinkage; t later rebounds

and eventually shows some volume expansion. The early time shrinkage s

illustratedby Figr.rre 2,which was taken rom Reference28.

Figne22

L r g r n dr ! l t c ! r t x t

!:.-r-1!:.-._ |

l 2 r f

TIME N HOURS-€amad thnn€€a ddrogd|.rn t 7CC.

The data of Figure 22 representcombined nternai and externalvolume changes.

External volume shrinkage s 1.5-2.07oor most cements. Because he cement

slurry is alsoundergoinggellation, t cannotslumpto compensateor the shrinkage

andfull hydrostaticpressureof thefluid column is not transmitted o the bottomof

the hole. This allows gas to enter the annulus. Cooke, sg al (29), made

measgrements f annular emperature ndpressuren sevengaswells by attaching

sensorso theexteriorof thecasingat differentelevations.Data were ransmined to

the surfaceusinga logging cable,which was aisoattached o the exteriorof the

casing. The pressure nd temperaturemeasurements eremadewhile the casing

was beingrun, the mud/holeconditioned, he cementpumped and until thecement

l - ?-I|9 .

cuo

= .ttlct

I

=E t-o(,

E rFIl

I l

=Jo

2a

6 7



attainednitial set.Thedata rom onewell is shownn Figure23whichwas aken

fromReference29.

Figure23

th

6 6zo? 5U

. . 4cc

@

g 3

a

2

* ^; m5 r8o

S 16{)ul

3 140F 120

SENSORNO.DEPTFI FTI IRKBI

l(m ll m 1200TIME. MINUTES

2 3 46909 5488 4787

lan 1rm

5 6463:1 3txl6

cp

1ctstl

Annular gressure and tomperature-

Well A

It is apparenrrom Figure 23 that the hy&ostatic pressurestarteddropping as soon

as he top plug seated;heprcssure ecordedat eachsensoreventuallydropped o a

valuebelow the equivalentmud weight (EMW) required o preventgas nflux. It is

also of interest o consider he annular emperaturc uwes. The inflection point in

each emperature urye (occurringabout 1000minutesafter the first joint of casing

was run into the well) representshe principal exothennof the cement; t occurs

when the cementachievesnitiai set. In the sevenwell program t wasobserved

that the wells, which did not show AGF were those ndicating this principal

exothennat about he same ime or beforethe annularpressuredroppedbelow the

EMW needed o control gas. In other words, do re! over retard the cementused

for a gaswell. If gasenters he annuluswhile the cementhas ittle or no strength

andhigh permeability, t flows upward and expands.As a result, the cementsheath

is renderedpermanentlydefective. High cement slurry filtration rate makes a bad

situation worse in that loss of water from the cement slurry resuits in more

shrinkageandmore gellation. In extremecases f high fluid lossa cement ilter

=

oul(9

6 8



2 .

cake"packer" can form in the annulus and make transmission of hydrostatic

pressurempossible.

Anothermechanism orAGF is related o theoccurence of freewater from a slurry

used to cementa deviatedwell. In sucha well free water will migrate to the top

side of the hole (usually one foot or less n a deviatedwell) and form a coherent

uncemenred hannel for the entire length of the cementsheath.WebsterandEckerd

(30)conducteda laboratorystudyutilizing inclined modelswhich indicated hat gas

readily flowed through free water channels.

Preventionof AGF

A variety of materialsand methodshas beenconsideredand tried in the attempt o

solve the AGF problem. Thesematerialsand methodsare discussedbelow goingfrom least successfulo most successful.

In an attempt o increasehydrostaticpressuredownhole, weighted cementmix

water hasbeen ried. Cooke,et al(29) ound that the hydrostaticpressure ownhole

can fall to values ower thanwould be exertedby a columnof mix water,regardless

of mix warer densiry. This behavior s illustratedby Figure 24 ftom Reference29.

Figpre24

SENSORDEPTHS.FEET

PINGCOMPLETED

4e. 1326

2 3

TIME HUNDREDS FMINUTES

6 4G

ozv,

oF 2;E

A 1oUJEG

130

s 120' . 1 1 0

o,E 100

H s o80

EMW= .5LB/GAL

6 9



The usualmethodof increasinghe densityof the mix waterwasby dissolving

NaCl in themix water. Sincehigh concentrationsf NaCl retard he setof

cement;hisapproachanbecounterproductiveecausef over etardation f the

cement.

Mechanical ibrationof thecasing o break hegelstructurcof thecementslurry n

theannulus asbeenevaluatedn thelaboratory nd n the ield. It was ound hat

vibrationof anythingother hanshortcasingstrings approximately 000 1200

feet)wasbothexpensivenddiffrcult. This approach asnot alwayseffective;he

need s to vibrate hecementnot the casing.The timingof the operations very

critical; if vibration s attempted fterthe cementhasstartedo bond he casing,

vibrationwill becounterproductive.

Gas-generatingdditives avebeenused orenderhecement lurrycompressible.Although somesuccessesavebeencitedfor this approach,herehave been

problems. To be effectivehegasmustbe generated hen hepumpingof the

slurry s stopped not roo ong beforeor after. Timing of the gasgenerations

somerimesifficult to achieve.Becauseydrogens thegaswhich s generated

therehas beensomeconcern egarding afety,particularlywhen appreciable

volumesof hydrogenhave beenproduced o the surface. The most serious

reservationsoncerninghis process ave beenexpressedy thosewho have

measured ressuresownhole ollowing thepumpingof compressibleement

slurries nd oundno mprovementn the ransmissionf hydrcstatic ressure.

Successesavebeen iled€8) n prcventing GF for cement lurries ontaining n

additivewhich cduceshecement ermeabilityovery owvalueswhile hecement

is liquid, n transitionanda setsolid. Otheradvantagesited or thisadditiveare

lessshrinkageseeFigure22),low filtration rate andbetterbonding. The D-S

(Dowell-Schlumberger)esignationor thisadditives D 600.

Historically,gleatest uccess€sn preventingAGF hasbeenby the useof what

refer o as he"conventionalapproach".Manyof the eatures f this approach re

applicableo anyprimarycementob andwill achieve ptimum esults,whethergas

is apotentialproblemor not. The elements f the"conventionalapproach" reas

follows:

7 0



o The casing sedn a gas-prone ell shouldnot becoatedwith mill varnish.

The deleterious ffectof mill varnishon bonding s shownby thedataof

TableVItr, whichwas akenromReference8.

TableMtr

BondingProperties f VariousPipeFinishes

Cement: PIClassAwaler content:5.2 gal/sackCuring emperature:0oFCuring ime:24 hoursCasing ize:2 in. nside an.

EondStrength

Type of FinishHydraulic

(psig)

Ste€lPipeNew (mill varnish) 74New (varnishchemically

removecl) 104New (sandblasted) 123

Used (rusty) 141New (sandblasted, esin-

sand coated) 2,4ooPlasticPioe

Filamentwound (smooth) 79(rough) 99

Centrilugally ast (smooth) 81(rough) 101

Sincedisplacementf drillingmud rom hole rregularitiess very difficult,

the attempt houldbemade o drill a uniformhole. In somewells thiscan

bebestachievedy drillingmudchemistry.t t4''r

During hecementob, bestpossiblemuddisplacementractices houldbe

employed.This includescontrolof drilling mud properties o minimize

fluid lossrate and ime dependent el strengthand he useof a preflush.

The preflushandcementslurryshouldbe pumpedas fast as possible,

without nducing oss of returns. The pipe shouldbe cennalizedand

moved.

The cement lurryusedn agirs-prone ell mustnot beover etarded; hort

transition ime s needed.Thc 30-minute{T/HP API fluid loss ate(tested

accordingo AppendixF of Reference2)houldbe n the 50-100ml range.

For a deviatedgas-prone ell, freewateroccuTence houldbe as ow as

possible.Freewatermeasurementshouldbemadeaccordingo theAPI

operatingreewater est AppendixM of Reference); acceptablemounts

are n therange f 0-2.5ml. If a slurry s designed ccordingo Section

Gas(psig)

Shear(psi)

200 ro 250 15

300 to 400 70500 to 700 150500 to 700 150

r ,100 o 1,200 400+

2102702203 1 0

o

o

o

7 L



II.E. of this extand reewater breakout"is excessivetested ccordingo

AppendixM),1-2Vo bwc)bentoniteanbeaddedo thedry blendwith no

correspondingncreasen mix water. Used n this way the bentonites

functioningas a chemicalblotter"and heresultingslurrywill probably

haveacceptableropemies.

Pumppressurerom the surfaceapplied o the annuluscan be effective.

The amountof permittedpump pressure s limited by lost circulation

considerations.Pressurc houldbeapplied mmediatelyafterthetop wiper

plug is bumpedandmaintained ntil after the principalexothermof the

cementhasdeveloped;t will befound hat he afiiountpumped s usually

about .S%o f the cementvolume. Cooke,st al (29)verified that surface

annularpressureanbe ransmitted ownhole.Figure25 was aken rom

Reference9; theanowson the abscissatimescale)ndicatewhensurfacepressurc asapplied.

Figure25

1m0

100

Annular pressure and temperatute - Well I

RemedialCementing

Remedialcementing s informally definedas a well cementingoperation hat s not primary

cementing. Remedialcementing s used or repair (bothof tubularsand theprimary cement

o

smo

E**u,l

$ amov,U'

Hzomo

0

r. 2fi)

= 150z,u,l

ry.

1 5 1 6 1 7 1 8 1 9HUNDREDS F MINUTES

7 2



sheath)abandonment,estingandconnol of theproductionpatternof a well. Two typesof

remedialcementingarediscussedn thischapten plug cementingandsqueeze ementing.

A. PlueCementine

A cementplug s a columnof cementplacedeither n casingor in the openhole.

The first recorded seof a cement lurry n anoil well was he dumpingof a 50-

sackplug in a well in theLompoc ield in California n 1903 o successfullyhut

off down-hsl6wx1s1l).

Describedn subsequentartsof this sectionwill be the scope uses)or plug

cementing,echniquesmaterials ndmethods), ndproblems ncountered hile

performing lugcementing.

l. Scope f PlueCementing

Zone solation

Seninga cement lug s a common ndcosteffectivemeans f isolating

zones.The ntentof theoperationmaybe to shutoff water, ecomplete

higher or lowerby drilling through heplug),or to protecta low pressure

zonebeforeperforming squeezeob or hydraulicracturing perationSee

Figure26).

Figrre26

(FromReference1)

CementPlug or Zone solation



Testine

The useof cementplugs n the testingof an explorationwell is a specific

exampleof the useof this cementing echnique o achievezone solation.

Expendableexploration wells are often cased hen potentially productive

zonesare ested rom thebottom up. After testingan nterval a cementplug

is placedover the perforationsand the well is, in essence, lugged and

abandoned s t is tested.

Lost CirculationControl

When drilling-fluid circulation is lost during drilling, it is sometimes

possible o restorecirculation by spottinga cementplug across he lost

circulation zoneand hen drilling through heplug after the cementhas been

allowed to set. Although someof the cementslurry may be lost to the

formation, i.e., the thief zone, after the cement sets it will aid in

consolidating he ormation. (SeeFigure26.I). Lost-circulationadditives

are often included in lost-circulation cementplugs and, dependingon the

natureof the lost-circulationproblem, he density of the cementslurry may

bereduced.

DirectionalDrillin g and Sidetrackin

A plug of this type (often referred o as a whipstockplug) may be set n

casingor openhole (seeFigure27). Theseplugsare used o aid n drilling

aroundunrecoverable ish or to aid in deviating the wellbore to reach the

desiredgeologicobjective. The success f a whipstockplug depends n

high compressivestrength; his requirement, n turn, placesa premium on

avoidingcontaminationof the cementandproperslurry design.

PlueandAbandonG andA)

It is inevitable n the ife of anywell (dry hole or depleted roducingwell)

thatcementplugswill be used o close he well completely . Cementplugs

help preventzonal communicationandmigrationof any fluids that could

contaminate underground fresh water sources. The requirementsof

7 4



2 .

regulatory bodies concerning

consulted SeeFigpre28).

Plug Cementine echniaues

BalancedPlueMethod

plugging and abandoningwell should be

This is usually the method of choice; t is simple, requiring no specialized

equipment,and any engthplug desiredcanbeplacedusingthis technique.

Figure 6.1

GromReference6)

Cement lug or Lost CirculationControl

Figure27

(FromReference1)

Whipstock lug

ffj=:-'--=--=.-:------ -_::-:-:

7 5



To calculate he ength of a balanced lug, the following relationshipmay be

used:

N = cu. ft. of cementslurry

h = lengthof balanced ementcolumn

C = cu. ft. per linear foot of spacebetween ubing

(or drill pipe) and casing(or hole)

T = cu. ft. per linear ft. of insidevolume of tubing

(or drill pipe)

Exampleproblem: Calculate he ength of a balancedplug providedby 100

sacksof nearClassA cementplaced hrough6.4lblft, 2-7 9-inch ubing to

the bottomof a 3500 ft. well casedwith 7-inch, 26 Lblft casing. Also,

calculatehevoiume of displacementluid required o balanceheplug and

the elevationof the top of the plug after the 2-7|8-tnch ubing hasbeen

withdrawn.

1. Calculatehe cu. ft. of cementslurry(N): According o pageF-55 of the BJ

DecimalBook (32),ClassA cementmixedwith 5.19gallonsof waterper

sackof cementyields 1.17cu. ft. of slurry, hen

100 ks l.L1cu. t. = 117 u. tsk

2. The length(h) of the balanced lug is calculated rom

N = 117 u. t. (fromcalculationabove)

C = 0.1697 u. t.Aineart.

(p.C-18of Reference4)

T = 0.0325 u. t.Aineart.

h= N ,whe reC + T

h= N ,whe reC + T

7 7



(p.A-7of Reference2)

117 cu ft. 117cu . f t . - ('7(l 6^^+

0.2022+r6n . o.o32s+

3 . The volume of displacementluid required o balance he plug can be

calculated y: 3500' 579'=2921'(topof thebalanced lug); he capacity

of 6.4\blf\2-7lS-inchnrbings 0.0058bblVft.(p.A-7 of Reference 2)

2921ftx 0.0058 bls/fr= 16.9bbls

Thecalculation f the opof theplugafter he ubing s withdrawn ollows.

The inear t./cu. t. of 26lbs, 7-inchcasings givenas4.6549 t./cu. t.

(p.A-10 of Reference2)and

117cu. t. (1.,abovc) 6549 t./cu. t. = 545'and

3500 ' - 45 '=2955 ' .

This informationcan be used o determinehe lengthof 2'7/8" tubingto be

withdrawnbeforeeverse irculatingo cleanup, .e.,545 t. of tubing.

DumpBailerMethod

For the dumpbailermethodhe cementslurry s conveyedo the desireddepth n a

durnpbailerrun on wireline. The ccments dumpedby opening he bonomeither

with a squibcharge r by repnringa bottomdisk by sening own. Thismethods

normallyusedn low pressureased olesat shallowdepth,although ement lugs

havebeenserasdeepas12,000eet with a dumpbailerby using etarded ement

slurries. f a cement lug sdumped ff bottom,a imit plug,cement asket, ridge

plug or sandpackcan beusedat the bottomofthe desiredplugging ocation o

preventmigrationof theplug (SeeFigurc30). As advantages,hismethodoffers

goodcontrolof plug settingdepthand t is relatively nexpensive. ts principal

limitation s the smallvolumeof cement lurrythatcanbe dumpedn asinglebailer

run.

4 .

7 8



Figure30

(FromReference3)

DurnpBailerMethod

WIRELINE

DUMP BAILER

ELECTRICALMECHANICAL

DUMP RELEASE

7 9



J .

The Two-Plug Method

The nno-plugmethd utilizes a plug aboveand below the cementslurry, and a

wiper plug catcher n the bottom of the driil pipe (or tubing). The bottom plug

precedes he cementslurry cleaning he drill pipe (or tubing) and isolating the

cementslurry from the wellbore fluid (SeeFigure 31). When the bottom plug

reacheshe catcher, t is pumpedout into the wellbore. The cementslurry is placed

at rhe desired ocation in the well and the top plug seatsand seals he top of the

catcherassembly; his event is signalledby an increase n surfacepressure. The

work string is then pulled up so the lower end of the tail pipe is at the calculated

depthof the top of thecementplug. Additional pressurecausesa sliding sleeve o

open a flow path through the plug catcher o the boreof the work string, allowing

the work string to be cleanedby reverse circulation.

The two-plug system s particularly suited o placing plugs at substantialdepth

where displacementvolumes are difficult to calculate, and the opportunity for

contaminationof thecementby wellbore fluids is great. The obviousadvantage f

this technique s to enableprecise ocation of anuncontaminated ementplug. The

obviousdisadvantagesrecomplexityand expense.Top and bottomwiper plugs

aresometimes sed n open-ended ipe in conjunctionwith the balanced ement

plug techniqueo mitigate he contamination roblem. [n this"modified'balanced

plug method, he wiperplugsarepumpedout of thework stringandremain n thecementplug.

It shouldbe observed hat although heproblemsdiscussedn the following section

(migration, contamination,andcement sturry design)are nterrelated, hey will be

addressedn separateub-sections.

Misation

If a cementplug is placed off-bonom and if the cement slurry density is

substantiallydifferent from that of the wellbore fluid, the cementplug will move

before setoccurs. The plug cementslurry is usuallyheavier han the wellbore fluid

(water,hydrocarbons, nd/ormud), and he tendency or thecementslurry to move

can beminimized f the slurry density s reduced-Cementslurrydensity eduction

8 0



Figure 1

from Reference6)

Tell-TaleCatcher ubOperation

1 - RUNNINGN2 - BOTTOMPLUG ANDED3 - CLE.ANINGFALUMINIUM AILPIPE. - TOPPLUG ANDED

5 - REVEFSE IRCULATIONND PULLING UT

8 1



is usually accomplishedby usingan additivethatpermits the useof a high water to

solidsratio. A low densityslurry of this type develops ower compressivestrength

than a corresponding eat slurry; this s anadvantagen a lost-circulationplug and a

disadvantage n other cement plugs. Also, as noted in the following

"contamination"

section, he compressivetrengthdevelopmentof a high water

ratio cement slurry is more sensitive to contamination. It has been reported by

Smith, s1al.,€4) harhigherviscosity cementslurriesaremore likely to establisha

stable nterface with mud and are lessprone to miglate. A paper by Beirute (35)

describesa computation method that can be usedto define the cementrheology

desiredto maintain a stablemud,/cementnterface. The interface betweenmany

muds and cements shows a natural tendency toward gellation; this behavior is

beneficial n this application.

A cementplug that is stable nitially (as t is being deposited) s more likely to

remain stable han a plug depositedunderunstableconditions s to becomestable.

Unfortunately, the conventional echnique or depositinga balancedplug leads o

initial instability. The cement slurry exits the work string moving in a vertical

downward direction, then it must undergoa complete eversal n direction of flow

and move vertically upward into the annulus. The oppornrnities for mixing of

cementslurry and wellbore fluids, as well ascontinueddownward movement,of

the cementslurry areobvious. Smith, et. al., (34)reported mprovement n cement

plug stabiliry n both aboratoryexperiments nd n thefield by useof a diverter tool(seeFigure 32). This tool assurcshat initial flow of cement slurry from the work

string will be horizontal, insteadof verticai and downward. In its simplest form,

the divertertool is a bull-pluggedwork stringwith enoughholesdrilled in the ower

endof work stringsothat the availablearea or flow will be equal o that of the bore

of the work string.

Contamination

There s always hepotential or contaminationof the cementslurry by the wellbore

fluids in any plugging operation. A relatively small volume of cement slurry is

placed n a large volume of potentially contaminating luid, and displacement

mechanicsare less favorable for plug cementing than for primary cementing.

Contamination f a cementplug canbe of two types: in a plug placedoff bottom

substantial eplacement f the cementslurry by the residentwellbore fluids can

occur (this s related o themigrationproblem),or the cementslurry canmix with

8 2



Figure32

(FromRefercnce4)

DiverterTool

4 HolesPhased 5"

4 Holes

Bull Pfug

the wellbore luids. The deleterious ffecton cementcompressive trengthby

mixingwith mud s illustrated npage47'48byTableVtr fromReference8.

Referringo TableVII cementB is more csistanto contaminationhancementA

becausef its highercemento water ationot because f slurrydensity,per se,

(increasing lurry densityby the useof weightingmaterial s actually counter

productive n thisr€gard).

8 3



o

Some measures which minimize mud contamination of cement plugs are

summarizedbelow:

Placeopen-holecementplugs n gaugesectionof thehole, f possible.

Condition the mud prior to cementing. Centralize he work string. Rotate

the work stringwhile displacingwith cement,when cementdisplacements

complete,stoppipe movemenl

Wiper plugscanbe usedaheadof and behind he cementsiurry.

Do not use over-watered ementslurries. Use either specifiedwater to

solids atio or less han specifiedwater to solids atio.

Batchmix the cemcntslurry.

Use flush aheadof and behind he cement.

When acemenrplug is depositedusing hebalancedplug technique,a flush is often

usedaheadof and behind the cementslurry, unless he wellbore fluid is water or

low-density, ightly-treatedwater basemud. Water is the flush of choiceunless

more fluid density is required and/or the wellbore fluid is oil-basedmud. In the

latter nstance oil-basedmud), a compatible, ormulated lush, .e., BJ's MCS-2,

is often used. The volumes of the post-andpre-flushes,must be selectedso the

pre-flush will reach the sameelevation n casing/work string annulusas the post-

flush n thework string,whentheplug is balanced.For example, eferring o the

problem found in the balanced lug section, f a 10 bbl waterpre-flush had been

used, he engthof thepre-flush n the 2-7l8-inch ubingx 7-inch casingannulus

above hebalanced ementplug would be

10bblsx 33.0761 = 331 t., (p.c-18, f Reference2)

and to balance,what volume of waterpost-flush wouid berequired? The capacity

of 6.4 lbs/ft of 2-7|8-inch ubing is given on p. A-7 of Reference32 as 0.0058

_t_bbl

8 4



bbls/ft.,and

331 r x 0.0058 bls/ft= 1.9bbls.

SlurryDesien

The basicsof slurry designwere covered n detail in a precedingchapter. With

specific cferenceo plugcementing, lurrydesignshouldstartwith a neatcement

mixed using the specifiedamountof water. Cementslurry propertiesare then

varieddepending n the rcquirementsf the specificoperation.

Thickeningime of aplugcementing lurryshouldbeadjusted, singaretarder r

acceleratonf needed,o estimatedob time plus 30 minutes. Over-retardation

shouldbeavoidedas he slurry s susceptibleo migntion andcontaminationwhen

it is in afluid state.The hickcning ime testused o establishetarder r accelerator

requirementshouldsimulate he pressure nd temperameenvironmentof the

acnralob ascloselyaspossible.

Both the compressivetrengthandslurrydensityof a lostcirculationplugareoften

reduced-Bothof these lurrymodifications anbe accomplished,imultaneously,

by the use of a high wat€r requirement dditive suchas bentoniteor sodium

metasilicate@J'sThrifty mix).

The compressivetrength f a whipstock/sidetrackinglug shouldbe ashigh as

possible. The preferrcd echniqueor increasing ementcompressive trength

beyondhatdevelopedy neat em€nts by addinga dispenant,.e., BJ'sD-31. A

dispersantsedat concentrationsf about0.75percentbwc)permits he slurry o

bemixed at ower wate,ro cementatios han s possiblewith neatcement.The

effectof thison cement ompersive trength anbeseenby referenceo TableVtr.

Reducinghewater o csmentatio alsohas he effectof incleasing lurrydensity;

thismay be an advantage r disadvantageepending n the application. Smith,et

al., (34)recourmendhat a dispersantnot be used o lower the consistency

(viscosity, ieldpoint,etc.)of a cement lurry,which would occur f a dispenant

were used n the absence f a reduction n water o cement atio. Statedmore

generally,ow viscosityslurriesarenot rccommendedor any cementplugging

operation. On occasion,5-20%obwc) frac sandhasbeenadded o cement o"toughentheplug". There s no evidencelaboratoryr field) thatanydiluent frac

8 5



sand,weight material,etc.)doesanything o the setcementexcept o lower the

compressivetrength, hich s undesirableor a whipstock lug.

4. Conclusions

Cementplugsprovidea simple,costeffectivemeans f performinga varietyof

drilling andcompletion perations.

Threegeneralechniquesbalanced lug,dump bailerand wo-plugmethod)are

used or placingcementplugs. Each has advantagesnd disadvantagesor a

particularapplication.

Theprincipalproblems ncounteredn plugcementing remigration,contamination

and mproperslurrydesign.Eachof these s addressedn the ext

B. Squeeze ementing

Squeezeementingnvolvespumpingcementslurry throughan opening nto a

target oid. Theopenings usuallyaperforation, ut t canbea splitor corrosion

hole n casingand t canbea fracturen the ormationor primarycement heath.n

mostsqueezeementing perations,hecementilter cake orms he nitial seal, o

squeezeement lurry iluation behaviorsvery

mportant.

1. Scoge f Squeezeementing

Squeezeementings usedor:

o Repairof a primarycement heath hathas channeled,.e., by-

passedmud.

o Augmentationf cement ps.

o Elimination or rcductionof water or gas ntrusion into an oil-

producingnterval.

o Repairofdamagedasing.

8 6



o

o

Plugging onesn an njectionwell that arenot ntended o receive

injectionluids.

Pluggingand abandonmentP&A) of depletedor watered-out

producingntervals.

Soueezeementingechniques

Squeezeementingechniquesreclassified ccordingo how the cement

slurry s directedo the argetntervaland he evel of pressuremposed n

theslurry.

TheBradenheadechniquesonsist f spotting ement lurryacrosshe

mrget nterval by use of a workstring o placea balanced lug. The

workstrings pulledout of the plug, he annulus losedn and squeeze

prcssures applied.Thissequencef operationss illustrated y Figure33,

takenrom Reference3.

Using heBradenheadechnique llowablesqueezeressures limitedby

casing tringandwellhead urststrength.Also, his methods suitedo

wellshavingonlyone nterval o be squeezed.

A Bullhead queezesarypeof Bradenheadqueeze hichdispensesith a

work string. The cement lurry s pumpeddirectly nto the casingat the

surfacewith thehope hat t will find andenterhe argetnterval. The ack

of control and chancesor contaminationnherent n this methodare

obvious.

Squeezeackerechniquesmployeithera drillablepackeraiso eferredo

as a retainer) r a retrievable acker shownasFigure34 from Reference

18). Two typesof drillablepackers re llustratedn Figure35 also rom

Reference8.

-offers connol over slurry placement nd

achievessolation f theentire asing tringandwellheadrom highsqueeze

pressures. he ocation f a squeezeackerelative o the argetnterval s

important. f placedoohigh n thewellbore,arelatively argeamountof

potentiallycontaminating ellbore fluid entershe target ntervalaheadof

)

8 7



Figure 3

Bradenheadqueezeechnique

SPOT APPLY

CEMENT SOUEZEPRESSURE

RF/ERSECIRCULATE

-Schematicof Bradenheadsqueeze echnique normally

used on low pressure formations. Cement is circulated into

oface oot"n Oii t t pipe (teft), hen wetlhead,-orBOP, is closecl

icenieri-"no squdeie iresCure is apptied. Reversecirculat ing

ihrougn perlorations (right) removgs excess cement' or plug

can be drilled out-

8 8



Figure34

Retrievable queeze acker

8 9



Figure35

DrillableSqueezeacker

SlldlngVblve Popett hlve

the cementslurry. If placed too close to the target interval, any tendency

toward casing collapse,prompted by high squeezepressure,can make

removalof a rerievable packerdifficult if not impossible. For most wells a

retrievablepackershouldbe set 30-60feet above heperforations.

A retrievable packer is best suited to an operation that involves the

squeezingof more thanone nterval in a well. Sincea retrievablepacker s

not drilled (or drillable) following a squeeze ob, it can reduce the rig

charges or an operation. On the other hand, sincea retrievable packer is

not easilydrilted it shouldnot beused f theeconomic mpact of drilling an

inadvertently stuckpacker could be great. Drillable packers ncorporatea

9 0



checkvalve assembly;his can be an advantagen preventing lowback

followinga squeezeob.

A circulationsqueezeementingob, utilizing a packer,s a particularly

effectivemethodof stoppinghe low of unwantedluid behindpipe. For a

circulationsqueezehepacker s locatedbenveenheproductionntervalperforationsand perforations stablished t the sourceof

'theunwanted

flow, asshownschematicallyy Figrue35.1, rom Reference 6'

Figurc 5.1

RecementingewecnPerfo'rations

Circulations establishedusuallywith water)by pumpingdownthework

string,through he bottompcrforations,up through he primarycement

sheath, ut the top perforations nd nto the work string/casing nnulus.

Thewater s then ollowedby thecEment lurry;after hecementslurryhasbeenpumped,hework'strings stung utof thepacker, ulled o abovehe

top of the cementplug in thecasing,cleanedby reverse irculation,and

squeezercssures applied. In somenstances ater'beinga penetrating

fluid, will enter the lower interval and not communicateo the upper

perforations. Cementslurry is not a penetrating luid, and in this

circumstance ill oftencirculatewhetherwater did or not. The HTA{P

filter loss ateof thecement lurryshouldbecontrolledo around100m1n

9 1



3 .

30-minutesAPI, sothe entirechannclwill be invadedby cementand to

preventsticking he work stringwith cement ilter cakeoppositehe top

perforations.Also, thecement lurryusedor a circulationsqueezehould

haveamplehickeningime(ob timeplus1-2hours)or thesameeason.

Hieh Pressure

4 .

: High pressure queeze

cementings based n two misconceptions. nemisconceptions that

cement nins enter he ormationmatrix, heother s thatwhen hecement

fracturesheformation t forms a horizontalpancakewhich seryes san

effectivebarrier o vertical low. Actually,cementgrainswill not entera

formationmatrix havinga permeabilityof lessthan 100Darcies. Onencounteringporous, ermeableonnation;cement lurry oses iltrate o

the formationand depositsa filter cakeon the formationface. If the

pressure ifferential s high enough, he formationwill fractureandthe

cementwill enter he racturc.The racnrewill behorizontalf andonly f

the racturingpressures gfeaterhan he overburden ressure,onditions

thatapplyatvery shallowdepths.The esultof mosthighpressurequeeze

cementobs s depicted yFigure36(fromReference6).

Aside from the fact thatputting cement nto vertical racture wings"

extending way rom the wellboredoesnot accomplish nyuseful esult,

disadvantagesf highpressurequeezeementingnclude: anexcessive

amountof cements requiredand here s thehazardof openingup flow

paths hatwill be difficult to access ndseal.The only siruationn which

squeeze ementingn excess f fracturepressures justified is when

working n drillingmud. There s thchope, n sucha situation,hat he

mud will be transmitted way from the wellboreand cementwiil then

perform ts intendedunction.

Low PressureSqucezeCementings performedat pressuresess than

formation racturepressure.

It is not

intended to placecement n the formation. When squeezingperforations

usingthe ow pressurcechnique herate of cement ilter cakedeposition,

9 2



Figure36

Htgh pressure techntque. vertrcal fracture gener'

ated by htgh pressuresqueeang.

which n turn s rclated o theHTAIPAPI fluid loss ateof thecements

very mportant.This s demonstratedn ageneralwayby Figure37 (fromReference6).

There are wo potentialproblemswith extremelyhigh cement iltration rates

for low pressuresqueezecementing of perforations. The most fluid

conductiveperforation(s)will be treated nitially, and if that perforation s

near hetop of the nterval,and f a high fluid loss rate cementslurry is used

thatperforation(s)will be the only one reated. The otherpotential problem

is related to sticking the work string by excessive ilter cake build up. A

technique hat is employed n the field to encourage overageof the entire

perforated nterval is referredto as"hesitation". The pressure s increased

to approach the predetermined maximum squeezepressure, it is then

allowed to bleed backa few hundredpsi, if it will, and the cycle is repeated

until the squeeze rcssureholds or 5-10minutesafterpumping s stopped.

In calculating hemaximumpermissiblesqueeze ressure or a low pressure

squeeze,hehydrostaticpressurcon thetarget nterval, aswell as he

9 3



Figure37

Schematuc f cement ftlrcr cakebw]d-up

appliedsurfacepressuremust beconsidered.The need or consideringboth

pressuress illustratedby the following calculation. Considera well with

perforations o be squeezed t 8000 feet. The fracture gradient s 0.75psi/foot; 6.50 lbs/foot 2 7/8" tubing will be usedas work string. The

cementslurry s 5 bbls of 15.8ppgclassG cement ontaininga FLA (Fluid

Loss Additive). The maximum bottom hole pressure BHP) to avoid

fracnring is:

8000feet x 0.75 Psilfoot = 6000Psi.

The hydrostaticexertedby the cementslurry when t is in the bottom of the

nrbing s:

5 bblx 172.76tlbbl = 864 eet

(for6.5 b/ft2 7/8" tbg)

864 eetx .052psigd x 15.8bs= 710psift lbs eal

9 4



If thewell is loadedwith 9.0ppg field brine hen hehydrostatic ressure

exerted v the brine s

8000'-864'=7136feet

7136.052F#x e.oS=

333esi

Thus he maximumallowedsurface umppressure ould be

6000psi- 710psi- 3339 si= 1951 si

Note: This calculationsconservatives hehydrostatic ressure4049psi)

is calculatedwith thecement lurrycompletelyn

theubing. When heplug

is balancedn the bottomof the casing, he contribution o hydrostatic

pressure y theheavier ement lurrywill be somewhatess.

3. WellboFEnvironmentConsiderations

In theplanningof a squeezeementingob it is important o considerhe

environmentntowhich hecementwill beplaced

The Fluids in thewellboreand hetarget ntenral, deally, will beclean,

solids-free,water-basedluid. The predominanteason hat perforation

squeezesre oftenunsuccessfuln first anempt s because omeof the

perforationsare pluggedwith mud. If mud has been(or is) over the

perforations,perforation washing tools are sometimesusedprior to

performinga squeezeob. As a minimum, in other than a clean

environment, waterwash/preflushhouldprecedehe squeezeementing

slurry.

Temperaturcs an mportant arameter.The significance f correct iltration

rate and hickening imeto theperformance f a squeezeementingslurry

has beendiscussed, nd temperatures the most important parameter

controlling hese roperties.

Stickinga work stringor aretrievableackerpanicularlyn a deepwell) s

much cgretted nd ongrememb€rcd

9 5



4 .

Pressurenformationneeded henperforminga squeezeementob is the

pressure ufficient o keep he well undercontrol,but below that which

would result n fracturing he formation. By controllingbothpumpand

hydrostatic rcssuresheBHP canbekept n thisrange.

FormationCharacteristicsre mportantn thedesignandexecutionof a

squeezeementob. Theadmonitionegardinghecontrolof cement lurry

fluid loss ateapplieso perforationsntoporous, ermeableormations. f

the formationhas ow matrix permeabilityandvugularporosity, hen a

differentapproachmay berequiredo avoid low-backof thecement lurry

after the squeezes attempted.What s oftendone s to usea two-stage

squeezeementing ystem,he first stages intended o enter hevugs

and/ornatural racturesbut not invade he formationto an appreciableextent; he second tages thenstopped y the irst stageand emainsnear

thewellboreo seal heperforations,hannel, tc. The irst stages usually

composedf ahigh luid loss atecement ontaining ridgingmaterialor it

may bea thixotropiccement;he second tages a moderateluid loss ate

slurry.

SpecialOBerarions

Specialsqueezeementing perationsnclude: top of primary cement

(TOC)augmentation,asing amageepair,iner oprepairandcasing hoe

repair.

In somewells TOC is belowthe desiredor requiredelevationeither by

design in someolder wells) or because f someproblemduring the

primary cementingoperation. Cementcan be broughtto the required

elevation yperforatinghecasing ear heexistingTOC andsqueezinghe

requiredamountof cementnto the annulus. f the "new"perforatiOnSre

well off-bottoma cementbasket, ridgeplugor sandbedwill berequiredo

prcvent all of thecement.An operation uchas his s in essence primary

cementob conductednderadverseonditionsno pipemovement nd

mudof unknownpropertiesn the annulus).A waterpreflushshouldbe

usedand f porous ermeableormationswill beencounteredhe luid loss

rateof the cement lurryshouldbeconuolled.

9 6



TheRepairof DamagedSplitor Holed)Casingby squeezeementings

similar o theaboveoperationwith oneexception.As there s noneedor

intent to fill theentireavailableannuluswith cementslurry, it is preferred

that hecement lurrybecomemnrobilesoonafter t passeshrough he split

or hole, and fluid loss ratecontrol will be counterproductive n most

instances. or bothof these perations cement lug shouldbe eft in the

casing o be drilledafterWOC;the obsshouldnot beoverflushed

Repairof aLiner Top is sometimesequiredpanicularly if the iner is in a

critical pan of the hole, .e.,oppositea gascap. Defects n the liner top

regionareoftenof very smalldimensionsnda low fluid loss atecement

shouldbe used. Liners are often set at greatdepth and very high

temp€rarures re encountered o slurry designfor this application s

important.

CasingShoeRepair If theshoeof a surface r intermediateasingstring

fails a PIT, thenrepair s required- Repair s accomplished y squeeze

cementing.Thereare wo considerations ith regard o slurrydesign or

this operation.Fint, thecement houkidevelophigh compressivetrength.

Second, incehe ailureat the shoe anbedue o formation racturing,he

cementslurry used or this purposeshouldnot extendthe fracture.

Therefore, he desiredcementslurry for this applicationwill be an

inefficientracturinglui4 i.e.,havemoderateo high luid loss ate.

5. On-SiteConsiderations

The amountof cementslurry required or most squeeze ementing

operationss rclativelysmall.Many obsareperformedwith 10bblsor less

of cement lurry. Becausc f this,batchmixingof thecement lurry s the

preferredmethod.Someecirculatingmixen havesufficient olume o suit

them or the barchmixingof squeezelurries.

Thework stringuscd or squeezeerrentingshouldbepressureestedo the

intended queezercssurc.A leak n thework stringdownhole an esuitn

stickingof thepiPe.

9 7



6 . SoueezeobTesting

AfterWOCthe squeezeob should epressureestedn thc directionand o

the level it will encountern service. For example f a casingshoe s

repaired y squeezeementingt shouldbe ested singappliedpressureo

thesameevelaswas used or thePIT. If perforationsn aproducingwellare sealed y squeezeementingheyshouldbe testedby swabbingluid

from the well so formation pressurewill be imposedacrossthe

perforations.Anainment f squeezeressurc uring he courseof the ob

doesnot constitute testof the ob.

9 8



List of References

t. Smith,D.K., Cementing,Monograph olume4, HenryL. DohertySeries,SPEof AIME

(publishers), allas 197 ).

2. API Specificationor MaterialsandTestingor Well Cements. PI Specification 0,3rd

Edition, uly 1, 1986.

3,Dougle,D.D.andHel lawel lA., ' 'TheSol id i f icat ionofCement ' ' ,@July

1977,pp.82-90.

4. Lea,F.M., The Chemistr.v f Cementand Concrete, dwardArnold (Publishers) td,

London 1976).

5. Hunt, L.P., "Predictionof Thickening Time of Well Cements rom Blaine Air

Pernre abil i t y' ' , ,Vol. l6,pp. 190-198' Pergamo nPress

Ltd.,New York (1986).

6. Brooks,F.A., "High Temperanrre/Iligh ressure iltrationRateof SqueezeCemenring

Slurries",Proceedings f SPESqueeze ementingSymposium,CorpusChristi,Texas,

March2, T976.

7. Rao,P., Sutton,D., Childs,J., andCunningham,'W.,An UtrasonicDeviceFor Non-

Destnrctive estingof Oil-Well Cements t Elevated emperanrresndPressures",aper

SPE9283presentedt SPE-AIMEFallMeeting,Dallas,SeptemberI-24,1980.

8. Goddrey,W.K., "Effectof JetPerforatingn BondStrength f Cement", gsacljs

AIME (1963), oL.243.

9. Dowdle,W.C., and Cobb,W.M.,

"Estimation

of StaticFormationTemperaturesromWellLogs",paperSPE4096prcsentedt SPE-AIMEFallMeeting,October1974.

10. Wedelich,H., Goodman,M.A., andGalate, .W., Key Factors hatAffect Cementing

Temperatures",apetr PE-IADC16133 resentedt SPE/IADCDrilting Conference,ew

Orleans, arch15-18, 987.

\_ 11. HalliburtonEnelish./Metricementing ables.HalliburtonServicesPublisher), uncan,

Oklatroma1981).

9 9



lZ. Suman, .O.,andEllis,R.C., CementingOil andGasWells-Part", WorldOil, (1977).

13. API Soecificationor CasineCentralizers,PI Spec10D,3rdEdition,February 7,1986.

14. Kunze,K.R., Obtaining nd VerifyingQualityCementBlends",PaperSPE 15576

presentedt SPEFall Meeting,NewOrleans,October -8' 1986.

15. Parker,P., andClement,C., "BasicCementingPart8" Qll-4s!-Ges.JgulgAl,(]977).

16.DowellSchlumberger,@,NovaCommunicationsLtd.'(Publishers),

London 1984).

lj . McElfresh, .M.,andCobb, .A.,"ChemicalThickening ime Test or Cement lends",paperSPE10220 resentedt SPEFallMeeting, anAntonio, exas,October -7,1981.

18. Smith,D.K., Cementing,MonographVolume4, Henry L. Doherty Series,Revised

Edition,SPEof AIME (Publishen), ichardson,exas,1987).

19. Haut, R.C., and Crook, R.J., "Primary Cementing Optimizing for Maximum

Displacement",J.!4QIL November,1980).

20. Mclean, R.H.,Manry,C.W.,andWhitaker,W.W., "DisplacementMechanicsn Primary

Cementing", 1967,P.215.

2I. Haut,R.C.,and Crook,R.J.,"LaboratoryInvestigationf Lightweight,Low-Low-

ViscosityCementing pacer luids", aperSPE10305 resentedt SPEFall Meeting, an

Antonio,October -7,1981.

22. Kline,W.E.,Kocian,E.M., and Smith,W.8., "Evaluationof Cementing ractices y

QuantitativeRadiotracerMeasurements",aper ADC/SPE14778presented t 1986

IADS/SPEDrilling Conference,allas,February 0-12'1986.

23. Suman,G.O.,and Ellis, R.C., "CementingOii andGasWells - Part 6", @!L

(1977).

1 0 0



24. Kolthoff,K.W., andScales, .H.,"ImprovedLinerCementingechniquesor Alaska's

PrudhoeBay Field",paperSPE10756 resentedt 1982CaliforniaRegionalMeetingof

SPE,SanFrancisco,March 24'26,L982.

25. Lindsay,H.8., Jr.,"New

ToolsMakeLinerRotationDuring Cementing ractical",WorldOi l (October 981)65-174.

26. Fitzgerald,D.D., McGhee,B.F., andMcGquire,J.A., "Guidelinesfor 90VoAccuracyn

Zone IsolarionDecisions",paperSPE 12141presented t SPEFall Meeting, San

Francisco, ctober -8,1983.

27 Cooke,C.E., RadialDifferentialTemperatueRDT)Logging A NewTool for Detecting

andTreating low BehindCasing",ournal f Petroleumechnology,une, 979.

28. Parcevaux, A., andSault,P.H.,"CementShrinkage ndElasticity,A NewApproach or

a GoodZonal solation,"paperSPE13176presented t 1984Fall Meeting,Houston,

September619,1984.

29. Cooke,C.E.,Kluck, M.P.,andMedrano,R. "FieldMeasurementsf Annular hessure

andTemperanre uringPrimaryCementing",aperSPE11206 rcsented t 1982Fall

Meeting,New Orleans, eptember6'29,1982"

30. Webster,W.W.,andEikerts, .V.,"FlowAfter Cementing Field andLaboratoryStudy",

paperSPE8259prcsented tL979FallMeeting, asVegas,September3-26,1979.

31."Plug Back Cementing",Drilline Technolog]'Series'Number ll23' producedand

distributed yPetroleum xtension ewice, heUniversity f Texas t Austin.

32. BJ Hughes, giEA!-B.eek,Copyrightby BJHughes,USA (1982).

33. Suman,G.O.,andEllisR.C., CementingQil andGasWells Part7" WgddtQil,pp.57-

65,(1977).

34. Smith,R.C.,Beinrte,R.M.,andHolman,G.B.,"ImprovedMethodof SettingSuccessful

Cement lug",Journal f Petroleumechnology.November,984), p. 1897-190a.

\-- 35. Beimte, R.M.,"Flow Behaviorof an UnsetCementPlug in Place", 53rd Annual SPE of

AIME Fall TechnicalConference,October,1978),preprintNo. SPE-7589, 978.

1 0 1



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