SPESPE 13176

Cement Shrinkage andZonal Isolation

Elasticity: A New Approach for a Good

by P.A. Parcevaux and P.H. Sault,* Etudes& Fabrication Dowell Schlumberger

●SPE Member

Copyright 19S4 Society of Petroleum Engineers of AlME

This psper was presented at the 59th AnnualTechnical Conferenceand Exhibitionheld in Houston,Texaa, September 16-19, 19S4. The material is eubiect to correctionbv the author. Permissionto COPYis reatfictadto an abstractof notmore than ~ words. Write SpE, 6~ NOnhcentral Expressway,Drawer 64706, Da~las,Texas 75206 USA. Telex 7S0969 SPEDAL.

ABSTRACT

Characterization of cement bonding performancerequired the set up of new pieces of laboratory equip-ment. The evaluation of cement bonding property hasbeen performed under controlled temperature andpressure curing conditions, and was proved to be re-producible with a very small dispersion of results.Shear bond ha,sbeen tested through mechanical andhydraulic means, and related to other parameters suchas volumetric shrinkage development, stress-strainrelationships, permeability, and compressive strength.A laboratory and field experimental program has beenconducted to compare the bonding capability ofstandard cement compositions with that of cementmodified with a bonding agent. Laboratory and fieldresults are in perfect accordance.

INTRODUCTION

A primary cement job must fulfill multipleconditions in order to keep drilling and productionscosts at a minimum level throughout the life of thewell. The most critical objective is to provide agood isolation between the producing zones up to thesurface, and this over a time period of several years.No completion or formation fluid movement, either gasor liquid, should be possible at any time through thecemented annulus. Gas migration during cement slurrysetting has been previously investigated (1) (2), andsolutions suggested. This paper focuses more on thecapability of hard cement to prevent communicationand to provide a long lasting tight seal.

In the field, the cement bond effectiveness ismost often evaluated through acoustic measurements.Logging techniques describe the cement-to-pipe andcement-to-formekion couplings thrcJiightiheV~lOCitjjand the attenuation of a sonic signal. If no logs arerun or if the formation characteristics make theirinterpretation delicate, the communication betweenzones is sometimes tested by injecting water orcompletion fluid and measuring either directly the

References and illustrations at end of paper.

fluid flow or the pressure transmission htween twosets of perforations. However these tests can damagethe formation by fracturing or plugging, or can evenruin the cement-to-pipe and cement-to-formationcouplings.

Poor mud removal is generally identified as themajor source of communication problems, although ithas been noticed that poor bonding at the interfacecan occur even if the mud has been properly removedfrom the annulus (3). Other recognized sources ofproblems are cement slurry properties like fluidloss and free water (4) (5). But bonding Perfo~ancesare also widely affected by cement chemical shrinkageduring hydration, by stress changes induced by down-hole deformations or variations in hydrostaticpressure, and by the nettability and the surfacecondition of the casing and formation (7) (8).

It has been generally recognized and acceptedthat the bond across the permeable producing intervalitself is not the key parameter : whatever thequality of the bond across the permeable zone, thefluids can still migrate upwards within the formationand channel at the interface with the overlyingformation. It is therefore much more important toprovide a tight seai across the imperioeableZUII.=

-----

that form the barriers.

Though the problem can be identified in thefield, there is today a lack of reliable equipmentfor testing cement bonding properties in the labo-ratory. When such tests are run, cement bondingproperties are generally evaluated through shearbond and compressive strength measurements.Hydraulic bond tests are very seldom performed. Thereis also very scarce data regarding the contribution.= L1----k----- --* ..k.....”.1UL UI= UU1=L ~.4E=,&b~.h==.ti=.prepartxesr such.asshrinkage and stress-strain relationships, to itsability to properly isolate zones.

This paper describes first a set of laboratoryequipment for measuring cement physical propertiesrelated to zonal isolation under controlled pressureand temperature. These properties are namely shear

2 CENENT SHRINKAGE AND ELASTICITY : A NEW APPROACH FOR GQOD ZONAL ISOLATION SPE 13176

and hydraulic bonds, shrinkage and permeability. The- .= -:-- -c .-.-ka+=conLri.D”uLLullUL C-L,,“J.~h~~= p~qerties tQ bonding

effectiveness is investigated and compared also toother cement mechanical properties like compressivestrength and deformability.

Results obtained with this equipment are thenpresented and discussed. Several standard cementslurry compositions are evaluated and compared to aslurry modified with a Bonding Additive (referred tohereafter as BA cement). Results of field testssupport the conclusions of”this laboratory evaluation

CHARACTERIZATION OF CEMENT BONDING PROPERTIES

Criteria for designing laboratory equipment

. L.__= ----- . . A.A ..” ~v*-evtiae 3~eAs m=iiciufieu, ~cura,.L -l.=l..= ~.w=-.---.

most important in front of an impermeable medium.Therefore for standardizing the bond strength measurements, a cylindrical piece of carbon steel pipe withcontrolled roughness is taken as the impermeablemedium.

Previous data on cement bonding propertiesgenerally show a wide dispersion in the results.Comparison is also very difficult between the diffe-rent sources of published data. All these discrepan-cies result from experimental artefacts like thermaland hydraulic deformations of cells and sampleswhich are most often cured in an autoclave under highpressure and high temperature conditions, and thentested at room temperature and atmospheric pressure(7) (8). As a consequence iieiieqiiipiiiieiitEGst 5*designed so that both curing and testing of thecement samples are performed in the same set up andunder the same conditions without having to manipulatthe samples. Another reason for these variations indata may result from the very different designs of thtesting cells used (various geometries, sizes,roughness).

The effects of model size and geometry on bondstrength measurement have been thoroughly studied

--a -1.-G..lI.-.,.,<-”rn,iilel inn= have ~~en Used(10; , a,,u u.= J.”4.A””A.,.J .j..--e--..-- ..-.

for designing the cells :

The failure in a cemented pipe-pipe annulusalways occurs at the cement-inner pipeinterface. The force-to-stress relationshipbeing nearly the same for the outer and innerlongitudinal surface area of a pipe, it has‘--- ‘--ad-a tO St!!dy‘J.eil?t~~E3C~ Qf MlLJetxl U.=L4.IA.=U

internally cemented cylindrical pipe. Thiseliminates additional problems of radial and=xial Centralization.

The shear bond strength is unaffected by pipediameter but is dependent upon the length-to-diameter ratio because of the stress distri-bution along the interface. It has also beenshown that the influence of length is negli-gible provided the length-to-diameter ratiostays below 1.5. TO remain within thesespecifications, in both shear and hydraulicbond cells the sampie noitieris a 5 em ~iui~~

diameter 5 cm long cylindrical pipe.

Shear bond strength apparatiis

The body cell is a stainless steel chambercapable of withstanding 20 Mpa pressure and 100 deg.Ctemperature (Fig. 1). The previously described cylin-drical steel mold is inserted into the cell betweentwo shoulders on top of a piston. For testing, thecell is heated up at test temperature and the cementslurry, also at test temperature is po-ure6 iiItX2 tk.emold. Hydration pressure is applied through a nitrogenpressure regulator. The cell assembly is put in an airconvection thermostated oven. The piston is perfectlycentered with two “O,,rtigs, ad is able to move ‘p

axially with very little friction (less than 0.1 Mpa)when hydraulic pressure is applied from below. Aftera given curing time, a fluid is pumped at a constantflow rate onto the piston, converting the stress on~he cement from an hydraulic to a mechanical one.

Pressure linearly increases up to the point where thecement-to-pipe link breaks. At this stage the pressuredrops to a residual value corresponding to the dragforce of the cement slipping along the pipe. Thisresidual pressure depends very much on the pump rateand should therefore not be considered. ‘Thepeakpressure, which has been shown to be independent onthis pump rate, multiplied by the ratio of samplecross sectional area to longitudinal surface area istaken as the shear bond strength.

Hydraulic bond and permeability apparatus

Hydraulic bond and permeability are measured incells similar to that of shear bond but withstandinghigher pressure [50 !@a) for possible application ofa confining pressure. Test fluid is also directly

applied onto the cement sample (Fig. 2).

When testing the hydraulic bond of a cement, the;lurry is placed in the already described carbon steelmold, the cell is saturated in place with water, andthe cement is hydrated for a given period of timeunder temperature and pressure. When ready to test,the hydration pressure is maintained on the cementsample, but water hydraulic pressure is graduallyincreased. The outflow rate is then recorded. TOinsure that the flow is not due to pipe deformation,the steel mold is perfectly centered in the cell anda given annular space left. This s~ce is saturatedwith water and its pressure is controlled. Thisannular clearance can also be used for monitoring thepipe deformation as another parameter of investigation

For testing the permeability of a cement, thesteel mold is replaced by a deformable rubber membram(Fig. 3). A confining pressure is applied on theexternal side of the membrane to prevent any flow atthe interface.

Cement slurry compositions and testing procedures

Results reported in this paper have been obtaine<on cement slurries made from Class G cement and freshwater to which organic dispersant and retarder havebeen added when required. Some of these slurries havealso been modified with the Bonding Agent at concen-.--.2----‘“..”<. k+”..p Q ~q~ ~o% by Volm of&LaLAui4aAc4,s~An3---”-- .slurry. They were mixed at a standard slurry density

SEW 13176 Philippe PARCEVAUX - Patrick SAULIT 3

1.9 g/cm3 when using only Portland cement. The slurryspecific gravity has been decreased down to 1.58 whenusing blends with a pozzolanic material or increasedup to 2.05 with barite. Each slurry is mixed in aconstant speed Waring Blendor according to API speci-fication 10, and heated up in a consistometer at thedesired test temperature following the proper sche-dule. It is then transferred to the preheated cell andcured at the proper test pressure and temperature.

Cement shear bond strength development

Each cement slurry composition was tested simul-taneously in quadruplicate. The reproducibility isexcellent with less than 15% dispersion on more than90% of the runs (Table 1). At 20 deg.C, a conventionalcement system reaches its maximum shear bond strengthwithin 7 days, where it levels out and stays almostconstant up to 28 days (Fig. 4). Increasing thetemperature speeds up the shear bond strength develop-ment, but the maximum strength is reduced by about 50%(i.e. from 8.0 to 3.6 Mpa) when the temperatureincreases from 20 to 70 deg.C. There is then a time-temperature effect on shear bond strength developmentwhich must be considered when characterizing theshear bond property of a cement. At close to ambienttemperatures cement curing must be carried on for atleast 7 days before consistent results can be obtainedAt 70 deg.C 3 days are a minimum. Furthermore, theshear bond strength depends strongly on the cementslurry density : it increases with density (Table 1),when baryte is used as the weighting agent.

The addition of the Bonding Agent proves to bevery beneficial on the long term, as BA cement keepsdeveloping shear bond strength even after 28 days#hen a conventional one levels off after 7 days.After 28 days at 20 deg.C, BA improves the shear bondstrength by 45%, and by 89% after 3 days at 70 deg.C.3A improves the shear bond strength whatever theslurry density, but the lighter the slurry, thehigher its relative efficiency.

Hydraulic bond and permeability measurements

The curve of flow versus differential pressureis a two-slope curve (Fig. 5). The first part ischaracteristic of the permeability of the cementmatrix itself. This has been correlated with perme-ability measurements (0.005 mdarcy for a neat cement).l’hesecond part shows a dramatic increase in flowrate after the interface has been damaged (0.3 mdarcyof equivalent permeability) . The pressure required toinitiate the failure is very close to the pressurecorresponding to the shear bond strength as measuredpreviously. This correlates with the visual obser-vations of the cement moving in the cell. As bothshear and hydraulic bonds give the same results, itis much easier and simpler to run only the shear bondtest, when only the stress at the time of failure isrequested. But the hydraulic bond test gives tb.eadditional information of the increase in permeabi-

lity at the interface due to damage.

When BA cement is used, the pressure required totimage the interface is also equivalent to the shearbond strength, then much higher than for a conventio-nal cement. But what is still more important is thatthe damage induced by this failure is then very small:the equivalent permeability after failure is 0.084mdarcy or 3.5 times less than for a standard cement.

CEMENT SHRINKAGE DEVELOPMENT

Cement chemical shrinkage

Cement shrinkage is a very important factor,contributing both to gas migration (early porepressure decrease), and to interracial bonds. Thereduction of the absolute volume, which occurs whenwater and cement particles combine to form hydrates,is the phenomenon that causes this chemical shrinkage.This wlume change proceeds continuously, though atdifferent rates, from the time of cement mixing tillthe time of final hardening several weeks or monthslater.

Just after mixing, shrinkage occurs at a lowrate because of minerals dissolution. Then theshrinkage is very high during cement settin9 (hYdra-tion of C3S) and it slows down during the hardeningphase, as the hydration of C2S and C3A phasesproduce a long term low rate shrinkage (11). As aconsequence, cement shrinkage must be monitored notonly as a function of time but also as a function ofcement hydration. For that, a simple method is des-cribed in (12). It consists in recording cement tempe-rature versus time. When cement temperature starts to

exceed the test temperature, it corresponds to cementthickening or initial set time. When the temperaturereaches a maximum, cement is at its final set(appearance of a cohesive structure). EarlY h=deningcorresponds to the next period of time, during whichcement temperature decreases again down to testtemperature.

Cement shrinkage is split between a bulk (orouter) shrinkage, and a matrix (or inner) one. ‘l’herelative importance of these two types of shrinkagedepends on the balance between the intergranularstresses and the local tensile ones which are inducedby the shrinkage. Inner shrinkage creates, at thetime of cement setting, a secondary or extra porosity,mainly made of free and interconnected pores, whichenhances cement permeability (12), and thereforefavors the phenomenon of gas migration.

This chemical shrinkage has been widely studiedin the construction industry, e.g. at ambient curingconditions. It has been demonstrated that eachhydraulic phase develops its own shrinkage. C2S isthe hydraulic phase that shrinks the least and C3Athe one that shrinks the most (13). Total shrinkageat ambient conditions is reported between 4 and 6%by volume (11) (13). Of this total shrinkage the bulkpart accounts for 1 to 1.5% (14), but depends strongllon mixing conditions, water to cement ratio, andtime since mixing taken as “initial” (11) (14).

There are two common techniques used to quantifythe shrinkage : it is either continuously recordedthrough dilatometric methods (13) (14), or measuredat various stages of hydration using Porosimetry (12)

Shrinkage cell

The shrinkage apparatus (Fig. 6) is made of a500 cm3 stainless steel pressurizable chamber immer-sed in a thermostated water bath. It contains thecement sample (20 to 50 cm3) , which is cast in aperspex tube (2.54 cm in diameter and 7 to 10 cm inlength). The cement sample is in direct contact withthe rest of the cell which is saturated with water.

4 CEMENT SHRINKAGE AND ELASTICITY : A NEW APPROACH FOR GOOD ZONAL ISOLATION SPE 13176

A pressure regulator applies a constant nitrogenpressure to the top of a piston which in turnmaintains the curing pressure constant throughoutthe test. The displacement of the piston is monitoredby an LDT transducer and continuously recorded.Cement shrinkage is then calculated from any volumechange in the cell, either expansion or contraction.The slurry temperature is recorded in an extra cellsubmitted to the same conditions.

Special attention has been paid to pressure andtemperature secondary effects : the cell is preheatedand saturated with water at the test temperature toavoid thermal expansion of the chamberor the water.Initial compressibility of water and cement sampleare thus eliminated. only the total volumetric shrin-kage is recorded. The bulk shrinkage could also bemeasured by a similar technique if the cement sampleis sealed in a rubber membrane before casting it inthe perspex tube. But there occurs always the develop-ment of a layer of bleeding water at the top of thecement sample. As this volume of “free water” is notproportional to the volume of sample, the resultsobtained this way are erroneous, unless a specificassembly is mounted on the cell to collect it at theright time (11).

Parameters investigated

Shrinkage has been recorded versus time oncement slurries at a density of 1.9 g/cm3 containingvarious concentrations of Bonding Agent, as a functiolof temperature (20 or 70 deg.C) and pressure (0.5,4.0, 10.0 Mpa). Cement rheology was adjusted withorganic dispersant. Lignosulfonate retarder has alsobeen added so that the thickening time of all

–..–—L.——.––LL-siurries was similar wna=ever ~ne test temperatiire.

Shrinkage development

Typically cement shrinkage exhibits an S shapecurve (Fig. 7). The first part of the curve with alow slope, proceeds up to cement maximum hydrationtemperature, e.g. up to cement setting, and iscertainly the portion of shrinkage related to cementpore pressure decrease. The second part, or highslope, proceeds during ‘earlyhardening of cement(from 5 to 10 hours), and after 24 hours a stabili-zation period occurs. Tests run for 48 hours at20 deg.C generally exhibit a second high slope periodafter the stabilization which might indicate a delaybetween high rate C3S hydration and the beginning ofC2S hydration. On the tests run at the highestpressure (10 Mpa) this second high slope completelydisappears and this could be attributed either to adelay in C2S hydration or to a different hydrationprocess generating almost no secondary shrinkage.When we consider the shrinkage at 24 hours (Table 2),we can say that the higher the temperature, the highethe shrinkage (15% increase from 20 to 70 deg.C). Onthe contrary, shrinkage seems to decrease whenpressure increases, especially after 48 hours.

At any stage of hydration, BA cement exhibitsdelayed and reduced values of shrinkage. Increasingthe amounts of the Bonding Agent significantlydecreases the initial shrinkage, up to half the valueof that of a neat cement. At 24 hours, the shrinkageis reduced by 20 to 40% by the Bonding Agent (depen-ding on the amount used).

mechanical CHARACTERISTICS OF CENENT

Excessive downhole deformation of the casinglardware can lead to damage of the cement sheath. It?as therefore attempted to correlate cement bonding?erfonnance, measured as previously described, to itsmechanical properties, mainly the elastic stress-;train relationship and the compressive strength.

Elastic properties

The mechanical properties below the failurepoint of various cement slurries have been measured%nd compared to that of a 8A cement. Cement slurries~ave been mixed according to API Spec 10 at a density>f 1.9 g/cm3 with respectively O, 9.4 and 18.8 percent>f Bonding Agent by volume of slurry. After curingthe samples for 28 days in a thermostated water bathSt 25 deg.C and atmospheric pressure, the sampleslave been tested in a triaxial cell. Each cementsample was submitted to an axial stress, with a:onstant 10 Mpa confining pressure. Axial and radialstrains were measured as a function of the appliedstress.

In the range of stress investigated, the cementDehaves as an elastic material, whether BA is added ormot. But, the higher the amount of Bonding Agent, themore elastic the cement sample (Fig. 8a and 8b). Underthe same loading conditions, the axial strain is twicess large for a cement containing 18.8 percent of BAas for a neat cement. The radial strain is alsoincreased by 40% in these conditions. This makes BAcement more capable of supporting without damagereversible stresses induced, for example, by thedrilling progress or the replacement of a drillingFiuiciby a coiiIpletiCIiifl-uid.“- ‘-----L-.‘“.----&---111*S&M.upsLLy yuaL.aAALA=s

a better sealing capability.

Relationship between shear bond

and compressive strength

Shear bond and compressive strength have beenmeasured on different cement slurries cured under thesame conditions. There seems to be no particularrelationship between shear bond and compressivestrength (Fig. 9). In most cases, the shear bondstrength accounts for 10 to 20% of the compressivestrength, although for high compressive strengths(above 38 Mpa) shear bond strength stabilizes at aconstant level whatever the compressive strength.

DISCUSSION

‘Thenew pieces of equipment which have been deve-loped allow the characterization of cement bondingproperties, along with the comparison of differentcement slurry compositions.

Cement bonding capability has been characterizedby a stress, determined through shear bond t&sting,and an equivalent interracial permeability afterdamaging the bond, determined through hydraulic bondtesting. Cement shrinkage and elasticity directlyinfluence its bonding properties, the lowest shrinkageand highest elasticity providing the best sealingeffect. As no interracial permeability could bemeasured before damage, it seems that shrinkage doesnot lead to the development of a microannulus but to

SPE 13176 Philippe PARCEVAUX - Patrick SAULT 5

the creation of discrete pores the interconnexion ofwhich decreases as hardening proceeds. Then theamount of shrinkage could certainly be correlated tothe percentage of unbounded surface. As a consequence,cement shrinkage is more related to shear bond

.L -1---4-:+..4. ---- ‘.--1i-a,+~Q @&=,J-Streiigul,“W-bileeLa=LAb.Gy .= -.= ..-....k-lic damage. On the contrary, compressive strengthdoes not influence bonding parameters, except maybe atvery early ages. This result is not really surprising,as compressive strength is a physical property of thecement matrix, while shear and hydraulic bonds arephysical properties of cement to pipe or formationinterface.

As is also the case of other standard tests,like the API fluid loss or free water tests, these

experiments do not allow a direct scale-up of labo-ratory results to field conditions. Although downholepressure and temperature are simulated and pipe defor-mation is monitored in the hydraulic bond cell, thesetests are mainly indicative and comparative. Thesepieces of equipments have not been designed toactually simulate well conditions, but to test andcompare properties of cements. Therefore the geometryof the ~e~~ fioe=no+ .++amntc ~0 EeprQdIJL2estress. ..-.-r--distribution at the interface and failure propagationsimilar to those occuring in a wellbore. The defor-mation history of casing ~ cement and formation isalso not simulated.

A real scale-up laboratory study would certainlybe time consuming and technically risky. Neverthelessthe type of experiments discussed here are highlyvaluable for quantitatively comparing different cementsystems, and for explaining some communicationproblems occurring in the field.

..I_.L..._l._..-Nsny primary cement pus IIdVe JXHL perfa.—mec?todate with slurries of different quality in order to

appreciate tie effect of the BA cement. In all tiecases where the cementing parameters have been wellcontrolled and when the results could be analyzedthrough acoustic logs or communication tests, 8Acements have demonstrated their ability to improvethe bonding and then to better isolate zones, every-thing else being equal. The following examplesillustrate the excellent agreement between the resultsfrom both the laboratory and the field and as aconsequence assess the validity of the laboratoryexperiments.

CASE HISTORIES

More than 150 primary cement jobs have beenperformed worldwide using the BA cement. In mostcases, two different slurries, a lead conventionalcement slurry and a tail-in BA cement slurry havebeen mixed. This enables a direct comparison betweenthe bonding performances of the two types of slurries.The following examples, taken from Latin America,Middle East and Africa, are representative cases.

Case 1——

A 7 in. casing was set at 4253 m in an 8 1/2 in.open hole (average hole diameter was 9 in.). Welldeviation was 9 deg.C and BHCT 92 deg.C. Previouscasing was a 9 5/8 in. set at 3655 m. One centralizerper joint was run in the open hole section. The wellhad been drilled with a bentonitic mud at 1.35 s.g.,

%nd circulated for 2 hours while3reciprocating the:asing prior to cementing. 1.5 m of water was pumped

3 of a turbulent flowus a preflush, followed by a 3 m;pacer at 1.43 s.g., and by 16 m3 of BA cement. Dis-placement was done at 1600 l/innwhich is above the;a~cu~=ted ~riti~a~ pump rate for turbulent flow for

my of the pumped fluids. The bond log, run after$ days, showed excellent cement to casing and cementto formation couplings all along the cementedLnterval (Fig. 10). Furthermore, the top of cement,:alculated from caliper and fluid volumes at 3250 m,Ls in perfect accordance with TOC observed on the log.

Case 2

A 9 5/8 in. casing was set at 2854 m in a 12 1/4in. open hole. Previous casing was a 13 3/8 in. set at1211 m. Hole deviation was 27 deg.C, and casing wascentralized with 1 centralizer per 3 joints in open~ole, plus 1 per joint 30 m above and below the zones>f interest. The well was drilled with a bentoniticnud at 1.15 s.g. BHCT was 65 deg.C. 3 m3 of a water?lUS surfactant preflush and 5 m3 of a turbulent flowspacer at 1.32 s.g. were pumped ahead of a cementsvstem composed of 18 m3 of a lead dispersed andd-—..retarded Class G cement slurry mixed at 1.9 s.g. and>f 23 m3 of BA cement mixed also at 1.9 s.g. Displa-cement was achieved in turbulent flow at 2400 l/inn.I’hebond log, run 3 days later, is excellent throughoutl-k-u. “=”.-”+=-,-+;,-,”I-II= DA L-’=IU==.1G .==- G..”.. (Fig. ~~): ~-~ ~iff~~@lCe in

scoustic coupling between cement and casing orEormation for the two types of cements is very signi-Ej.cant and characteristic. This behavior perfectlycorrelates with laboratory data obtained on conven-tional and BA cements.

Case 3

A 7 in. liner was set at 3189 m in a 8 1/2straight hole. Liner top was at ~~48 m. Previous casin<was a 9 5/8 in. set at 2783 m. BHCT was 76 deg.C.Nhile drilling a high pressure zone was encountered at2902 m which requireda mud weight of 1.95 s.g. 2.5 m3~f water-surfactant preflush and 7 m3 of turbulentflow spacer at 1.97 s.g. were pumped ahead of thecement. The cement system was composed of 8 m3 of BAcement as a lead slurry to isolate the producing zones,and of 5 m3 of a tail in slurry containing dispersant,retarder, and fluid loss agent, both mixed at 2.0 s.g.The calculated limit between the two slurries was at3038 m. Displacement was achieved in turbulent flowat 1300 l/inn.AIIacoustic log was run 36 hours afterthe cementation (Fig. 12). Two logs were run, one atzero pressure and one at 14 Mpa. Both are virtuallyidentical, and showed excellent isolation throughoutthe BA cement. Again, a strong difference is noticedbetween the good bonding properties provided by the8A cement, and the average to poor one provided bythe conventional one.

Case 4

A 7 in. liner was set at 3733 m in a straight8 1/2 hole. Top of liner was at 2706 m, and previous9 5/8 in. casing shoe was at 2842 m. BHCT was at107 deg.C. Mud was a KOH lignosulfonate type at 1.4s.g., and was conditioned for 2 hours while recipro-cating the liner prior to the cementation. 8 m3 of

6 CEMENT SHRINKAGE AND ELASTICITY : A NEW APPROACH FOR GCJOD ZONAL ISOLATION SPE 13176

turbulent flow spacer at 1.5 s.g. was pumped ahead of8 m3 of a lead slurry (containing dispersant,retarder, and fluid loss additive) , and of 12.7 m3 ofa tail-in BA cement, both mixed at 1.9 s.g. Fluidswere displaced in turbulent flow at 1300 l/inn.Thecement log was run 3 days after and showed excellentbonding all along the BA cement interval, while thelead slurry exhibited only average bonding results.Furthermore no communication was evidenced during thetesting and acidizing of 5 different producingi~,tei.v.a~~Vs.=x,~lese fr~~ ezCi?Ctkr.

Case 5

A 7 in. casing was set at 1615 m in a 8/12 in.open hole with an average deviation of 8.5 deg.CPrevious 9 5/8 in. casing shoe was at 367 m. BHCTwas 49 deg.C. Mud was a lignosulfonate type at 1.3

s.9. A sta9e collar was set at 792 m, and a two-stagecement job was performed, due to a low fracturegradient. A total of 30 centralizers were run, withone every 2 joints in front of the zones of interest.13 scratchers were also used. Mud was conditioned for3 hours, and casing reciprocated during circulation.3.2 m3 of water preflush was pumped and followedby 13.5 m3 of BA slurry mixed at 1.9 s.g. Displace-—--& .... A--- *...-L..1 -..+. +71-..,ulellL Wa- UUZIC h LuJ.&JLALeL.L J.J.”W at 22!?.!2l,hm. Thebond log was run after 3 days and shows excellentcement to pipe and cement to formation bonds allalong the cemented interval (Fig. 13). The well wasperforated and communication tests proved the fullzonal isolation. Again a strong difference wasobserved on the logs between BA cement in the firststage, and conventional cement in the second stage.

CONCLUSIONS

.

.

.

.

.

Specific pieces of equipment have been designedand constructed for measuring cement bondingproperties. Reproducible data are obtained inthese cells when following the proper testingprocedure.

Cement bonding properties are now routinelyand accurately measured in the laboratory withthese cells.

Cement bonding propertiesa shear bond strength andmeability after damage.

Cement bonding propertieslated to cement shrinkaqe

can be expressed byan interracial per-

are directly corre-and elasticity. The

compressive strength has no influence on thebonding properties of a cement.

The field application of cement slurries withhigh bonding characteristics designed in thelaboratory with this equipment has resultedin significant improvement in the quality ofprimary cement jobs.

in s.it-uatiaiis‘wheregood prinia.-y-ce~e?,tatie?.sare absolutely required but difficult toachieve, a cement with low shrinkage and highelasticity, together with good mud removaltechniques, has proved to be extremely success-ful in providing the specified isolationproperties.

UNIT CONVERSION FACTORS

in = 3.937 008 E-01 * cmft = 3.280 840 E+OO * mga1 . 2.641 ’720 E+02 * m3bbl . 6.289 811 E-01 * m3psi = 1.450 377 E+02 * I@lbs = 2.204 623 E-03 * glbs/gal . 8.345 404 E+OO * g/cm3sack of cement = 94 lbsdeg.F = (1.8 * deg.c + 32.}(*)

.*)exact conversion factor

REFERENCES

1 Pamevzux, P. ,,. PicK, E’, SIldVercse!ner;c.“Annular gas flow : a hazard-free solution”,

2.

3.

4.

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Petrole Information, July 15, 1983, p. 34-38.

Bannister, C.E., Shuster, G.E., Woolridge, L.A.,Jones, M.J., and Birch, A.G. “Critical designparameters to prevent gas invasion duringcementing operations”, paper SPE 11982 presentedat the 1983 SPE Annual Technical Conference andExhibition, San Francisco (Oct. 5-8).

Abdel-Mota’al, A.A. “Detection and remedy ofbehind-casing communication during well completion”paper SPE 11498 presented at the 1983 SPE MiddleEast Oil Technical Conference, Manama (Narch 14-17)

Davies, D.R., Hartog, J.J., and Steward, B. “Anintegrated approach for successful primary cemen-tations”, paper SPE 9599 presented at the 1981 SPEMiddle East Oil Technical Conference, Manama(March 9-12).

Webster, W.W., and Eikerts, J.V. “Flow aftercementing - field and laboratory study”, paper- - norm -.-.---+-s ..A 1070 C’nmn.,.,,,.laPn OL3Y pL.eselll_tsu al. tk ..,2 OZx, A-U..,,4CL.

Technical Conference and Exhibition, Las Vegas(sept. 23-26).

Suman, G.O. Jr, and Snyder, R.E. “Primary cementing-..,,

why many conventional jobs rail , wor~a UIL,.. . ..

Dec. 1982, p. 59-66.

Eeir-iite,l?.%.~f.~1 -.-—--- -- -..’.--.....Aem.,.=w,Jfi~iPU.~== .=m=&&.—UUU.p=.=& ,paper SPE 5691 presented at the 1976 SPE-AINESymposium on Formation Damage Control, Houston(Jan. 29-30).

Morris, E.F., and Motley, E.R. “Oil base spacersystem for use in cementing wells containing oilbase drilling muds”, paper SPE 4610 presented atthe 1973 SPE Annual Fall Meeting, Las Vegas(Sept. 30 - Oct. 3).

x1 cRobir,s, ,..”. , =.”. ~ .M=~=*~# ;..ua y~~~p-~ ~Q

formation bonding in low-permeability argillaceousstrata”, paper EUR 367 presented at the 1982European Petroleum Conference, London (Oct. 25-28).

Yamasaki, T. , rnic’n<nilio,ii., aim xfi.an~au~,C.s “.-,._l_--L.

“Static and dynamic tests on cement grouted pipe-to-pipe connections”, paper OTC 3790 presented atthe 1980 Off-shore Technology Conference, Houston(May 5-8).

SPE 13176 Philippe PARCEVAUX - Patrick SAULT 7

11. Setter, N., and ROY, D.M. “Mechanical features ofchemical shrinkage of cement paste”, J. of Cementand Concrete Research, 1978, Vol. 8, No 5,pp. 623-634.

12.Parcevaux, P. “Pore Size Distribution of PortlandCement slurries at very early stage of hydration”,J. of Cement and Concrete Researchr 1984, Vol. 14,N“ 3, pp. 419-430.

13.Geiker, M., and Knudsen, T. “Chemical shrinkageof Portland cement pastes”, J. of Cement andConcrete Research, 1982, Vol. 12, N“ 5, pp. 603-61

14.Roy, D.M., and Langton, C.A. “Early stage hydratio!of slag cement”, J. of Cement and ConcreteResearch, 1983, Vol. 13, N“ 2, pp. 277-286.

SLURRY BONDING CURIN~ CURING AVERAQE STANDARD

DENSITY AOENT TEMPERATURE TIME SBSTRENQTH DEVIATION

glee % bvos Dog.C daym MPa %

1.901.001.901.901.901.801.901.001.901.901.901.901.901.90i.t)o1.002.102.102.101.s81.581.68

0.0$.418.80.09.418.80.0$.418.80.09.418.80.018.80.018,8

0.014.321.40.010.021.8

2020202020202020202020207070707@

707070707070

111aaa77728282811a~

aaaaaa

2.412.9a2.076.658.276.047.9a9.627.668.a612.21la.lo4.216.69a.69man----a.oo4.074.661.461.87a.m

TABLE 1. SHCARBOND STRgNQTH TEST RESULTS

9.66.27.16.11.88.81.01.9la. a18.412.62.66.117.014.0?,?

wma10.111.414.18.4a.s

CURINQ CURINQ BONDIN(i TOTAL SHRINKAOE %byvolumo

TEMPERATURE PRCSSURE A@eNT

Dog.C MPa % ●vos ●t ●.t tlmo d 24 houro ●t 40 hours

70

70

70

20

20

20

20

20

20

4.0

4.0

4.0

0.6

0.6

4.0

4.0

10.0

10.0

0.0

0.4

16.8

0.0

18.8

0.0

18.6

0.0

18.8

1.70

l.aa

O.al

a.oo

l.ao

2.00

1.80

2.00

1.40

6.00

6.20

4.80

6.20 7.16

a.lo 4.16

6.20 e.ao

a.60 4.00

4.ao 4.ao

am70 a.90

1 TABLE 2. SHRINKAOR TEST RESULTSI

[pREssuRE REwLAToRJ

Fig. I—.%h)ematicdiagramofshearbond cell.

IHYDRAULIC BOND CELL I

IBACK pREssuRE]

IM

I I

I

lpREssuRE REwLAToR]

ImImKEll

~PRESSURETRANSDUCER

/“ r

-;’ I~

\IPRESSURE CONTROLLEDANNULAR SPACEj

Fig. 2—Schematic diagram of hydraulic bond cell

rLOwER GRIo

RUBBERMEMBRANEj[0-RINGI

\

~HOLDERFOR Permeability cELLl

Fig. 2-tlolder for permeability tests.

It

la

5

00

100

so

$0

40

20

0

./-”./_/ -

_A_/

—+ 7,-/“”-./7””””//7

/

.

/

.●’

I /,*

{

q

D“

?’

,———__ ._._ ___

Legend “~

STANDARD CEMENT—— . ..

9.4 %bvoe BA.— —_ _

18.8 %bvo, BA,— ---— -.. —

~— I I I I

6 10 1s 20 25 30(cljRl~~ T~~E days

Fig. 4-Cement shear bond strength development at zO”C.

r--——Legettd

CONVENTIONAL CEMENT——

9.4 %bvog B,A——- —.— —— .

18.8 %bvoa ISA—-”” -—’ ---—-- -- I———

~~

ISHRINKAGE Cl~

[LINEAR DISPLACEMENT TRAN:-j

[CEMENT 5AMPLE -JRATED SAMPLEcHAMBERjFig. 6-Schematic diagram of shrinkage cell,

PRES!BURE DROP PER LENQTH UNIT MPA/CMFig. 5-Cement hydreulic bond curve at 70”C,

~--------- ----. ./. ----

-*.-..*

●☛

I 98.’ I 1

/tt Legend

NEAT CEMRNT

10. B %bvos DA. ------ ----

I I0 6 18 a

TIME I;2HOURSFig. 7-Cement shrinkage development at 7WC,

■

m

● ■

o ❑● Oo .

●

os 0=

s o● 0° ■

● o● 0=

●Oo g

■● Oom● 0

Legend.0=Do=0= ● STANDARD CEMENT

cl= o 9.4 %bvom 8Ar

■ 18.8 %bvos 6A

I 1 I

m

■

o●o:●00.

.00=

...O ■

■●.O.

●0po ■

■

I Legend5= ● STANDARD CEMENT

■

■ I 09.4 %bvos BAI

■ 18.8 %bvom BA

nanmmm n-n . . . . --- . -.-. —--~AUIAL ~ 1 HAIN lUE-4 GM/CM

Fig.8-Stmss-strsh ml*IOnships @f vsrious cemsnt formulations,

9

ou) I I I k*.*