screening of oil reservoirs for gravity assisted gas injection.docx

7/25/2019 Screening of Oil Reservoirs for Gravity Assisted Gas Injection.docx

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SPE 39659

Screening of Oil Reservoirs for Gravity Assisted Gas InjectionB. Lepski, University of Alberta, Z. Bassiouni, Louisiana State University, J.M. Wolcott, FIASolutions

Copyright 1998, Sodoty of Petroleum Engineers, Inc.

This paper was preparad for presentaron at the 1998 SPE!"E Impro#ed "il$eco#ery Symposium held in Tulsa, "%lahoma, 19&'' (pril 1998.

This paper was selected for presentation )y an SPE Program Committeefollowing re#iew of information contained in an a)strae* su)mitted )y theauthor+s. Contents of the paper, as presented, ha#e not )een re#iewed )y theSodety of Petroleum Engineers and are su)-ect to correction )y the author+sThe material, as presented, does not necassarily reflect any position of theSociety of Petroleum Engineers, its officers, or mem)ers, Papers presented atSPE meetings are su)-ect to pu)lication re#iew )y Editorial Committees of theSociety of Petroleum Engineers, Electronic reproduction, distri)ution, or storageof any part ofthis paper for commercia* purposes without the written consent ofthe Society of Petroleum Engineers is prohi)ited. Pormission to reproduce inprint is restricted to an a)stract of not more than // words0 illustrations maynot )e copied, The a)stract must contain conspicuous ac%nowledgment ofwhere and )y whom the paper was presented. rite 2i)rar3an, SPE, P.". 4o5886, $ichardson, T7 /8&86, :.S.(., fa5 /1&9'&9'&9;.

AbstractCorefloods and field investigations confirmed thatincremental oil can be recovered from dipping water-drive reservoirs using gravity assisted gas injection

processes such as Double Displacement Process(DDP), and Second Contact ater Displacement(SCD)! "ransparent cell e#periments support the

presumption of film flow of water-displacement-residual oil and the dependeney of these methods$efficiency on fluid distribution within the pore space!"he ability of oil to form a film is %uantitativelye#pressed by the spreading coefficient defined in termsof interfacial and surface tensions of the phasesinvolved!

"he drop volume and pendant drop techni%ueswere adapted to provide rapid and convenient methodsfor the measurement of &'" at high-pressure and hightemperature conditions! "he interfacial and surfacetensin properties of several fluid systems wereinvestigated!

&'" measurements of systems used in the core-floods support the belief that a positive spreadingcoefficient is needed for an efficient recovety ofresidual oil! &'" measurements proved also thatinjection of nitrogen is more beneficial than methane tothe creation of an oil film that Controls incremental oilrecovery efficiency!

"he simplicity of the adapted &'" setup, combinedwith its ability to perform a large number ofmeasurements, may result in the development of anempirical screening criteria needed in the selection ofreservoirs suitable for DDP and SCD processes!

Introduction"he Double Displacement Process (DDP) involves up-

dip gas injection in a water-invaded oil one in order tomobilie and produce incremental oil*! "he incrementaloil results from the difference in residual oil saturationin the presence of water as compared to that in the

presence of gas! +ravity stable displacement causes theformation of an oil ban which collects oil as itmigrates downward in the reservoir towards the

producing well! simplified schematic of a DDPcandidate reservoir is shown in 'ig! *! .nder favorablereservoir conditions, incremental oil on the order of/01 of the initial oil-in-place may be recovered usingDDP! "he schematic of the reservoir subjected to DDPis shown in 'ig! 2! hen conditions are favorable, theduration of the DDP may be shortened by introducing

Second Contact ater Displacement (SCD)! SCDis an e#tensin of the DDP and in principie gasinjection is followed with down-dip water invasin,

preferentially from a strong water a%uifer! Schematicillustrating the SCD is shown in 'ig! 3!

&n order to recover water-displacement-residualoil, we must restore its effective permeability! 4y

injecting gas, water is displaced from pores where oilglobules are trapped! 'or initially water-wet systemscapillary forces cause oil to spread between the watercoating the pore wall and the gas bubble occupying thecenter of the pore! "his creates conditions for film-flow

reconnecting the oil in the gas invaded one! "hereconnected oil flows downward due to gravity forcesand creates an oil ban! 5il gravity drainage process iscontrolled by fluid density difference, reservoir dip,fluids viscosity, and oil effective permeability

DDP has already been tried in several fields andyielded promising results! "he ees &sland field DDPwith C02 and methane was completed by Shell2! "he6awins 'ield DDP nitrogen injection project operated

by 7##on*,3, and the est 6acberry DDP air injectionproject operated by moco are currently in progress/! new process conceptually similar to SCD wasimplemented in 4onnie +len reservoir operated by&mperial 5 i l !

Reservoir Screening riteria"he DDP and SCD can be economical 758 methodsfor reservoirs with substantial oil left after waterinvasin, assuming suf'icient permeability, bed dip andoil viscosity for gravity drainage! 4ased on a numericalsimulation study, a good candidate for DDP shouldhave permeability of 300 md or more and dip angleover *0 deg! "he study showed that lower permeabilityhas more detrimental effect on process efficiency thanlower dip angle9!

:umerous investigators pointed out the role offluid distribution within the pore space! "he

phenomenon called spreading coefficient was found to

control both gas displacement efficiency and threephase oil and gas relative permeabilities;$S'o w=final spreading coefficient of oil over water,m:?m awg@ water - gas interfacial tensin, m:?mcr0g@ oil - gas interfacial tensin, m:?m cxow@ oil- water interfacial tensin, m:?m!

hen S'uwis positive, oil tends to spread on waterand form a continuous film! hen S'(lis negative, oildoes not spread on water!

Several investigators reported that highest oilrecoveries in water-wet media were observed for

positive S'ow fluid system**,*2! Aower oil recoveries inoil-wet media were attributed to capillary retentionforces! "here was no detectable difference between

positive and negative SBo?w fluid systems in oil-wete#periments**! 4oth drainage and imbibition oil relative

permeabilities were higher for positivespreading

coefficient*2

!"he spreading coefficient is the ey to thefeasibility of the DDP! 8epresentative vales ofinterfacial tensin between each pair of fluids involvedare needed to estmate the spreading coefficient!


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!" #$ %EPS&I' ($ #ASSIO)*I' +$,$ -O%O.. 39659

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Interfacial .ensi0n&nterfacial tensin (&'") results from imbalance ofmolecular forces at the interface between two dissimilar

phases! Commonly, the term interfacial tensin is used todescribe the tensin at a li%uid-li%uid interface while surfacetensin refers to the tensin between li%uid and gas! "he &'"is the forcE per unit length re%uired to increase the area of

the interface by one unit! &t is usually e#pressed in dynes?cmor m:?m which are numerically e%ual!

&'" is measured using a number of methods such asilhelmy Pate, Du :ouy 8ing, Capillary 8ise, SessileDrop, Spinning Drop, FG#imum 4ubble Pressure,5scillating Het, Drop Iolume (or weight), Surface aves

and Pendant Drop! Since &'" measurements re%uired by thepetroleum industry often involve high pressure and hightemperature (6P6") conditions, the Pendant Drop method ismost widely used! nother method, Drop Iolume, which isnot yet available for 6P6" was investigated as a part of thisresearch and yielded promising results for 6P6" &'"measurement applications!

&n Pendant Drop method, a drop hanging from acapillary tip (or a clinging bubble) elongates as it growslarger! "he drop shape is used in calculation of the &'" *!

&'", oJ, can be calculated %uicly using followingalgorithm*9>

a =ApgR02//3 (2)

yK@0!*2

Interfacial .ensi0n ,easure1ents )nderReservoir onditions&'" measurements needed for spreading coefficientcalculations have to be performed under reservoirtemperature and pressure conditions! 8epresentativereservoir oil phase was obtained by recombining oil and

methane! "hrough indow 8usa PI" Cell Fodel 232=-

'or pendant drop &'" measurements, the high pressure8usa PI" Cell was adapted to accommodate a detachablecapillary! &n our case, a 22 gauge (2!0=LL mm 5D) syringeneedle, which was cut and polished to obtain a fat top wasused! "he capillary mount was made from a standardsurgical Steel syringe connector cut out from the syringeand screwed on a piece of *?


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39659 SREE*I*G O2 OI% RESEROIRS 2OR GRAI.4 ASSIS.E GAS I*+E.IO* !!

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fluids! "he schematic of the capillary housing is shown in'ig! =!

"he sie of the capillary was similar to the siestypically used for &'" measurements performed by the oilindustry2 ! "he selection of the capillary sie and resultingdrop sie was also determined by the sie of the window ofthe 8usa PI" cell (9!3L mm wide)! Depending on the

measured fluid system density difference, the capillary wasmounted in the top or in the bottom of the PI" cell asshown in 'ig! *0! Since the drop had to be visible, thecontinuous phase had to be transparent!

Pendant drops were formed by injecting thediscontinuous phase at a very slow, constant injection rate,(lcc?hr) to avoid &'" changes due to aging time differences!"he videotape frames containing an image of the hangingdrops were captured, saved as bitmaps and laterdownloaded into the measurement software!

"he measurements were performed using theuncalibrated pi#el option to speed up processing! Distancecalibrations and &'" calculations were later performed usingspreadsheet Computer application! Distances were

calibrated using the outer diameter (5D) of the capillary!"he 5D was measured within 0!00 lmm accuracy using amicrometer!

Drop volume &'" measurements were made bypumping the light phase into the dense phase at a slowconstant flow rate! Drops formed at the tip of the speciallydesigned capillary, and the volume of the drop wascalculated from the injection rate and the number of dropsformed within a specifc time period!

"he drop volume &'" measurements were performedusing the same setup as for the Pendant Drop measurementswith the positive displacement pomp used for li%uidinjection! helical-shaped spiral of about /0 cc was usedinstead of the 2L0 cc transfer vessel used in the PendantDrop study to minimie flow rate instabilities due totemperature fluctuations! Since the drop sie was small, inthe range of 30L0 WiA, fluid volume changes were able tocause flow rate fluctuations when large volumes of li%uidwereX involved! gain, distilled, degassed water was usedas driving fluid with the L0Y ppm YC* brine used as buffer

between measured sample and driving fluid! &njection ratesvaried from * cc?hr to / cc?hr depending on the sie of thedrop! &n order to seal the tip at elevated temperature, themanufacturEis leaing "eflon fltting was replaced with astandard *?*9V Swagelo steel fitting screwed on the top of*?*9V-*?

published vales*;! &n all cases, e#perimental vales obtainedwith pendant drop setup were within L1 range from the

published vales! comparison of measured and publishedvales is given in 'ig!

*/! "he summary of &'" measurements performed fore#perimental coreflood fluid systems is given in"able *! "he resulting spreading coefficient valesare given in 'ig! *L!

&n addition to spreading coefficient measurements,surface tensin measurements of L0 Y ppm :aCl brine in

presence of methane and nitrogen were also conducted!Selected pressure settings were *L00, 2000, 2L00, 3000,3L00 psia and temperature settings of L2!L, 99!


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!" #$ %EPS&I' ($ #ASSIO)*I' +$,$ -O%O.. 39659

*0= and *29!< C! "he reason for these measurements was toestablish some guidelines to estmate surface tensions of

brine in presence of two gases commonly used for gasinjection gravity assisted processes! "he practicaZimplications of the results are presented in 'ig! *9 and *;!

Drop Iolume method was initially considered for &'"measurements but was later abandoned in favor of Pendant

Drop method mainly due to inabiiity of surface tensinmeasurement using Drop Iolume method! "his is true underambient conditions for which the Drop Iolume method wasdesigned! hile investigating li%uid?li%uid interfaces, it wasobserved that gas bubbles formed under high pressure

behave as drops of li%uid! "his idea was pursued further andsurface tensin measurements for :itrogen at 99C and=9C were performed using drop volume method for thesame pressure points as pendent drop measurements!.nfortunately, using standard method of drop siecalculation based on injection rate and number of dropsformed during a time period was not possible because evenminor temperature changes resulted in some injection rate

instability! Since this was a conceptual study, a simplifiedimage processing was used instead, assuming sphericalshape of the drop for &'" calculations! "he comparison ofthe Pendant Drop measurements and Drop Iolumesimplified image processing results are shown in 'ig! *< and*=!

&nterfacial tensin measurements indicated that all fluidsystems used for e#perimental corefloods had positivespreading coefficients! "hat indicated that oil mobiliationshould have occurred through film flow after gas injection!'rom the correlation measurements for water-nitrogen andwater-methane systems, it was concluded that higher watersurface tensions will be observed for nitrogen as comparedto methane! "he difference ranges from about *0 1 for low

pressures and temperaturas up to about 20 1 for the highestinvestigated pressures! 6igher water-gas surface tensinshould benefit film formation provided &'" of other phasesremain the same! Clear trends were observed forwater?methane surface tensin in ranges of the pressures andtemperaturas studied! :o such trends were observed forwater?nitrogen surface tensions!

Iales of surface measurements for water-nitrogensystem performed with Drop Iolume method were found to

be about 301 smaller than vales obtained with PendantDrop method! 5ne possible reason for this discrepancy is thesimplified image processing techni%ue used for drop siecalculation assuming spherical shape! nother source of

error seems to come from compressibility effect and theprecisin of fluid density data! "he effect of compressibilityseems to be more evident in 'ig! 20 where Pendant Dropvales of &'" were crossploted vs! Drop Iolume vales!'urther investigation of Drop Fethod surface-tensionmeasurements was not attempted since it is beyond thescope of this research!

onclusions&nterfacial tensin measurements indicated positivespreading coefficients for all performed 6P6" e#periments!'rom e#perimental measurements it was also found thatinjection of nitrogen yielded a more beneficial spreadingcoefficient because water?gas surface tensin was higherthan that of methane! "he difference in &'" was estimated to

be in the order of *0-201 within the range of investigatedconditions!

"he simplified pendant drop method was found to besufficiently accurate for initial reservoir screening based onspreading coefficient valuE! &nitial results obtained with dropvolume method promise the development of altemativemethod of &'" measurements under reservoir conditionsalso applicable for measurements of interfaces between non-transparent li%uids! &n addition, strong correlation betweendrop volume and pendant drop water-gas surface tensinwas obtained for high-pressure gas systems! "his may leadto development of a new method of surface tensinmeasurement for high-pressure systems!

Ac7no8ledg1ents"he financial support provided by moco and the .!S!Department of 7nergy is thanfiilly acnowledged! Specialthans are e#tended to Fs! Sara Shayegi for her constanthelp and assistance during the e#perimental wor performedin the AS. 7nhanced 5il 8ecovery laboratory!

References*! Carlson, A! 5!> XPerformance of 6awins 'ield

.nit .nder +as Drive-Pressure Faintenance5peration and Development of an 7nhanced 5il8ecovery ProjectX, paper SP7?D57 :o! *;32/

presented at the SP7?D57 7nhanced 5il 8ecoverySymposium in "ulsa, 5lahoma, pril *;-20,*=2! Hohnston, H! 8!> Xees &sland +ravity Stable C02PilotX, paper SP7?D57 :o! *;3L* presented at theSP7?D57 7nhanced 5il 8ecovery Symposium in"ulsa, 5lahoma, pril *;-20, *=3! Aangenberg, F! !, 6enry, D! F!, Chlebana, F!8!> XPerformance and 7#pansin Plans for theDouble Displacement Process in the 6awins'ield .nitX, paper SP7 :o! 2 X"he use of ir&njection to &mprove the Double DisplacementProcessesX, paper SP7 :o! 293;/ presented at the9 ["he SuccessiveDisplacement Process> 5il 8ecovery During4lowdownV, paper SP7 39;*= presented at the


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*==9 SP7 nnual "echnical Conference and7#hibition, Denver, C5, 5ctober 9-=!

9! 4ensaid, '!> [7ffects of Dip ngle, bsolutePermeability and 8elative Permeability on theDouble Displacement ProcessV, "hesis, AS.,4aton 8ouge, *==L!

;! Yantas, !, Chatis, &!, Dullien, '! ! A!>X7nhanced 5il 8ecovery by &nert +as &njectionX,

paper SP7?D57 :o! *;3;= presented at theSP7?D57 7nhanced 5il 8ecovery Symposium in"ulsa, 5lahoma, pril *;-20, *= X8ecovery ofaterflood 8esidual 5il by +ravity ssisted &nert+as &njection .sing a 6oriontal ell in a "wo-

Dimantional reservoir FodelX, paper PetroleumSociety of C&F \ 5S"8 :o! =/-/= presentedat /Lth nnual Feeting in Calgary, CaTada, Hune*2-*L, *==/!

**! Iiia, 5! and Aombard, H-F!> [ettability andSpreading> "wo Yey Parameters in 5il 8ecoveryith "hree-Phase +ravity DrainageV, S%&R&('ebruary *==9)!

*2! Yalaydjian, '!H-F!, Foulu, H-C!, Iiia, 5!, andFunerud, P!Y!> ["hree Phase 'low in ater-etPorous Fedia> Determination of +as?5il 8elativePermeabilities .nder Iarious Spreading

ConditionsV, paper SP7 299;* presented at the*==3 SP7 nnual "echnical Conference and7#hibition, 6ouston, "U, 5ct 3-9!

*3! damson, !!> Phvsical Chemistrv of Surfaces!Hohn iley and Sons, :ew ]or (*= XPendant Drop"echni%ue for Feasuring Ai%uid 4oundary"ensinV, Sur+ace a$d ollod Sce$ce,Hohn iley

\ Sons, :ew ]or (*=;=) =3!

*9! 6erd, F!D!, Aassahn, +!D!, "homas C!P!, 4ala+!!>X&nterfacial "ensions of FicrobialSurfactants Determined by 8eal-"ime Iideo&maging of Pendant DropsX, SP7?D57 :o! 2/209

presented at the SP7?D57 7ight Symposium on7nhanced 5il 8ecovery in "ulsa, 5lahoma, pril22-2/, *==2!

*;! +ilman, A!4!> X 8eview of &nstruments for Staticand Dynamic Surface and &nterfacial "ensinFeasurementX, Presented at the 5CS nnualFeeting and 7#po, naheim, C pril 2;, *==3!

*

20! Hennings, 6!]!, Hr! and :ewman, +!6!> V"he 7ffectof "emperature and Pressure on the &nterfacial"ensin of ater against Fethane-:ormal DecaneFi#turesV, 1ra$ &F7 (*=;*) 24,*;*-*;L!

2*! 6ocott, C!8!>V&nterfacia& "ensin 4etween aterand 5il .nder 8eservoir ConditionsV, 1ra$,&F7 (*=3=) 432, * "he Properties of Petroleum'luids! (Second 7dition), Pennell 4oos, "ulsa*==0!

23! D!4! 8obinson Design \ Fanufacturing Atd!>Product?Services +uide! 7dmonton, CaTada, *==9!

2/! Aepsi, 4!> [Physical Fodeling of 5ilDisplacement by +as in ater 'looded ^onesV,"hesis, AS., 4aton 8ouge, *==L!

2L! Aepsi 4!, 4assiouni ^!, olcott H!> XSecond-Contact ater Displacement 5il 8ecoveryProcessX, SP7?D57 3L390 in proceedings of theSP7?D57 "enth &mproved 5il 8ecoverySymposium, "ulsa 5Y *==9!

29! 4eggs, 6!D!> Production 5ptimiation .sing:5DA_


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;! +as 7ncyclopedia! 7lsevier Publisher, :ew ]or, *=;9! ```

2 Aange$s 6andboo of Chemistrv! ("hirteen

7dition), Fc+raw-6ill 4oo Company, :ew ]or,*=


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screening of oil reservoirs for gravity assisted gas injection.docx

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