7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

1/9

q

U

SPESPE 18265Recovery of Condensate From a Heterogeneous Reservoir bythe Injection of a Slug of Methane Follcwed by Nitrogenby C.A. Koseack and S.T. Opdal, The Norwegian Inst. of T. hnologyWE Msmbera

- lM . SOOWofPUmbumn@marYTM x weeprepared@rpreoenIefbnm theS3rdAnnualTeciwicalCcWemnaandExhbklonof the2ooio4yl PetrokvmEnginnrzheldIn~,Tx, Octoter2 L, lwa.Ttrlemweea1801ad krrpramwbn ~-r-dh~--tW---w4:===@---@-YdO oatained inarabMreiXeuMtfedbyth9En@neeroemdroaubjeCtbCWeOtbnaam(e).lhe~$aPra-add *YtiwEwd*wd~wd~ bytheEn@rwere,WoMoem.ofnwdem. Pqmm z~*=--@ww~-w~~ .Pemmkbniocopyis~towr~dnamofalhm~~ Mu&anmerneynotbeoo@Od w-3rIa ~ ~wt9ceandby@Iornthepeperepreamad.wrilaPuMcmbmMmew, SP&P.o.Soxm, RkhadIm, Tx7e0&%W6.Telex,- SPSOAL.

Abztr*ct cost of themethane. Economicsare givento allowone to sizea methaneslugfor a realheterogeneousTha proceaaof injectinggaa Intoa gas condensate reservoirso aa to mzxlmizethe profitof the pro-reaervoirduring productionia vftalto mdntain the ject.reservoirpressureeo that the heavyhydrocarbonfractionawfll be recovered. One wouldlike toinjecta gaa intothe reaarvoirthatia cheaperthan IntroductIonmethane,ht recentone-dimensionaltudleahaveqhewn that the injectionof nitrogenintogaa eon- The recoveryof liquidhydrocarbonsfrom a gaa con-densateat reservoirconditionswI1l resultin the densatereservoiri~ dependentuponmaintainingasloss of .!nuchf the condensateliquid. This ie a much,ofthe reservoiraa possibleas a singlaphaseresultfromthe liquiddroppingout of the gaa phaae gaa. To accomplishthisa fluidmust be injectedwhan nitrogenmixeswith the condensate.A solution into the reservoiraa condensateis producedtoto this situationis the initialinjectionof a slug replacethe reservoirvolume,maintainingthe reser-of methane(ordry gas)foilowadby the injectionof voir presuureabove the dew pointpreaaure,and tonitrogenfor pressuremaintenance. If the methane displacethe condensatetowardsthe producingwells.

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

2/9

2 RCCOVERYOF C33NWWATE FROM A RSTEROGRNEOUSRESERVOIR ET TRE INJECTION OF A SLUG

.4SPII ia265

Mzing large quentltieaof expeneivemethane(dry initialcondensiateaew point,theseeimulati~na@ or withoutloeeof condensatewhen nitrogenie provideoptimisticrecoveriescomparedto preesureused? A poaaiblesolutlon,studiedin this depletionproceseor only partialpreseuremein-research,ie the initialinjectionof a smellSIUS tenenceproceaawhere condensaterecoveriesareof methanefollowedby the injectionof nltrosenfo~ generallyin the rangeof 20% to 30%1$6.preesure-intenence and aa a drive flu%d. The -theorysays that themethaneslug buffersor separa- A syntheticcondensatewse used consistingof aixtes the condensatefrom the nftrogenduringthe component, Cl, C2, C3, C5, C6 and C1O. A publisheddisplacementprocess. Withoutthe mixlnsof nitro- phesemetch7wee usedas pre8entedin the one-Ben and condensate,the processremeinesingle dimensionalsimulation. Am describedby Koseacketphaee. In realttythisdisplacementproceesl ike al (Fi&ure5)2,allmixturesof this condensateandotherslug displacementprocesses3is controlledby methanehave dew pointsbelow3000 peia (200bar) atreservoirheterogeneltiea,hich (1) are the sour= 1600F (72C). On the otherhand the dew pointsofof dispersion,(2) causebypassingand (3) initiate mixturesof nitroDenand the condensateriseveryviscousfingering.To evaluatethis eltuationthe rapidlyas the nitrogenmole fractionincreasesfromdisplacementof condensateis modellednumerically zero. Thus,a mixturewith a nitrogenmole fractionin a three-dimensional,ully,compositionalreser- greaterthan approximet j .05willhave a dew pointvoir simulatorwith variousslug sizesof methane grastarthan 3100 paia {213.8bar).rnndfour differentlevelsof reservoirheteroge-neity.

~ene~t~ea and ~oh~cal LeyerfwzNumericaland FluidModels In an idealdisplacementin s homogeneousreservoir. free of disperaton,densityd~fferencea,and mobi-To accuratelysimulatethie complicatedcom- litydiffarances,an infinitesimallymallslugofpositionalp rocess , a fully compositionalreeervoir methanewill separatethe n i t rogen from the conden-simulatorwea needed. A2S0 to keep numerical sate and the resultingrecoverywill be the s am e s edispersionto qn acceptable,low leveland to pro- the continuousinjectionof methane. In a re a lvide a sufficientnumberof pointsto describethe three-dlmenehnelreservotrcontainingreal fluidereservoirhete.ogenslties,000 grid blockswere the recoveryis controlledby mobilitles,densities,used in the three-dimensionalusrtarfivespot, dlsperstonand geology. Dispersionrefersto thefhesocelculationawere made on the NorwegianIneti- mi~ingof fluideby microscopicand perhapetuteof TechnologysCRAYX-t4P/2Ssing the MOKE* macroscopicheterogeneities~ithina geologicalEquationof Statecompositionalreservoir layer. The m?xingcausedby permeabilityvariationsslmulator4. Each simulationcase required5 to 10 betweenlayers%s calledmacroscopicor glgaecopicminutesof CPU time. diepersicutdependingon the size cf the iayers).For theseemulations numericaldispersionwas usedThe flowfieldwas a quart%rof a fivespot. The to approximet~the physicalJisperaionpresentoveralldimensionsof 1000 feetx 1000feetx 50 insidethe geologicallayers. By using8000 gridfeet (304.8x 309.8x 15.24reters)were subdivided blocks,the numericsldispersionand, thus,the sub-intoa 40 x 40 x 5 grid. Ar injectorwas completed geologicallayerdispersion(or sometimescalledin all five layersin one c(rnerof the grid. The sub-gridblockdispersion)was kept to abottomhole pressure(BHP)of the injectionwell was reasonablelevel.set to 3100psia (206.6bar). This controlledtheamountof gas injection.The BHP was 148 psia (9.9 To quantifythe amountof numericaldispersionin

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

3/9

BFX 18265 C.A. KOSSACK AND S.T.OFDAL 3r ese rvo i r whichffte Lya et cls correlation. Homogeneous- GridAEhue,themixingof fluideinsidethese25 x 25 x 10Eeet (9.6 x 9.6 x 3.0 m) blockscaueedby numerical The resultsfrom the homogeneousdescrfptfon,Figurtieffectsia wall withinthe mixingfoundin normal 5, are shown for both the isotropiccaseheterogeneousreservotrrock. (kv/kh= 1.0) and an anisotropiccaae (kv/kh=O.O1).The continuousinjectionof nitrogen racovera onlyAlsosincethe samegridwas used for all the simu- 64% and 67% of the condensate(isotropicand ani-mationsthe amountof mixingwould remainapproximz- eotropic,respectively).This ie the effectoftely constantfrom case to case. fhus,the mixingin the sub-8rldblock (sub-geologicalayer)differencein recoverybetweentwo geological scale. As the amountof buffermethaneis increaseddescriptionscan be, for themoat partaattributed the recoveryIncreasesto a maximum of 83% to 85%.to the effectof the geologicallayering. Actuallythe continuousinjection,f methane(pointson the far right)ahow a decreaaeIn recoveryfromRaaervoirheterogeneitiesere put Into the descrip- tbatof a 100%PV slug followedby nitrogen. Thetion in the formof permeabilityvariations. When a aniaotropicresultsshow that croesflowingofgeologicallayeris defined,whetherit has the size fluidsin thiehomogeneousreservoirdecreaaeatheof one gridblockor 1600Sridblocks,a singleran- recovery.dom valueof a permeabilityis put into the layer.Fhus,the layerts homogeneous.Permeabilitieearensatgnedto the layeraby a randomnumbergenerator RandomlyHeterogeneous- Grid Bwhich draws parmaabilities froma log-normaldistri-bu t ion with a mean of 500 MO and a Dykstra-Paraons When additionalmixingla addedto the descriptionCoefficientll,, equal to 0.7. The use of random by theway of 8000 randompermeabilityvalues,thepermaabilitiearequireethe generationof several recoveryfor pure N2 Injectiondecreaaesto approxi-realizationsof the reservoirand the applicationof mately60%, Figure6. The threecurvesthatareUomteCarlosimulat%onato bee t h e e ffe ct of the ehown are from different realization. Littlesen-raalizattona.When only a few parmeabllityvalues eitivityis seen to the assignmentof the 8000qre qsstgnedto the grid creatinglargegeological values. The continuousinjectionof methanereco-layera,many realizationsre required to completely vered 83% to 84% of the condensate as was the casestudy the aanaitivtty to the randomprocees. For in Grid A. The effect of kvfkh 18 qxplored inthis paper, economic conaideratlomelimitedthe Figure7 for seed2. Here crossflowingla not aumber of raalizetions made. Three different aignkftcant factor.heterogeneous geological discript%ona qnd one homo-gemeoue diecriptlonwere createdfor this study.Theeedescriptionsspan only part of the aet of LargeNaterogcneities Grid Cpoesibleor probable geological situations. When 40 largeheterogeneitiesre put into the gridThe oimplestgeologicaldescription,Figure1, (Grid the additionalmixingand macroscopicbypaseingofA, below)is homogeneousand isotropic,kx = ky = oil In low permeabilitylayersreducesthe recoveryk=. IIerethe effect of the sub-geological layer from that of gridsA and B for all casea, Figure8.dispersion(numericaldispersion)is the only source The recoveryfor continoust42injectionrangesfromof mixing. 45% to 58X. For continuousmethaneinjectiontherecoveries,comparedto gridsA and B, drop to aGrid B (Figure2) consietsof 8000 smallgeological rangeof 76% to 84%. The effectof the aet of 40layers25 feet by 25 feet by 10 feet(9.6m by 7.6 m randompermeabilitieschosenhave a largeeffecton

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

4/9

q

4 itt?COVERYF CONDENSATEFROXA NBTE80GENEOUSSESERVOIRST lMS INJECTIONOF A SLUG SP8 1826568%. This %mdicatee q gravity werride of theinjected geeee.

Effect of GeologicalIayerLengthA croee-plotof theeereeultsshovethe effectofthe geologicallayerlengthon the recovery,Figure11. The abeciseaie plottedas the ratioof thelengthof the haterogeneity(layer),& to thelengthof the eyetem(wellto well),L. Thie ratio,&L,ie sometimereferedto ae correlationlength.The reeultsof injectingcontinuousN2, a 10%, and50% methaneelugand continuousmethaneare plottedfor comparativepurosee. The resulteare theaveragerecweriee for all the isotropic realiza-tion performed whichtotalednearlyninty,three-diaeneionaldisplacements.In come caeee,espe-ciallygrid D, a largernumberof raalizationeisprobablywarranted,thus,the valuesplottedinFigure 11 couldvary eomewhetif more realizationswere included. The followingobimrvatloncan bemade:

- Fo: re N2 or a mall ~thane sluginjectionqold..onalmixingie causedby the smallscaleheterogeneities,S/L = 0.025, reeultixgin alose of condensate.

- For pure N2 or q eadl methane slug injectionthe recovery increeeee as the correlationlength, S/L, increesee froz 0.5 to 1.0,bacauee of the low eeountof mixing in thelarge homgeneoue layers.- With a 50% slug of =thaae or pure methaneinjection,the additionof 8000 eaallheterogeneities to the homogeneousgrid, (E/Lincreasingfrom0.0 to 0.025),actuallyinproveche recoveryover the homogeneousreservoir. Thie is due to the effectofincreasedtranfiverseixing (dispersion)onthe displacementin an adversemobilityratio-misclbleprocess.

$011COet (saleeprice) of on e STBof oil$c~ = Costof NBCF of aethane(usageand lose)$N2 = Coet of one XSCF of nitrogen(at the wellhead)Ss - Slugsize of methaneinjectedPv - Porevolumeof reeervoir in N8CF

$Cl is the leesof money incurredby the injectionof methane. When methanela injectedfntothereeervoirit can not be sold for 2-4 yearewhileitie underground.Thue part of $Cl ie t ha loetintereston the mney one would=ke (duringthisperiodof time)if the methane was sold. Anotherpar t of $Cl comes from the factthat 100%of theinjectedmethaneis neverproduced. Therefore,althoughthepriceof methaneis between$ 2-3/M3CF,the lose o# moneyby injectingmethanewea estimatedto be $.85/NsCF.For thisstudythe cost of nitrogenproductionwasestimatedto be $ .25/N8CFand the valuaof the con-densateliquidwas set at $ 20.00/sTB.The basicdata that produced the recovery of money plot,Figure 12, are provided in Table 3 for situationswhere the coate ($Oil, $Cl, $N2) are significantlydifferent than those qtated above. Again the econo-mical calculation were made with the recoveriesaveraged free the ieotropic realixatione. Aleo note(1) that no calculations were-de for grid Dat aslugsize of 0.05, and (2) the additional cost ofpurifyingfluidein the presence of H2has not beenconsidered. The following observations can be madefrom Figure 12:

- A 5% PV slug of methanemskaeaoneyin alltypesof reeervoir. In fact thisie near themaximumrecoveryof money for the homogeneousreservoir(GridA) and the smallheteroge-neity,t/L = 0.025,caee (GridB).- For the largeheterogeneityreservoir(GridC)a 10% slugof methanethe recoveryof moneyhas a maximumvaluesof nearly$ 60,000(recallthis is from a quarterfivespot).

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

5/9

SPt 1826S C.A. KOSSACKANDS.T. OPDAL 5councilScienceand the It um m it ie s (NAVF) an d fromthe Nordiak Induetrifond.

Keferencee1. Moses, P.L. end Wilson, K.: PhaseEquilibriumConsiderationsin UtilizingNttrogenforImprovedRecoveryfromRetrogradeCondensateReservoir,SPE 7493,presentedat the SPEDHoueton,Te xa a, Oc t . 1-3,1978+2. Koeeack,C.A., Opdal,SOT.,Hagen,S. andHunkerud,P.K.:Experimentaland Theoretical

Investigationsof Gee Injectionintoa Gee Con-densate,Proceeingef 4th EuropeanSymposiumor EnhancedOil Recovery,27-29October1987,Namburg.3. Koeeack,C.A.and Bilhartz,li.L.:TheSen-

qtlvlty of HicelleaFloodingto ReeervoirIieterogeneitiea.PE 5808 Preeentedat theImproved0%1 RecoverySyapoeiumof the SPE,Tulsa,OK, March 22-24,1976.4. Young,L.C.:%quetion of StateCompoeitLonalNodelingon VectorProce$eors, SEW 16023,Pre-qented qt the Ninth BH Sympoelum held in BenAntonio, Texas,February1-4, 1987.5. Kenyon,D.E.,and Behie , A.: 1 b ir d S PE Com -parativeBolutlonProject:Gas Cyclkngof

Ketrosrde Condensate Reeervotre. Roceedingeof the Seventh SympoaiI= on Kaservoir Sibila-tion,sem lhncisco, Nomber 15-18,1983.6. Clancy,J.P.,Gilchrist,R.E. , ltroll, .E . qndNecGregor,A.: Improved011 and Gee RecoveryUsing NitrogenLaboratoryAnalyaieCaueeandEcono?eice.Proceeding 3rd EuropeanSymposiumOn ImprovedOil Recovery,Rome (1985)255-264.7. Koaeack,C.A.,Ragen,S. and Munkerud,P.K.:PhaaeBehaviorCalculationsNear tha Critical

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

6/9

SPE 18265

o

0

o.0

v

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

7/9

50

1 /71eet A4 b

1000 feetFig. lHoIT~nOOUS geology-Grid A.

tI/-= ,,= I

Fig . 2-mt911y hoto~ B(achIsl grhh40x40xs).

tl/ II

Fig. 3Lsr9s hstsrogene ities-Gr id C. Fig. b@W heteroganeitio+md D.

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

8/9

al

85-

80 .....

fa (:653~60-8~ 5550 45 1 1 10.00.1 0.20.30 .40.50.60.70.8 0.9 10S iZJ ? !OF C, SLUG INJ ECTED(POREVOLUMES)

8580

g 75 Fd .. (z 11...G 76 -k

uW* a -+ Iz&= 1.3_50

%0 0.10.20.30.40.50.60.7 0.80.91.0

8580

~ 75~h

j 5550

%0 0.10.20.30.40.50.60.7 0.80.91.0SIZE OF Cl SLUG INJECTED(POREVOLUMES)nb~vOldbmm uB@Mv MWwmm WW8u .9mmm** .

85 1 I=- SEED3 .,----80 - e SEED2 ~ y -- -, , ---- ---+ sEJ IDl q* -o dy :, L je t .ed -~ 7 5 ~ ,- ). . / ~ ......~ / ,....0 70 - 3 w - ,.....q,08

0g 55

0.1 0.20.30.40.50.60.70.8 0.9 10SIZEOF C, SLUG INJEXXED(POREVOLW)

(nmm

7/27/2019 SPE 18265 Recovery of Condensate From a Heterogeneous Reservoir by the Injection of a Slug of Methane Followed by Nitrogen

9/9

85 .80 ...--

g 75 ~d070k065isu

.30.40.50.60 .70.80.9 1.0SIZR OF Cl SLUG INJ ECTED(POREVOLUMES)

85 ~t .8 0 % -. ,. .- - --- .-

.. .t -....- --- .- +--- . -~ 7 5 .. . . . . . . . . --. . . . . . . . . . . -. -. . .. . . . .k;60 $g 6 00ur&5 5 / )5 0 N.

4% 0 0 . 1 0. 2 0 .3 0 . 40 . 5 0. 6 C,7 0.80.9 1.0(LENGTH OF HET.)/(RESERVOIR IENGTH)~tHhavq#dImmtmdti-=$W-W

85- -L L- [-+ EEED-4 !8 0 - -* S EED 3.O S2 2D 2

g 75 -~07 0 - ...........,...... ...... ....... .....&

u . ~ly ~ , ~ ]ec t ea - -

5 d4 ~o 0 1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1 .0

. S IZE OF c1 SLUG INJ ECTED (PORWOLUMES)

60000 I IMA -..-WI.......40000 . P.. \/ . %. .. . >f.....\ - %.. .o ---- -------- ~ .> .%>-20000 ... .-40000

-80000 ..... G~ BGRIDA.- _- looo~.oo0 .0 5 0 .1 0 0 . 15 0 .2 0 0 .2 5

(n-0m