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Phase-Behavior Properties of C02-Reservoir Oil SystemsRALPH SIMONMEMBER SPE-AIMEA. ROSklAht CHEVRON OIL FIELD RESEARCH CO.ERDINC ZANA LA HABRA, CALIF,MEMBER ?PE-AIME

ABSTRACTThis paper presents experimental phase behavior

data on two C02-reservoir oil systems at reservoirpressures and temperatures.

The duta include(1) pressure-composition diagramswith bubble poizts, dew points, and cntical points;(2) vapor-l iquzd equilibtiurn compositions and relatedK values; (-3) vapor and liql,~d densities comparedwith values ca[culat ed by tb e R ed[ich- Kwongequation of state; (4) vapor and liquid viscositiescompared with predictions by the Lohrenz-Bray-Clark correlation; and (~) interracial tensions forsix vapor-liquid mixtures compared with valuescw/cu Iated by the Weinaug-Katz paracbor equation,

These and other published data contribute todevelopment of th~ generalized correlations neededby reservoir and production engineers for evaluating,designing, and efficiently operating C02 -injectionprojects.

INTRODUCTION

,This paper presents experimental phase behavior

data for two C02 -reservoir oil systems. These dataare used in predicting the performance of C02 floodswith a compositional simulator. The simulatorcalculates vapor and liquid compositions, densities,viscosities, and interracial tensions to describe thephase behavior as the injected C02 advances throughthe reservoir, The simulator predictions are used toevaluate proposed projects and to design andefficiently operate approved ones.The data in this paper consist of prcssure-

composition diagrams with bubble points, dewpoints, and critical points; and compositions,densities, viscosities, and interracial tensions ofvapors and liquids in equilibrium in the two-phaseregion. These data were obtained by the experimentalprocedure shown in Fig. 1.We have compared our measured data with valuescalculated by existing methods: Redlich-Kwong

Original manuscript received InSociety of Petroleum EnKineersoffice Jan. 14, 1977. Paper accepted for publication Aug. 15, 1977.Re .ised manuscript received Sept. 21, 1977. Paper (SPE 6387)was presented at the SPE-AIME Permian Basin Oil and GasRecovery Conference, held in Midland, Tex., March 10-11, 1977.0037/9999 /7 S/0002-6387 $00.2S@ Society of Petroleum Engineers of AIME20

equation for densities, Lohrenz-Bray-Clark corre-lation for viscosities, and the Weinaug-Katzparachor equatim for interracial tension. We foundthat these published methods give acceptableagreement in some areas, but in general, they arenot satisfactory for engineering purposes. Therefore,we conclude that improved calculation methods areneeded for C02 systems. For the special case ofcompositional simulator applications, we devised atechnique for obtaining satisfactory calculateddensity, viscosity, and interracial tension values.This technique is discussed in the section onMeasurements vs Calculations. We believe that our data, along with previously

published information and information yet to come,will advance the development of satisfactorycorrelations, thus reducing. the need for extensivelaboratory srudies of individual systems.

PRESSURE-COMPOSITION DIAGRAMSOIL ATen mixtures of C02 and Reservoir Oil A were

prepared. These mixtures contained C02 concentra-tions of O, 20, 40, 55, 60, 65, 70, 75, 80, and 90mol percent. At i30 F, pressure traverses weremade with each mixture, These traverses started inthe single-phase regicn at a pressure above thebubble (or dew) points and lowered the pressure indiscrete steps, passing from the single-phase intothe two-phase region. .~t each step, the vapor andliquid volumes were measured. The results aredescribed in Fig. 2A. At 130 J?, the critical pointof the C02 -Reservoir Oil A system (where intensiveproperties of the gas and liquid phases were equal)is 2,570 psia and 60-mol percent C02.OIL BEight mixtures of C02 and Reservoir Oil B also

were prepared and studied in the visual cell at 255F. C02 con~en:rations for these mixtures were O,20, 40, 55, 65, 75, 80, and 85 mol percent. Thepressure was varied from 800 to 6,100 psia, and therelative vapor and liquid volumes measured. Thefesults are given in Fig. 2B. The critical point ofthe C02-Reservoir Oil B system at 255 F is 4,890psia and 74-mol percent C02. The addition of morethan 60-mol percent C02 to both Oils A and B

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.

PuRE

500[

400

201

10[

%

vISUAL ~CELL

P- Zc oJ DIAGRAM

--lAS k_ CHROMATOGRAPHY &LOW TEMP. DISTILLATION LIQUIOCOMPOSITIONS,

tCALCULATION e K vALUESCALCULATION * GAS VISCOSITIES

, .

HIGH PRESSURE- CAPILLARY TUBE _

mLIOUIO

VISCOMETER VISCOSITIES

FIG, 1 EXPERIMENTAL PROCEDURE.

-+

I/

BuBBLE POINT REGION -- +-DEWPOINT REGION+

v I1,0 I

< 1 ! ! 1 { I I J. 20 40 Go 80 100MOLPERCENT C021NRESER.91R OIL A

A SOLl O PHASEPRECIPITATEAT zco2 >m

FIG, 2APRESSURE-COMPOSITION DIAGRAM OF OIL1. AT 130 F.

6C9G

Scm

4aQ

[ 6uBBLE POINT REGION l-- OEW POINT-REGION. .1% ?

/lml p / A SOLl O PHASEL

/ PRECIPITATE25 / AT ZC02 > 55%/

o 0 lo202G 405060 7ososolfmMOL PERCENT C02 IN RESERVOIR OIL B

FIG . 2BPRESSURECOMPOSITIQ~ DIAGRAM OF OILB AT 255 F.FEBRUARY,S9ZS 2s -

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OrirJnal MixtureTanperature, FPressure, peiaPhasePhase, mol fraction

C02c1C2

TotaiBubble point, palaW weight , gm&m+nolDenalty, gin/ccVlacasity, Cp

TABLE 1A OIL A EXPERIMENTAL DATA(WcI Percent G02 5&Mol Percent C021O(M4OI Parcent Reaervolr 011 45-MoI Percent Reservoir 01I

130 130 130 1301,660 2,000 2,270 2,420Qaa g Gaa LJul(J Gas w Ciaa L-oi 100 0.%5 0.7765 ___ m 100Y X6(mol fraction) [mol fraction) K = YIX Y3 X3 /(3 y4 )(4 v x K . .0.0Q268

0.821230,097500.064110.015030.004240.001690.001840. CK11J40.00026o.cocr150.000110,000031.00000

20.320.01582

lnterfaclal tension betwean gas and Ilquld, dynes/an

original MlxturaTamparature, FPresswa, palaphaseph a se, m l f ra ct ionComponent

002clC2C3C4C5C6c,c~C9Cloc1~C12%3+ Total

Bubbla fwlnt, psiaMOl weight, gm/grn-rwlDensity, gticcVlsco a lt y , c9Intarfaolsl terwlon betweengas end IIquid, dynes/cm

0.00010.:1000.10410.11870.07320.04410.02550.05710.04720.02480.02330.02120.01690.1340G1,56087.510.8850.345

2.6420,9370.46590.20530,02610.06630.03220.02200.01C570.0064380.00519o,a21775

0.691590.509250.168290.126140.045940.047100.039390.057460.01791 0.037270.007180.023600.003570.013740.004020.031930.002460.026850.000850.014000.000390.013390,0G021 0.012220.0W13 0.008750.000200.07760.1.00000,004100

2,00039,37 70.550.3858 0.69480.04002 -0.434

1.35s1.4820.9750.6860.4810.3W0.2600.1260.09230.03070.02910.01720.01330.0025s

0.67271 0.53484 0.65@86 0.550000.179940.134530.17204 0.139540.047190.046800.05002 0.046840.04581 0.054390.05181 0.053420.023600.034080.02640 0.032940.011860.020840.01705 0.019850.005820.01217 0.00775 0.011470.007240.027980.01000 0.025700.004330.023340.00608 0.02124O.W1O3 0.01231 0.00104 0.011070.0W28 0.01175 0.0C0227 0.010490.00002 0.01071 0.00G052 0.009640.000040.008530.000019 0.007600.00CK)8 0.C6775 0.0000320.08030GO===

2,270 ?.420- 40.83 63.560.505 0.7205 0.726- 0.04262 0.2020.05s3

8W401 Percent COZ20-MoI Percent Reservoir 01I130 130 1302,020 2,410 2,920

G= Llquld5 G- Liquld5 GSS =5 -y3 X3 U3 y x K y3 X3 .

0.677400.69637 1.280 0.67672 0.63766 1.374 0.87991 0.233660.083@ 0.05517 1.143 0.06358 0.04931 1.269 0.0841C 0.019210.019130.020540.931 0.018050.02152 0.885 0.01904 0.025310.018770.019870.945 0.017770.02661 0.666 0.01601 0.036430.010000.011970.635. 0.00921 0.017860.522 0.00S84 0.036340.C414220.009450.447 0.004280.012160.360 0.003760.031960.002220.008750.254 0.00231 0.01041 0.222 0.00182 0.03C67

C,+ 0.005200.177690.0292 0.007120.224430.0317 0.004500.58736

K33.7653.3370.7520,5060.2430,1180.0593O,oo?&

@SS Inequlllbrlumwith reservoir oi l at btbble F9int.%3SSvi~oeitlea were calculated.3Anal yz@ ~ . a a ea ,eatlnrsted K valuea, calculated liquidcwnpzsitions, rreaawad denalties and lFTa.

. . .I.oww 1,00000 1.00000 1.00000 1.00000 1.000002,020 2,410 2,920

42.69 85.62 42.82 97.41 42.58 187.280.476 0.821 0.512 0.830 0.561 0.8480.04622 0.05682 o.Ce302 1.097 0.919 0.775

22

1.1921.2331.~60.9660.s620.8590.6760.3890.2880.09390.02160.W8450.002500.0005s1

4Eat[@ed K val uea, calculated gaa and IIquld@3MpOWthIIS,measureddensltles and IFT.sContains black aolld Pradpitate.

6_7hia la ;he composition of 011A.

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caused black solid particles to precipitate. Theamount increased to about 80-mol percent C02, atwhich point the precipitate was about 2 volumepercent of the original reservoir oil. The propertiesof the precipitate were not measured.

GAS AND LIQUID COMPOSITIONSOIL A

S ix tw o-pha se mixtures w ere prepa red in thevisual cell at the following conditions.

Mol PercentMix C02 in System Psia at !30 F-i- 0 1,66Q2 55 2,000

55 2,420: 80 2,020

80 2,410: 80 2,920The gas phase for each mixture was analyzer! by

chromatography. For Mixtures 1, 3, and 5, the liquidphase was dehexanized in a low-temperature,fractional-distillation column. Composition of thec, - C6 cut from the liquid was determinedchromatographic ally, and the molecular weight anddensity of the C7+ cut measured by cryoscopic andgravimetric methods, respectively. The C7 + cutwas analyzed further by obtaining a true boiling-point (TBP) curve and subdividing it into normalparaffin components from ~ through C12 and aresidual C13 + fraction.

1/C ,*t~.,1-3 -2 -1 0 1 2 3 ~

F. b(l/TB - l/Tl

FIG . 3 KP VS F PLOT OF OIL A AT 130 F.

t %1I,2qI 1 I 1 I I 4-3 t -1 0 1 1 3 4F . b ll iTB - 1/?1

FIG , 4 KP VS F P LOT OF A MIXTURE OF 55-MOLPERCENT CO, AND 4S-MOL PERCENT G IL A AT.., 130 F.

1~, f= (lrr~ - mlFIG . 5 KP VS F P LOT OF A MIXTURE OF 80-MOLP ERCENT CO ~ AND 20-MOL PERCENT OIL A AT

130 F .FEBRUARY,1978 23

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Original MtxtureMix No.Temperature, Fpressure, psiaPlrasePhase, mol fractionCcmponwrt

cotc1C2CJC4C5r26%%%c,~c,,c,?C,3c,~c,~CJ6c,,+

TotalBubble point, psla

TABLE IB OIL 0 EXPERIMENTAL DATA4*I Percent C02 5&M01 percent C02 6H#Jl Percent C0255-MoI Percent 42-MoI Percent 35-MIX PercentOil Bl 75Mc4 Percent C02Reservoir Oil Reservoir Cil Reservoir Oil 25-W Percent Reservoir 011 15-J!%%&c%%%lr.- 1 . 2 3 4 5255 255 255 255 255 255 2552s54 3,023 3,970 4,020 3,020 4,0Lb9 4,rx?o

ad La LJ&d ~ ~d Qa& ~d *S Licuid * ~d Gas &d Gss1.00 0.679 0.321 0.550 0.450

Y {M131 x (mol Mol Ml!@!9!U!@!Q!l _!!___ . raction Fraction Y x K Y x K Y x h Y x K Y

0.01380.3870O.(M310SW50.02950.02820.0271~+ 0.4239

-l.orm2,554

0.578570.333740.027020.014410.009470.006500.005600.00699o@39020.003460.001990.000760.000290.0001o0.00003O.olx)ol0.000o1O.otmol1.00000

o.3K160 3.4810. 185% 1 .7950.02355 1.1470.01770 0.81410.01605 0.59000.02105 0.40380.01678 0.32370.02300 0.24860.04685 0.19250.02072 0.16700.01772 0.11230.01700 0.04520.01640 0.01770.01552 0.00640.01545 0.00190.01508 o.rmo70.01294 0.00080.12263 0.0001l.cK)ooo3.028

Mot weight, gtigrmnrol 120.3 36. % 100.6Oensily, gtiec 0.643 Viscosity, cp Interracial tension between gae adliquid. dyneahn

0.3EI0 0.6750.039 0.219

0.451

0.72930 0.55456 1.3150.18704 0.12363 1.5100.01723 0.01477 1.1670.01101. 0.01098 1.0020.00853 0.01163 0.80560.00775 0.01300 0.5%20.00634 0.01204 0.52660.00856 0.01811 0.47270.01184 0.02(B6 0.57300.00516 0.01320 0.39090.00344 0.01313 0.26200.00155 0.01307 0.1166o.o@69 0.01303 0.05300.00029 0.00387 0.03270.00012 0.01589 0.02760.00007 0.01127 0.00620.00003 Q. O1O32 0.00290.00005 0.12143 0.0002 1 . Oo rx )o 1.00000

4,02041.59 89.73

0 .84445 0.50572 1.6700 .11052 0.06628 1.6670 .01052 0.01315 0 .8000 .00628 0.01170 0 .53630 .00533 0.01326 0 .40200.00420 0.0?286 0.32360 .00329 0.01332 0.24700 .00417 0.02110 0 .19210 .00556 0.03333 0.16680 .00223 0.01653 0 .12030 .00164 0.01843 0.08800 .00094 0.01635 0 .05120 .00051 0.01322 0.02790.00023 0.01245 0 .01850.00008 0.02231 0.011360.00003 0.01532 0 .00190 .000V 0.01443 o.c@7O.00001 0. :?050 0.00006 1.000oa l.m~

3,02042.30 117.310.351 0.714

0.847170.104450.010130.003300.CW550.004570.00379O.wiol0.006480.002400.001520.CQ0720.000490.000370.000330.000300.00021o.oott211.00000

42.870.400

0 .63178 1.342 0.919020.09017 1.158 0.054S0.01226 0.8263 0.W5360.C0920 0.6848 0.003420.00360 0.6307 0.003170.00857 0.5333 0.002710.00383 0.4244 0.00243o.o133a 0.3744 0.002970.02078 0.3118 0.002910.01179 0.2036 0.001420.01173 0.1296 0.00087o.txW32 0.0773 0.000460.01007 0.0467 0.000280.01185 0.0312 0.000160.01420 0.0232 o.lMro90.01500 0.0200 0.000080.00922 0.0228 0.000050 .10355 0.0020 0AW04I.oormo 1.lKtooo4,008q 85.80 43.360.702

lAISO ccrrtained 0.0027 molfraction N2; NOTE: Liquids frommixtrrrea contahring >55 mol percent C02 had black solid pn%:pitate.~gg~:ee~:jl ~;epq st60 F = O.&AP I = 35.25.

0.66999 1.372 0.918170.04457 1.224 0.056550.00616 0.8701 0.W5600.~513 0.6667 0.003550.00577 0.54~ 0. C93200.%

0 .4274 0.002630. 55 0.4378 0.oo2230.02827 0.1051 o. oo%O0.01012 0.2875 0 .oo2420 .01307 0.1086 0.001180.01300 0 .0869 0.000820 .01Z95 0.0355 0.000420.01280 0 .0217 0.000320 .IX1378 0.0182 0.000270 .01574 0 .0438 0.000100.01116 0.0072 0.00(K140.01022 0 .0049 0 .000030.12028 0 .0002 0.00002.1.00000 1.000004@2099.68 43.20

.

.--....

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Equilibrium vaporization constant values [Ki = y~(mol fraction, compound i in vapor)/xi (mol fraction,compound s in liquid)] were calculated from the gasand liquid compositions of Mixtures 1, 3, and 5.These values are given in Table 1A. These K da tawere used to prepare the KP vs F plots shown inFigs. 3 through 5. This type of plot is used tolocate data inconsistencies and to estimate Ks forcompounds whose vapor and liquid concentrationsare nut measured. Fig. 3 shows, a conventionalstraight-line KP vs F plot for the reservoir oil.12Figs. 4 and 5 show KP vs F values for 55- and80-mol percent C02 systems. Additional data Of thetype in Figs. 4 and 5 are needed to deveiop ageneralized correlation for C02-rich systems.OIL B

The same exper iment a l procedure w a s follow edto obt a in composit ions a nd equilibr ium const a ntvalues at 255 F for the following six C02-ReservoirOil B systems.

Mol PercentMix C02 in System Psia at 130 F1 45 3,0282 (55 4,0203 75 3,0204 75 4,008

85 4,0202 85 5,020

For these mixtures, the C7 + cut from the Iiqukl wasdivided by TBP distillation into C7 through C16components and a C17 + residual. The results aregiven in Table 1B. KP vs F plots for C02-Oil B,similar to Figs. 4 and 5, can be prepared fromthese data.

GAS AND LIQUID DENSITIESOIL ADensities were determined by drawing a measured

volume of gas or liquid from the visual CC1l andweighing the fluid at 1 atm. The results for fivegases and seven liquids are in Table 1A.OIL BThree vapor and liquid sets of densities were

measured for Oil B. These are shown in Table lBfor mixtures with 58- and 75-mol percent C02.The measured densities of the seven liquids and

five gases shown in Table 1A were compared withvalues calculated by the Redlich-Kwong equationof state,3 using the compound properties in Table2, For simplification, the C7+ component was dividedinto three cuts light, medium, and heavy, ratherthan six normal paraffin equivalents C7 to C12 andC13+. Calculated values for the seven liquids hadan average deviation from the experimental valuesof 4.2 percent. The calculated densities of fivegases had an average deviation from experimentalvalues of 11.5 percent. The Redlich-Kwon,g equationpredicts liquid densities more accurately than gasdensities, and we have not resolved this unexpectedresult.

TABLE 2 COMPONENT PROPERTIES USED TO CALCULATEMIXTURE OENSITIES, VISCOSITIES, AND INTERFACIAL TENSIONS

C4mponent=CO* 44.01c, 1s,04C* 30.07c~ 44.o@N-C, 5s.12N-C5 72.14C6 S6.17

C,+ FractlonlLight cut 110.69Mediumcut 164.s4Heavy cul ~0$.19

CriticalTsmp&ure,S7.S-1 15.7s90.32W6.42305.62385.92454.5

CM IcalCritical ~~ Acentr[c3Preeaure, Factor, Par3vjwr4-2S!L(!!?SWJ!L__ Chnatmt1,070 1.51 0.225 7S.?2673.1 1.59 0.03s 77.070s,8 2.37 O.OSS 108617.4 3.20 0.152 150.3550.66 4.09 0.123 189.9489.5 4.98 0.251 231.5440 5.90 0.2S0 271645 370 7.79 o.4m6S2 2s0 10.5? 0.530 5C61,004 18s 20.83 0.710

lPropwties of the thrm C,+ cuts are for normalparaffina with equivalentnwlscular welghte.2pwachr of C02 cdculat@ frompure C02 v~r-llquld dsneltY am inter-faclal tension data.3FrumThe Pfo@r fles of Qaees and L Iquids, Reidet cl., 3rd eti.~Fran Hendbcck ct Natural Qsa Engineering, Katz et al.

GAS AND LIQUID VISCOSITIESOIL AGas viscosities were calculated by the Dean and

Stiel method recommended by -Reid.4 Liquidviscosities were measured in a high-pressurecapillary tube viscometer after transferring theliquid from the visual cell. The results are shownin Table 1A and Fig. 6,OIL BThe result of one liquid viscosity measurement

is shown in Table lB.The experimental liquid viscosities were

compared with values calculated by the Lohrenz-Bray-Clark correlations The results of calculationsfor Reservoir Oil A with no C02 differ&d from themeasurements by > 100 percent. Values calculatedfor 55-snol percent C02 / 45-mol percent ReservoirOil A were in good agreement. The average

.s0 I

i

\\.70 ,\

.eo \\\\.50 \\

I ~ CRITICAL PRE33VISCOSITY.I.4JP0 lSOF

.15lMO m m 4M0PRESSURE,SIAFIG . 6 VISCOS ITY VS PRESSURE OF C02 IN OIL A

MIXTURES AT 130 F.FEBRUARY,1978 3s

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10.0

.

1.0 -

as:0~.*

-20 mol%RESERVOIRILA4

t0! , ,0 .20 .44 .a a 1

sOL IMAC1!OM CO IN RUERVOIR 011A

.!

1~ESERVOIR O IL @ 147 5 PSIAIFT.1 1.52 OYNES4CM \ & BUBBLEmlNTPRESSUREPRESSURE, PSIAFIG . 7 INTERFACIAL TENSIONS OF GAS ANDLIQU ID VS P ESSSURE AT 130 F, OIL A.difference between experimental and calculatedvalues was 4.3 percent.INTERFACIAL TENSIONSInterracial tensions were measured for both

reservoir oil-C02 systems in the high-pressureinterracial tensi~meter after transferring the gasand liquid phases separately from the visual cell.Compositions of the mixtures and results of themeasurement for Oil A are shown in Table 1A andFig. 7. Interracial tension values approached zeroas composition and pressure nealed criticalconditions (60-mol percent, C02, p= = 2,570 psia).One interracial tension point for Oil B is shown

in Table lB.Interracial-tension calculations for the com~osi-

tional simulator used the Weinaug-Katz parachorequation.6 The average deviation betweenexperimental and calculated values was 75 percent.

MEASUREMENTS VS CALCULATIONSComparisons of measl)red .vith calculated

densities, viscosities, and interracial tensionswere described previously. We concluded that thereis a need to develop fundamental methods for C02

FIG. S CALCULATED INTERFACIAL TENSION VSPRESSURE AND C02 CONCENTRATION AT 130 F,OIL A.

systems similar to, but more reliable than, theRedlich-Kwong, Lohrenz-Bray-Clark, and Weinaug-Katz equations.For expedience in handling engineering problems,

we improved the agreement of measured andcalculated values by modifying the parametersshown in Table 2 with a nonlinear regressioncalculation that minimizes the sum of squares ofresidual error functions. This resulted in adjustedor artificial values for critical properties,acentric factors, and parachors, Using theseadjusted quantities, we obtained the followingaverage differences between measured and calcu-lated values: densities 1.8 percent; viscosities 6,3 percent; and interracial tensions (see thosein Fig. 8) 3.6 percent. These are suitable forreservoir engineering and compositional simulatorapplications.

L

2.

3.

4.

5.

6.

REFERENCESHoffma n, A. E ., Crump, J. S., and Hocott, C. R.: