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SPE 029567

Viscosity Behavior of Carbon Dioxide Treated Cut BankCrude OilG. V. Cady*, Montana Tech and Houssain Mosawi*, University ofOklahoma*SPE Members

Copyright 19S5, SOOkfY Of PStmleuM EWinW% ific.

This paper was prepared for presentation at the SPE RockY Mountain RegionaULwParmadtiW Reaamim SymPium heM in Mnver, co, U. S.A., *Z Much 1~5.

T~sp@arwaSadS121~ forpraaa”tatio+lby an SPEPrWramCommfflW followiWravkwof informetionmnttin~ inantirati~bminti bytheatih~s).co~ene Oftheww,aepraaantad,hsve netbeanrav~ bythe%cietyof PatroteumEn9i-re andareaubjatto corraotionbytk aufhof(a).Thematerial ,aapf-nt~,~s @~lYre*any poaitkm of the Sociaiy of Petroleum Engineers, its otfkera, or mambara. Papers praaantad at SPE maetirwa are aublWf to PuMicatbn ravlaw by Edifotial COrnmMWs ~ the SIJOWof patrofaum Enginaara. parmiaaion to copy is raatrictad to an abawaot of not more than SCCIwwds. llluatmfioIw may not W COPM. The tir~ s~~ ~~in ~~us ~k~~g~WSS4SSS, U.S.A. Telex, 1SS245 SPEUT.of tie and by whom the paper is presented. Write Librarian, SPE, P.O. SOX SSSW6 R~hwdwJn, ~ 7

Abstract

Carbon dioxide injection,either by huff and puff ordisplacement operations,results in a crude oilviscosity reduction atpressures below themiscibility conditions” carbondioxide miscibility occurs inreservoirs at miscibletemperature and press-are, blUtthese conditions are notpossible in shallowreservoirs. Improved oilrecovery in a shallowreservoir depends on the

degree of viscosity reductionat the reservoir temperatureand pressure. A recovery

project’s success depends onthe interaction between thecarbon dioxide and thereservoir system.

A research project carried outat ~on~arla ~~~p~~~ study the

viscosity reduction and carbondioxide volubility in Cut Bankcrude oil at the reservoir’sprevailing temperature andnear fracture pressure shows aviscosity reduction ratio(crude-carbon dioxide mixtureto original dead oilviscosity) of 0.22 at apressure of 1000 psig and

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90”F. An original mobility of20 Md/cp improves to 91 Md/cpunder a carbon dioxiderecovery process at or nearthe reservoir’s fracturepressure.

Based on our research,improved oil recoveryoperations in the Cut BankField, Montana, is viable whenusing a commercial on sitecarbon dioxide recovery orgenerating system to minimizethe cost of C02transportation. The majorbenefits ar oil viscosityreduction, mobility ratioimprovement, gas driver andcrude oil swelling.

Introduction

Carbon dioxide injection toenhance oil recovery waspresented by Pirson (1) at theCentral Appalachian SectionAIME meeting on June 26, 1941.Since that time, severalapplications for carbondioxide injection to increaseoil recovery appeared in theliterature (2,3,4,5,6,7,8,9).One application of interestfor shallow low pressure-lowtemperature reservoirs is theimmiscible method presented byChung (5). Bargas et. al.(8)and Scarieret. al. (9) reportedon field tests involvingimmiscible C02 displacement.

Chung (5) observed that C02displacement was influenced by1) viscosity reduction, 2) oilswelling, 3) COL volubility,and hydrocarbon extraction.His study concentrated onheavy oils (10 to 20 API) andthe change in viscosity,

swelling, and density forimmiscible oil-COL mixtures.The report gives a viscositycorrelation for predicting theviscosity reduction caused byC@-oil mixtures. He concludedthat C02 immiscibledisplacement is a potentialheavy oil recovery method. Healso concluded that elevatedpressures extracted high-molecular weight compoundsfrom the oils which improvesthe C02 phase mobility.

Two field test of theimmiscible C02 displacementinvolved the Salt Creek Fieldin Wyoming (8) and theWilmington Field in California(9). Reservoir temperature wason the order of 90 to 120 ‘Fat depths from 1500 feet inWyoming to 2500 feet lilCalifornia. The oil gravitywas 38 ‘API in Wyoming and 14“API in California. Both fieldtest used the WAG process todisplace the C02. Theinjection pressure variedwidely from about 550 to 1000psi. In the Wilmington test,the injection pressure climbedto 1400 psi immediatelyfollowing the water injectionperiods, but decreased rapidlyas gas permeability developed.The conclusion from both fieldtests indicated the viabilityfor immiscible C02 flooding.

Statement of Theorv andDefinitions

The fundamental theory anddefinition for phase behaviorand petroleum systemthermodynamics has beendefined in the literaturesince Muskat (10) published

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his book on the physicalprinciples of oil productionin 1929. The physical andchemical behavior of gas-liquid systems evolved fromconcepts in physical chemistryand physics involvingDalton’s, Amagat’s, andHenry’s laws as well asseveral equations fordescribing the physicalproperties of liquids andgases. These concepts arepresented in severalcorrelations for petroleumcrude oils! gases andcondensates which are toonumerous to review in thispaper. Important to this studywas the “w-cIrk by- siimn ad

Graue (11).

Volubility, swelling, andviscosity for COL-crude oilsystems in general waspresented by Simon and Graue(11) with a review of theearly published data availablefor COZ injection projectdesign. Their work shows thechanges in volubility,swelling and viscosity for 40different CO~-crude oilmixtures at temperatures from110 to 250 “F and pressures upto 2300 psia. However, severalreservoirs which may benefitfrom COZ injection containcrude oils that were nottested by Simon et.al. are atvery low pressure andtemperature compared to rangesdefined above. This workextends the correlation topressures and temperature notcovered by Simon.

Equipment Description andApplication

Four main divisions for theequipment include the RuskaHigh pressure mercury pump, aRuska visual liquid cell andoil bath, a Ruska highpressure/temperature rollingball viscometer, a Ruska flashseparator with a wet testmeter, and all necessarypressure indicating andcontrol equipment. A schematicdiagram showing the betweenthe parts of the apparatus isshown in Figure 4. The partsof the apparatus wereconnected with 1/8” SS tubingand high press-ure fittings.

The mercury pump (Ruska model2251-01055) supplied pressureto the window cell and changedthe volume in the cell. Pumppressure was indicated by aHeise, model 71OB, 10,000 psidigital pressure gauge througha Ruska 45301 diaphram. Themercury pump is operated byhand or with a motor andcontroller set up. Thevolumetric mercury pump has aprecision scale to determinevolume displacements to .001cc .

The high pressure window cellwas mounted in a Ruska 2318oil bath for temperaturecontrol to 1 “F. The insideoil bath diameter was 18inches and the bath holds 18gallons of heating oil. Theoil bath is equipped with anauxiliary oil chamber to allowa Pmp to raise or lower theoil surface in the window cellchamber. The window cell is ahigh pressure vessel with a

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tempered glass window forvisual observation of gas/oiland oil mercury interfaces.The cell operates at pressuresup to 10,000 psi andtemperature to 300 ‘F. Thecell window is 1.75 by 3/16inches and faces the rear ofthe oil bath. Interfaceobservations are made througha mirror mounted to the oilbath to allow viewing withoutlooking directly into thewindow.

The high pressure viscometeris a Ruska Model 1620-820rolling ball viscometer with aseries 230 LFE controller. Theviscometer determines thesample viscosity at thereservoir temperature andpressure. The viscometer hasitis own heating jacket tomaintain the reservoirtemperature during viscositymeasurement. Two levelingscrews and a level vialprovide necessary levelingcapability for the instrument.A solelluLu is Uacu

---4-I 1..-,4 ~~ ~JQ~cj ~~.~

hall ~~ ~h~ ?_op Qf the barrel-u..until the operator is ready tomeasure the viscosity. Thecontroller releases the balland times the ball’s fallthrough the liquid toeliminate timing errors.

A Ruska model 2353-803 flashseparator is used to measurethe gas in solution. Theseparator is a graduated glasscylinder equipped with apressure regulator, pressuregauge, and valves. Theseparator is used todepressure the sample andmeasure the gas and liquiddrawn from the instrument as

the pressure on the sample isreduce to atmosphericpressure. The gas isdischarged to the atmospherethrough a Precision Scientific14AM5 wet test meter. Dead oilafter the gas is separated ismeasured in a graduatecylinder.

Experimental Procedure

The apparatus was cleanedbetween each experiment byflushing the entire systemwith hexane. With the windowcell full of mercury, hexanewas drawn into to cell byremoving the mercury from thecell while a 200 ml graduatecylinder was placed on a filltube at the top of the windowcell. The cell was then

A lJp4~~~~~.~fl-usFledand reflllsuhexane became clear. Followinga similar procedure the linesleading to the viscometer andthe viscometer were cleanedwhiie the soivent was bledfrom the viscorneter’s lower.U.v=. Similar-y the flash172 1 Trn

separator was cleaned withhexane. Following the hexaneflushing the instruments areplaced under a vacuum toremove the solvent wetting theinterior surfaces.

The visual cell was filledwith the oil sample byattaching a 1/8” stainlesssteel U-tube to the top of thecell and inserting the openend to the bottom of agraduate cylinder filled with200 cc of the dead oil.Mercury, which was previouslypositioned at the top of thewindow during the cleaningprocess, was drawn out of the

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Pal 1 1.1+ th ~~~~ ~L~~_1J~}7 ~l&~L~bLA.L VV-LLAA

until the entire 200 cc oilsample was in the visual cell.

Removing the U-tube with thetop cell valve shut, a directline was connected to a C02bottle and a slight positivepressure was applied to injectC02 into the cell. With thecell valve open, a 117 cc C02sample was drawn into thewindow cell at roomtemperature and atmosphericpressure.

The cell’s temperature wasincreased to 90”F using theoil bath and the cell pressurewas increased to experimentalconditions of 200, 400, 600800, and 1000 psi over thecourse of the test using themercury pump. Once theobjective pressure was set,the visual cell was rocked for12 hours to achieveequilibrium between the COZgas phase and the crude oil.Any excess gas phase wasremoved from the cell and theliquid mixture was transferredto the viscosimeter in 10 psiover pressure steps which keptthe experimental pressure inthe cell at or above theobjective test pressure.

The 60 cc sample in theviscometer was allowed toequilibrate for 2 hours at thetest condition set for thevisual cell. The fall time at23° 45”;—-,. &lD.d70” w~~~ taken-=

With the viscometer isolatedfrom the system, the bottomdischarge valve was slowlyopened to the flash separatorand a sample of the test fluid

Lla< flnl laet=cl at 2 n~ca==llw=..W” ““..V”WU w u. u JFJ--=V-”-

equal to the test pressure orat 600 psig (whichever wassmallest) . The separator’spressure was then lowered toatmospheric pressure while thegas was metered through a wettest meter. The remaining deadoil in the separator, aftercomplete pressure depletion,was measured in a graduate—--l2-––3–-.cylmaer.

These experimental steps werefollowed at each objectivepressure set in the visualcell. Occasionally theexperiments were duplicated totest the data’s precision.

Data and Results

Table 1 shows the Cut Bankcrude oil properties for theoil sample from SCCBSU/well21-1 used in these studies.Table 2 gives the fractionalanalysis up to C30+for SCCBSUwell 50-5. The crude is a 30.5‘API, 9.12 cp (100 ‘F) blackoil with a 1.49% sulfurcontent.

Our data for viscosity,swelling, and solution gas aregiven in table 3 at thevarious test conditions. Ingeneral, we found that thecarbon dioxide saturated CutBank crude oil at 90 ‘F and1000 psi has a solutiongas/oil ratio of 429 scf/bbl,a 36.7 ‘API gravity, a 1.1502swelling factor, and amixture-to-dead oil viscosityratio of 0.375. Data trends atthe individual test conditionsare shown in figures 1, 2, 3,and 4.

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Data Interpretation

The viscosity and solution gasbehavior shown in figure 1 forCut Bank crude is normalcompared to other empiricalstudies. A comparison of theviscosity ratio to Simon’s etal (11) work is presented infigure 2. One must bear inmind that Mosawi’s (12) data isbased on 90 “F and 1000 psigfor a 30.5 gravity crude oiland Simon’s data was based on120 “F and 1000 psia for a33.3 gravity refined oil inthis viscosity range. Simon’scrude oil with a similargravity to Cut Bank only had adead oil viscosity of 4.4 cpat 120 “F. Viscositycorrection suggested by Simonaid not account for thedifference between the CutBank Crude and Simon’s’scorrelations.

The swelling factor was 1.1502as reported by Mosawi (12).Using the correlations byNelson (13) to find molecularweight from Saybolt viscosity,the approximate swellingfactor from Simon is 1.18.

Conclusions

Cut Bank Crude oil responds toC02 treatment in a normalmanner as indicated bycorrelations. The empiricaldata indicates that thereservoir conditions of 90 “Fand 1000 psig will yield acrude viscosity of 3.821 cp ascompared to a dead oilviscosity of 17.64. The crudeoil will swell by 15% of theoriginal volume and the COZsolution gas is 429.3 scf/bbl.

Correlation to Simon et. al.(11) is difficult due todifferences in base data.However, the correlationappears to be quite adequatefor preliminary investigationof COZ injection feasibility.We recommend actual PVT teston the oil sample before thefinal pilot or full scaleproject design. Attention isrequired for differences intemperature and saturationpressure, but the definitionof the oil viscosity, gravityand UOP characterizationfactor prove to be moredifficult when using thecorrelations.

Acknowledgment ts

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appreciation to Harry Flook,Ruska Instrument Corp., forhis help on experimentalprocedures, solutions toinstrument problems, and safelaboratory operations.

We also thank John Finstad forhis valuable help in obtainingdata and an oil sample fromthe Cut Bank field.

References

1. Pirson, S. J.:’’TertiaryRecovery of Oil,” Paperpresented before the Cen.Appalachian Sec., AIME,June 26, 1941

2. Welker, J. R. and Dunlop,D. D.:”PhysicalProperties of CarbonatedOils, “ JPT, (Aug 1963),873-874

3. Kokal, S.L. and Sayegh S.

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G ““Phase Behavior and..Physical Properties ofC02 Saturated Heavy Oiland ConstitutiveFractions: Experimentaland Correlations, iiElsevior, Amsterdam,JPSE, 9, 1993, 289-302

4. Helm, L.W. and Josendal,V. A.:”Mechanism of OilDisplacement by CarbonDioxide, ” JPT, (Dec.1974), 1427-38

5. Chung, T. H.:’’Heavy oilRecovery by CO?Immiscible DisplacementMethod,” USA DOE,Bartlesville, Niper-76(DE86000281), Cont. DE-FCOl-83FE60149,Apr. 1986.

6. Johnson, W.E, MacFarlane,R.M., and Breston,J.N. :“Change in PhysicalProperties of BradfordCrude Oil When Contactedwith Dioxide andCarbonated Water,” Prod.Me., (Nov. 1952), 16-22.

7 ~~ff~p+i ~.L. and Yelliq(r.

W.F.:”Effect of MobileWater on Multiple ContactMiscible GasDisplacement, “ SPE/DOEpaper 10687 Presented atthe 3rd Joint SPE/DOESymposium on Enhanced OilRecovery, Tulsa, Apr 4-7,1982.

9. Scarier,W. B. and Patton,J. T.:”C02 Recovery ofHeavy Oil: The WilmingtonField Test,” SPE 12082,presented at the 58thm--..-l Illn-kn.i -.1.atlIludJ- leullll-1-ba~ ~op~f .

and Exhibition, SpE/AIME~San Francisco, CA, Oct.5-8, 1983

10. Muskat, M:PhysicalPrinciples of OilProduction, McGraw-Hill,New York, 1949.

11. Simon, R. and Graue, D.J.:“GeneralizedCorrelations forPredicting Volubility,Swelling and ViscosityBehavior of CO~-Crude OilSystems, ” JPT, (Jan.1965), Pg 102-106

8. Bargas, C.L., Montgomery,H. D., Sharp, D. H., andVoslka, J.L. :’’ImmiscibleCOZ Process for the SaltCreek Field,” SPE Res.Eng., (November 1992), pg397-402

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12. Mosawi, H. H.:’’ViscositYDetermination of COZSaturated Cut Bank Oil,”,Master Thesis, MontanaTech, (July 1994)

13. Nelson, W. L.:PetroleumRefinery Engineering,McGraw-Hill; New York,1958.

.

Table 1- Cut Bank Crude Oil Analysis; well SCCBSU21 -I

API gravity @ 60 OF.................................................................... 30.SSpecific Gravity 60/60°F .............................................................. 0.874Sulfur, % by weight ...................................................................... 1.49Pour Point, “F.............................................................................. -15.Color ........................................................................................... Black

alnAOPL IA CT TCOl q.-‘v’iscosity:w 1uu r U1.u aud, 7.1A Cp

@120 “F 52.7 SUS, 6.98 CP

Hemple distillation @ 26.5 in Hgnl- L.. XTAl.. _-70 Uy v Ululllc C-*A4G* P–w..; +.,OpcLlllu Ulcl v lcy

Gasoline @?392 “F 25.5 0.718I Kerosene @ 500 ‘F 11.6 0.802

Reduced Crude 59.8 0.955Loss 3.1 ..........

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Table 2- Cut Bank Crude Oil Composition; well SCCBSU 5

Carbon Numberc 1-C5

C6C7~~

C9CloCllC12C13C14C15C16C17C18C19C20C21C22C23C24C25C26C27C28C29

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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C30+ ......................................................................

O\OHC by volume8.2006.2005.900

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Table 3- Cut Bank Crude Oil and Caibon Dioxide Mixture Properties

Pressure Viscosity Viscosity Solution Swelling Gas-OilReduction gas factor Ratio

PSIG centipoise POj Pm scfhbl scfhbl

14.7 17.64 ---------- ---------- ---------- ----------

200 15.35 0.87 11.1 1.0039 9.9

400 11 0.62 71.6 1.0251 15.9

600 8.65 0.49 142.8 1.0501 25.3.A -Wu 6.75 0.38 286.2 I.iwz 45.4

1000 3.821 0.22 429.3 1.1502 47.7

252

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0 200 400 600Pressure, psig

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400

300

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Figure 1- Cut Bank Crude and Carbon DioxideMixture Properties

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0 200 400 600 8001000Pressure, psia

,Figure 2- Viscosity Ratio for C02/Crudemixtures at 120 and 90 F :

253

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Pressure, psig3- Cut Bank Crude Oil Swelling Factor whenFigure

saturated with carbon dioxide.

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Figure 4 - Schematic diagram showing the experimental apparatus