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An experimental investigation of wettability alteration during CO2 immiscible flooding
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An experimental Investigation of wettability alteration during CO2 immiscible flooding Saad M. Al-Mutairi, Sidqi A. Abu-Khamsin, Taha M. Okasha, Saudi Aramco, M. Enamul Hossain
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PII: DOI: Reference:
S0920-4105(14)00125-9 http://dx.doi.org/10.1016/j.petrol.2014.05.008 PETROL2657
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Journal of Petroleum Science and Engineering
Received date: 6 June 2012 Revised date: 28 April 2014 Accepted date: 17 May 2014 Cite this article as: Saad M. Al-Mutairi, Sidqi A. Abu-Khamsin, Taha M. Okasha, Saudi Aramco, M. Enamul Hossain, An experimental Investigation of wettability alteration during CO2 immiscible flooding, Journal of Petroleum Science and Engineering, http://dx.doi.org/10.1016/j.petrol.2014.05.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
An Experimental Investigation of Wettability Alteration during CO2 Immiscible Flooding Saad M. Al-Mutairi, KFUPM, Sidqi A. Abu-Khamsin, KFUPM, Taha M. Okasha, Saudi Aramco and M. Enamul Hossain*, KFUPM Abstract Wettability has been recognized as one of the key parameters controlling the remaining oilin-place. The knowledge of reservoir wettability is essential to understand the fluid displacement mechanisms, and to develop strategies for achieving higher recovery factors. One of the effective approaches to enhance oil recovery significantly is wettability alteration which has been investigated extensively in the literature. This paper investigates wettability alteration experimentally, on continuous basis, during CO2 immiscible flooding. Measurements of the contact angle between oil, carbonated brine and a slice of rock cut from a carbonate core plug were conducted. The results indicate that the rock wettability is altered from oil-wet to intermediate-wet when the oil/rock system is exposed to dissolved CO2. The extent of wettability alteration is controlled by CO2 exposure time; as such time is increased, alteration of wettability progresses towards an apparent limit. It is also found that as the CO2 concentration increases in the brine, wettability alteration increases. Based on the experimental finding, an empirical model is developed to describe such continuous wettability alteration. The findings of this study can be applied to the cases where CO2 is injected in a watered out, oil-wet reservoir at a pressure below the miscibility pressure. Keyword: oil-wet reservoir, exposure time, contact angle, reservoir modeling, enhanced oil recovery Introduction Wettability alteration is an effective approach to enhance oil recovery significantly. Buckley et al., (1998) summarized four main factors affecting wettability alteration which are: oil composition, brine chemistry, rock surface mineralogy and the system temperature, pressure and saturation history. The adsorption and the deposition of organic polar components in the crude oil can alter most of the rock surface chemistry. Brine salinity and pH strongly affect the charge of the rock surface where the rock surface becomes positively charged when the pH is decreased and the rock surface becomes negatively charged when the pH is increased. The solubility of wettability-altering compounds tends to increase when temperature and pressure are elevated. Wettability alteration during CO2 flooding has been investigated extensively in the literature through core experiments (Stalkup, 1970; Tiffin and Yellig, 1983; Maini et al., 1986; Potter, 1987; Lin and Huang, 1990; Rao et al., 1992; Vives et al., 1999; Zekri et al., 2007; Fjelde and Asen, 2010). Investigators have proved experimentally that the wettability can be altered because of CO2 injection. Also, the laboratory experiments showed that the interfacial tension reduction may contribute to wettability alteration (Chalbaud et al., 2006; Shariat et al., 2012). On the other hand, a limited number of modeling studies on wettability alteration during CO2 displacement is documented in the literature (Tehrani et al., 2001; van Dijke and Sorbie, 2002; Farhadinia and Delshad, 2010; Ju et al., 2010; Kalaei et al., 2012; Mutairi et al., 2012). Most of the documented experiments or modeling works conducted on wettability alteration were devoted to CO2 miscible displacement where a super-critical CO2 phase comes into 1
*Corresponding authors: Dr. M. Enamul Hossain, Department of Petroleum Engineering, College of Engineering Science, King Fahd University of Petroleum & Minerals, Dhahran 31261, KFUPM Box: 2020, Saudi Arabia. Tel: 0096638602305 (O), Fax: 0096638604447. Email: [email protected], [email protected]
contact with w the reservoir fluidss. Work on displacemen nt by CO2 uunder low pressures p in a watered out reservoiir has not been b reporteed. This papper reports tthe results of o a study on o wettabilitty alterationn on a conntinuous bassis under suuch conditioons. The stuudy involveed experimeents to meassure the oil/bbrine contactt angle on a core slice ccut from a carbonate corre in the preesence of CO O2. The conttact angle waas measured at different times until equilibrium e is attained. The results were used to t develop a simple moddel that preddicts wettabiility alteratioon with timee. ment of Moodel on Wetttability Alteeration Developm Core flooding experriments showed that thhe maximum m oil recoveery apparen ntly occurs in i ( annd Mungan, 1971; Lorennz et al., 19774). Strong oil o neutral or slightly oill-wet cores (Morrow pies the smaall wettabilitty results inn low oil reecovery becaause the weetting phase (oil) occup pores, whhich leads to o a high resiidual oil satuurations. In contrast, c thee residual oill saturation in i intermed diate-wet rocks decreasses if wateer shares thhose small pores. Theerefore, it is theoreticaally plausiblle to speculaate that the rresidual oil saturation w will follow an exponential relationshhip with the rock wettabbility as depicted in Fig. 1.
Figu ure 1: Residu ual oil saturaation variatioon with conttact angle w an oil-w wet porous medium fullly saturated with water at residual oil o saturationn; Starting with and if wee expose thee system to CO C 2 gas, the wettability is expected to graduallyy change from m oil-wet to intermediaate-wet as CO C 2 diffusess through thhe water andd oil to the rock surfacce. c ons, the rate of o Since forr a given sysstem diffusioon is controllled by the diifference in concentratio diffusionn would declline exponenntially with ttime as such difference ddiminishes (Grogan et all., 1986). As A the channge in contaact angle iss directly reelated to thhe concentraation of CO O2 moleculees at the oil//rock surfacee, and as the rate of buuild- up of such concenttration is alsso diminishiing exponenntially with time, the coontact angle would thenn be expecteed to decreasse exponenttially with CO C 2 exposurre time as conceptually c y depicted inn Fig. 2. However, H succh decrease would apprroach a certaain new anggle asymptottically as thee contact anggle cannot go g below zeero.
2
Figgure 2: Conttact angle vaariation with CO2 exposuure time c the relationshipps between wettability w annd CO2 expo osure time caan Based onn the above concept, be modelled as follow ws:
θ = ae−bt + c
(1)
Where θ : Contaact angle
t : CO2 exxposure timee a, b and c : Constantss related to roock and fluidd compositioons as well aas aging history and process parameters. p Inspectioon of Eq. 1 reeveals that c is the ultim mate contact angle a ( θmin ) reached at in nfinite exposuree time ( i.e. t → ∞ ) . The constant c a theen becomes the difference between the t initial contact angle a ( θi ) annd θmin . The constant b iss related to the t time wheen the contacct angle is practicallly equal to θmin . Such tim me shall be ccalled stabiliization time ( tsb ) and, thhus, b can bee defined as a b = ξ / tsb where ξ is a constant w whose signifiicance shall become b eviddent shortly.
d ss form as: Employinng all the abbove parametters, Eq. 1 caan then be reewritten in dimensionles
θ − θ min θi − θ min −ξ t / t = e θ min θ min
(22)
sb
3
Defining dimensionleess contact angle a as θ D =
θ −θ min t an nd dimensionnless time ass t D = , Eqq. θ min tsb
2 becomees:
θ D = θ Di e−ξ t
(3)
D
Where
θ Di =
θ i −θ min θ min
All consttants in Eq. 2 can be estiimated experrimentally ass is presented below. Experim mental Set-up The expeerimental sett-up consistss of eight coomponents as a shown in Fig. 3. A CO O2 cylinder is connected to a 60-ccc visual celll through a regulator to control CO O2 injection. The pressurre perature of the t visual ceell are contrrolled and monitored m thrroughout thee experimennt. and temp The visual cell is maade of stainless steel andd can withsttand high preessures and temperaturees. h is screewed to the roof of the cell c on the innside to whicch a rock sliice is attacheed A steel hanger (Fig. 4). The visual cell c is fitted with w a glass window to allow a monitooring the low wer surface of o mera is placeed horizontaally to the leevel of the visual v cell too allow takinng the rock slice. A cam wnloads the pphotographs to a personnal photograaphs of the contents of thhe cell. The camera dow computerr where theyy are analyzzed by speccial softwaree to estimatte the contacct angle. Thhe Drop Imaage softwaree is providedd by the mannufacturer off the pendentt drop IFT sy ystem.
Figure 3: Diagram oof the experim mental set-up up
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Figu ure 4: Core slice-hanger assembly a
mental Proceedure Experim The carbbonate core plug p was cleeaned and drried in an ovven at 90 °C. The plug was w then fullly saturatedd with brine using u the vaacuum methood followed by floodingg the plug wiith dead oil in i a core-floooding setupp until no brrine is produuced. The pllug’s porositty, pore voluume and final oil and water w saturatiions were thhen computedd by mass balance on oiil and water. Properties of o the rock and a fluids em mployed in the t experimeent are preseented in Tablles 1 and 2. Table-1: Properties of o the rock annd fluids em mployed in thhe experimennt Properrty Oill density (g/ccc) Oill viscosity (ccP) Briine density (g/cc) Briine viscosityy (cP) Corre permeabillity (mD) Corre porosity ((%)
Value 0.85 0.71 0.99 0.56 5 15
Table-2: Brrine composiition Salt Sodium m Chloride (NaCl) Calciuum Chloride (CaCl2.2H2O) Magnesium Chlorride (MgCl2..6H2O)
Concentrration g/L 166.7 3..62 1..28
0 cm thick k, 2.3 cm in diameter d waas immediateely cut from the core pluug A thin coore slice of 0.5 after the dead oil dissplacement. The slice was w then subm merged in thhe same oil and aged in a 8 oC and 20 000 psig for two weeks to t ensure oil wettability y. After agingg, titanium cylinder at 85 o the surfacce of the corre slice was grinded to a uniform plaane to allow accurate meeasurement of the contaact angle. The T polishedd core slice was then ag ged in the ssame oil unnder the sam me conditionns to ensuree oil wettabiility. The coore slice waas then attacched to the hanger usinng special eppoxy cemen nt which has high resistaance to temperature (Fig. 4). The han nger was theen 5
mounted inside the visual v cell. The T cell wass then filled completely with brine and heated to t d oil was thhen introduceed to the ceell 70 ºC annd pressurizeed to 500 psig. A drop of the dead through a vertical neeedle fitted to t the bottom m of the celll. The needlle was positiioned directlly below the core slice so that wheen the drop eenters the ceell it rises thhrough the brine and ressts wer surface of the core slice s (Fig. 5)). The contacct angle betw ween the rocck surface, thhe on the low oil drop and a the surroounding brinne was then m measured.
Fig gure 5: Visuual cell compponents 20 ppm) waas then rapid dly charged to t CO2 gas (99.5% puree with moisture contentt less than 12 mined level (about 1000 psig); CO O2 the cell until the ceell’s pressurre rose to a pre-determ opped. When the cell’s ppressure droopped back too 500 psig, which w usuallly injection was then sto nds, indicatinng complete dissolution of CO2 in tthe brine, hiigh-resolutioon took about 15 secon o drop werre then takeen periodicallly until no noticeable change c in thhe photograaphs of the oil shape off the drop was w observed. The phottographs weere then anaalyzed and values v of thhe contact angle a versus the drop’s exposure e tim me to the carb bonated brine were recorrded. Figure 6 depicts how h the shappe of the oil drop d changed with time. gle using thhe pendent drop methhod is a pu ure numerical Calculatiion of the contact ang techniquee. The cameera’s view fiinder shows a horizontaal line on the screen alo ong which thhe solid surfface is alignned. The filteer routine thhen gives a properly p aliggned drop profile and thhe contact angle a is easilly calculatedd by numeriical derivatioon of the proofile at the contact c poinnt. Because of reflection n in the substrate and soome diffracttion, 2 to 3 data points closest to thhe p are negglected. In th he Drop Imaage software the drop profile p is esttablished by a contact point travellingg secant method with liinear extrapoolation to thhe contact ppoint. This method m seem ms more rob bust than the ones that have been tried out. Itt gives valuees between a pure lineaar derivation, which unnderestimates the contacct angle, and d higher ordder (polynom mial) methodds o the angle. that usuaally tend to overestimate
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Figure 6: Shape of the oil drop (a) before CO2 injection (b) after 44 minutes of CO2 exposure Results and Discussion Two runs were conducted at two different brine CO2 concentrations (0.0004 mole percent for Run # 1 and 0.0008 mole percent for Run # 2). The CO2 concentration was calculated by volumetric balance on the cell’s contents. Table 3 lists the data of both runs, which are also plotted in Figure 7. Since the CO2 was completely dissolved in the brine as indicated by the rapid drop in the cell’s pressure after charging it with CO2, the results demonstrate that the rock wettability in both runs was altered when the rock was exposed to carbonated brine. Wettability alteration is believed to be caused by diffusion of CO2 from the brine into the oil droplet. Once CO2 molecules reach the rock surface contacted by the oil droplet, these molecules start replacing hydrocarbon molecules - mostly asphaltenes – that are adsorbed on the surface and initially causing it to be oil wet. This gradual replacement causes the rock surface to shift its wettability towards water. Diffusion of CO2 from the brine to the rock surface that is covered by the oil droplet involving any route other than through the oil droplet is not realistic because it would involve diffusion through the oil-saturated rock matrix, which is an extremely slow process. In Run # 1, the contact angle decreased from 101º initially to reach a stable value of about 83.9º after 44 minutes of exposure to the carbonated brine. The change in contact angle shows that the wettability of the core slice was altered from slightly oil-wet to intermediatewet. In Run # 2, the stable value appeared to be 69.3 º and was attained in 52 minutes. When the exposure time was extended to 89 minutes in this run, no change was observed in the angle confirming the existence of a stable value in the contact angle. The trend in both data sets reveals an asymptotic-exponential relationship between the contact angle and exposure time. The initial decrease in the angle was rapid followed by a gentle trend towards a stable value. Table 3: Variation of the contact angle with time
CO2 Exposure Time 0 6 8 16 21 23 28 34 40 43 44
Run#1 Conact Angle (degree) 101 90.8 89.4 90.8 88.3 86.4 86.5 86.3 86.8 85.9 83.9
Run#2 CO2 Exposure Time (min.) Conact Angle (degree) 0 97.5 9 96.7 11 95.2 17 74.8 23 72.8 25 72.8 28 73 32 73 34 69.2 36 69.1 39 69.4 44 69.4 52 69.3 76 69.3 83 69.3 89 69.3
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Figure 7: Plot showin ng raw experrimental dataa for Run # 1 and Run # 2 The relattively short time t (less thhan one hourr) it took to complete thhe wettabilityy alteration as a observedd in the twoo runs is neggligible in terms t of thee time scale of field appplications. In I flooding projects whhere the CO2 flood frontt advances at a a speed of o feet per daay wettabilitty alterationn is expected to appear almost insttantaneouslyy. However, in watered--out reservooir rock wheere oil existss as dropletss trapped in small poress with limiteed access by y the reservooir brine, CO O2 gas needss to diffuse through t the water phasee then the oill droplets beefore reachinng the rock surface. At low CO2 cooncentrations, this diffussion processs might takee considerablly me to compllete, causing much sloweer wettabilityy alteration. longer tim d on the CO2 conncentration of o The dataa of Figure 7 also revealls that the sttable value depends the brinee in contact with the oiil with a higgher concen ntration caussing a largeer drop in thhe contact angle. a Howeever, the ex xposure timee needed to reach a staable angle appears a to be b slightly dependent d up pon CO2 con ncentration. One can theen speculate that under the t conditionns of this experiment, where w oil iss surroundedd by brine, diffusion off CO2 into the t oil is faast w concentrattions. It rem mains to bee seen wheether at higgh enough even at rellatively low b altered too a water-w wet state. Taable 4 summ marizes Eq. 2 concentraations the rock could be parameteers as extractted from the data. Table 4: 4 Initial and minimum contact anglees with stabillization timee Ru un Noo.
C 2 CO Conceentration (moole %)
1 2
0.0 0004 0.0 0008
θi
θmin
tsb
(Degrees) 101.0 97.0
(Degrees) 83.9 69.3
(Minutes) 44 52
8
Based onn the parameeter values listed in Tablee 4, θ D was computed aand plotted vs. v t D for botth runs (Fig g. 8). All dataa points fall within one band b indicatting a commoon value of ξ for both runs. Takking log e off both sides of o Eq. 3 yieldds:
loog e θ D = log e θ Di − ξ tD
(4))
T four Re-plotting Fig. 8 wiith semi-log axes (Fig. 9) shows a reeasonably linnear trend. The outlying data points are a attributedd to experim mental error; however, thhe bulk of thee data does fall on thhe same trend d. Excluding g those four data points, the slope off this line is 1.39 1 which is the valuee of ξ for the conditionss of this expeeriment.
Differenttiating Eq. 3 with respecct to tD yieldds: dθ D = −θ Diξ e −ξ tD dt dD
or
dθ D = −ξθ D dt dD
(5))
Equationn 5 shows thaat ξ controls the rate off decline of th he dimensionnless contacct angle withh dimensioonless time. We W can specculate that thhis parameterr is similar for f all other concentraations of CO O2, which maakes predictiing other min nimum contact angles poossible for the rock/oil system of o this study.
9
Figgure 8: Plot showing dim mensionless experimentaal data for Run R # 1 and Run R #2
Figure 9: 9 Dimensioonless experiimental data on semi-logg scale with ffitting curvee for Run # 1 and Run # 2
Conclusiions t study caan be relatedd to cases wh here CO2 is injected in a watered ouut, The significance of this oil-wet reeservoir at a pressure beelow the misscibility presssure. CO2 diiffusion throough the brinne can alterr the rock wettabilityy and rendeer the residdual oil m mobile. In miscible m CO O2 displacem ment processses, such pheenomenon can still occu ur when CO2 fingers advance ahead of o the CO2 slug s and conntact residuaal oil under im mmiscible conditions. c Itt is worth meentioning that more con ntact angle measuremennt experimennts need to be conductted to establlish a generral wettabilitty alteration model – Eqq. (1) – fittedd for differennt rock/fluid systems. Conclusions from thiis study can be summarized as follow ws: C 2 causes alteration of the rocck 1. Exposing carboonate rock to brine ccontaining CO m an oil-wet to t an intermeediate-wet sttate. wetttability from 2. Incrreasing CO2 concentratio on in the brinne results in larger alteraation of wetttability. 3. The oil-brine-roock contact angle a decreaases to a new w stable valuue after a reelatively shoort od of time. perio The channge in contacct angle can be possibly modeled by an exponenntial function n of time where a simple s dimensionless rellationship is controlled by b a parametter, ξ , comm mon to all CO2 conccentrations. 4. The significancee of this expperiment cann be related d to cases whhere CO2 is injected in a he miscibilityy pressure. wateered out, oil--wet reservooir at a pressuure below th Referencces 10
1. Buckley J.S., Liu Y and Monsterleet S: “Mechanisms of Wetting Alteration by Crude Oils,” paper SPE 37230, SPE Journal 3, no. 1 (March 1998): 54–61. 2. Chalbaud, C., Robin, M. and Egermann, P., “Interfacial Tension Data and Correlations of Brine/CO2 System Under Reservoir Conditions”, SPE 102918, presented at the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 24-27 September. 3. Farhadinia, M. and Delshad M., 2010. Modeling and Assessment of Wettability Alteration Processes in Fractured Carbonates using Dual Porosity and Discrete Fracture Approaches, paper SPE 129749, presented at the 2010 SPE Improved Oil Recovery Symposium, Tulsa, Oklahoma, USA, April 24-28. 4. Fjelde, Ingebret and Asen, Siv Marie, 2010. Wettability Alteration during Water Flooding and Carbon Dioxide Flooding of Reservoir Chalk Rocks. paper SPE 130992, presented at SPE EUROPEC/EAGE Annual Conference and Exhibition, Barcelona, Spain, June 1417. 5. Grogan, A. T., Pinczewski, W. V., Ruskhauff, G. J., and Orr, F. M. Jr., “Diffusion of Carbon Dioxide at Reservoir Conditions: Models and Measurements”, paper SPE/DOE 14897 presented at the 1986 SPE/DOE Fifth Symposium on Enhanced Oil Recovery, Tulsa OK April 1986). 6. Lin, Eugene and Huang, Edward, 1990. The Effect of Rock Wettability on Water Blocking during Miscible Displacement. SPE Reservoir Engineering, May. 7. Lorenz, P. B. Donaldson, E.C. and Thomas, R.D., “Use of Centrifugal Measurements of Wettability to Predict Oil Recovery,” report 7873, USBM, Bartlesville Energy Technology Center (1974). 8. Kalaei, Hosein, Green, Don and Willhite, Paul, “A New Dynamic Wettability Alteration Model for Oil-Wet Cores During Surfactant Solution Imbibition,” paper SPE 153329 presented at the 2012 SPE Improved Oil Recovery Symposium, Tulsa, Oklahoma, USA, April 14-18. 9. Maini, B., Ionescu, E. and Batycky, J. 1986. Miscible Displacement of Residual Oil – Effect of Wettability on Dispersion in Porous Media. JCPT, May-June, Montreal. 10. Morrow, N. R. and Mungan, N., “Wettability and Capillarity in Porous Media.” Report RR-7, Petroleum Recovery Research Inst., Calgary (Jan. 1971) 11. Mutairi, S. M., Abu-Khamsin, S. A. and Enamul Hossain, M., “A Novel Approach to Handle Continuous Wettability Alteration during Immiscible CO2 Flooding Process”, paper SPE 160638 presented the Abu Dhabi International Petroleum Exhibition & Conference held in Abu Dhabi, UAE, 11–14 November 2012. 12. Potter G. F., 1987. The effects of CO2 Flooding on Wettability of West Texas Dolomitic Formations. paper SPE 16716, presented at the Annual Technical Conference and Exhibition, Dallas, TX, September 27-30. 13. Shariat, A., Moore, R., Mehta, S., Van Fraassen, K., Newsham, K. and Rushing, J., “Laboratory Measurements of CO2-H2O Interfacial Tension at HP/HT Conditions: Implactions for CO2 Sequestration in Deep Aquifers”, paper CMTC 150010, presented at the Carbon Management Technology Conference, Orlando, USA, 7-9 February 2012. 14. Stalkup, F.I., 1970. Displacement of Oil by Solvent at High Water Saturation. SPEJ (December) 337. 15. Rao, Dandina, Girard, M. and Sayegh, S., 1992. The Influence of Reservoir wettability on Waterflood and Miscible Flood Performance. JCPT, June, Volume 31, No. 6. 16. Tehrani, D., Danesh, A., Sohrabi, M. and Henderson, G., 2001. Improved Oil Recovery from Oil-Wet and Mixed-Wet Reservoirs by Gas Flooding, Alternately with Water. Presented to IEA Annual Workshop & Symposium, Vienna, September.
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17. Tiffin, D. L. and Yellig, W. F., 1983. Effects of Mobile Water on Multiple-Contact Miscible Gas Displacement. SPEJ (June) 447. 18. van Dijke, M.I.J. and K.S. Sorbie, 2002. Pore-Scale Network Model for Three-Phase Flow in Mixed-Wet Porous Media. Physical Review E, 66(4), pp 046302. 19. Vives, M., Chang, Y., Mohanty, K., 1999. Effect of Wettability on Adverse-Mobility Immiscible Floods,” SPE Journal, September. 20. Zekri, A., Shedid, S. and Almehaideb, R., 2007. Possible Alteration of Tight Limestone Rocks Properties and the Effect of Water Shielding on the Performance of Supercritical CO2 Flooding for Carbonate Formation. paper SPE 104630, presented at the SPE Middle East Oil & Gas Show and Conference, Bahrain, March 11-147.
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Lists of Tables Table-1: Properties of the rock and fluids employed in the experiment Property Oil density (g/cc) Oil viscosity (cP) Brine density (g/cc) Brine viscosity (cP) Core permeability (mD) Core porosity (%)
13
Value 0.85 0.71 0.99 0.56 5 15
Table-2: Brine composition Salt Sodium Chloride (NaCl) Calcium Chloride (CaCl2.2H2O) Magnesium Chloride (MgCl2.6H2O)
Concentration g/L 16.7 3.62 1.28
Table 3: Variation of the contact angle with time
14
CO2 Exposure Time 0 6 8 16 21 23 28 34 40 43 44
Run#1 Conact Angle (degree) 101 90.8 89.4 90.8 88.3 86.4 86.5 86.3 86.8 85.9 83.9
Run#2 CO2 Exposure Time (min.) Conact Angle (degree) 0 97.5 9 96.7 11 95.2 17 74.8 23 72.8 25 72.8 28 73 32 73 34 69.2 36 69.1 39 69.4 44 69.4 52 69.3 76 69.3 83 69.3 89 69.3
15
Table 4: Initial and minimum contact angles with stabilization time Run No. 1 2
CO2 θi Concentration (mole %) (Degrees) 0.0004 101.0 0.0008 97.0
16
θmin (Degrees) 83.9 69.3
tsb (Minutes) 44 52
Lists o of Figuress
Figu ure 1: Residu ual oil saturaation variatioon with conttact angle
17
Figgure 2: Conttact angle vaariation with CO2 exposuure time
18
Figure 3: Diagram oof the experim mental set-up up
19
Figu ure 4: Core slice-hanger assembly a
20
Fig gure 5: Visuual cell compponents
21
Figure 6: Shape of the oil drop (a) before CO2 injection (b) after 44 minutes of CO2 exposure
22
Figure 7: Plot showin ng raw experrimental dataa for Run # 1 and Run # 2
23
Figgure 8: Plot showing dim mensionless experimentaal data for Run # 1 and Run R #2
24
Figure 99: Dimensioonless experiimental data on semi-logg scale with fitting curvee for Run # 1 and Run # 2
25
Research highlights 1. An experiment was conducted to capture the wettability alteration during CO2 flooding. 2. An empirical model is developed to measure wettability alteration on continuous basis during CO2 immiscible displacement. 3. Increasing CO2 concentration in the brine results in larger alteration of wettability. 4. The oil-brine-rock contact angle decreases to a new stable value after a relatively short period of time. 5. The change in contact angle can be modeled by an asymptotic-exponential function of time.
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An experimental Investigation of wettability alteration during CO2 immiscible flooding Saad M. Al-Mutairi, Sidqi A. Abu-Khamsin, Taha M. Okasha, Saudi Aramco, M. Enamul Hossain
www.elsevier.com/locate/petrol
PII: DOI: Reference:
S0920-4105(14)00125-9 http://dx.doi.org/10.1016/j.petrol.2014.05.008 PETROL2657
To appear in:
Journal of Petroleum Science and Engineering
Received date: 6 June 2012 Revised date: 28 April 2014 Accepted date: 17 May 2014 Cite this article as: Saad M. Al-Mutairi, Sidqi A. Abu-Khamsin, Taha M. Okasha, Saudi Aramco, M. Enamul Hossain, An experimental Investigation of wettability alteration during CO2 immiscible flooding, Journal of Petroleum Science and Engineering, http://dx.doi.org/10.1016/j.petrol.2014.05.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
An Experimental Investigation of Wettability Alteration during CO2 Immiscible Flooding Saad M. Al-Mutairi, KFUPM, Sidqi A. Abu-Khamsin, KFUPM, Taha M. Okasha, Saudi Aramco and M. Enamul Hossain*, KFUPM Abstract Wettability has been recognized as one of the key parameters controlling the remaining oilin-place. The knowledge of reservoir wettability is essential to understand the fluid displacement mechanisms, and to develop strategies for achieving higher recovery factors. One of the effective approaches to enhance oil recovery significantly is wettability alteration which has been investigated extensively in the literature. This paper investigates wettability alteration experimentally, on continuous basis, during CO2 immiscible flooding. Measurements of the contact angle between oil, carbonated brine and a slice of rock cut from a carbonate core plug were conducted. The results indicate that the rock wettability is altered from oil-wet to intermediate-wet when the oil/rock system is exposed to dissolved CO2. The extent of wettability alteration is controlled by CO2 exposure time; as such time is increased, alteration of wettability progresses towards an apparent limit. It is also found that as the CO2 concentration increases in the brine, wettability alteration increases. Based on the experimental finding, an empirical model is developed to describe such continuous wettability alteration. The findings of this study can be applied to the cases where CO2 is injected in a watered out, oil-wet reservoir at a pressure below the miscibility pressure. Keyword: oil-wet reservoir, exposure time, contact angle, reservoir modeling, enhanced oil recovery Introduction Wettability alteration is an effective approach to enhance oil recovery significantly. Buckley et al., (1998) summarized four main factors affecting wettability alteration which are: oil composition, brine chemistry, rock surface mineralogy and the system temperature, pressure and saturation history. The adsorption and the deposition of organic polar components in the crude oil can alter most of the rock surface chemistry. Brine salinity and pH strongly affect the charge of the rock surface where the rock surface becomes positively charged when the pH is decreased and the rock surface becomes negatively charged when the pH is increased. The solubility of wettability-altering compounds tends to increase when temperature and pressure are elevated. Wettability alteration during CO2 flooding has been investigated extensively in the literature through core experiments (Stalkup, 1970; Tiffin and Yellig, 1983; Maini et al., 1986; Potter, 1987; Lin and Huang, 1990; Rao et al., 1992; Vives et al., 1999; Zekri et al., 2007; Fjelde and Asen, 2010). Investigators have proved experimentally that the wettability can be altered because of CO2 injection. Also, the laboratory experiments showed that the interfacial tension reduction may contribute to wettability alteration (Chalbaud et al., 2006; Shariat et al., 2012). On the other hand, a limited number of modeling studies on wettability alteration during CO2 displacement is documented in the literature (Tehrani et al., 2001; van Dijke and Sorbie, 2002; Farhadinia and Delshad, 2010; Ju et al., 2010; Kalaei et al., 2012; Mutairi et al., 2012). Most of the documented experiments or modeling works conducted on wettability alteration were devoted to CO2 miscible displacement where a super-critical CO2 phase comes into 1
*Corresponding authors: Dr. M. Enamul Hossain, Department of Petroleum Engineering, College of Engineering Science, King Fahd University of Petroleum & Minerals, Dhahran 31261, KFUPM Box: 2020, Saudi Arabia. Tel: 0096638602305 (O), Fax: 0096638604447. Email: [email protected], [email protected]
contact with w the reservoir fluidss. Work on displacemen nt by CO2 uunder low pressures p in a watered out reservoiir has not been b reporteed. This papper reports tthe results of o a study on o wettabilitty alterationn on a conntinuous bassis under suuch conditioons. The stuudy involveed experimeents to meassure the oil/bbrine contactt angle on a core slice ccut from a carbonate corre in the preesence of CO O2. The conttact angle waas measured at different times until equilibrium e is attained. The results were used to t develop a simple moddel that preddicts wettabiility alteratioon with timee. ment of Moodel on Wetttability Alteeration Developm Core flooding experriments showed that thhe maximum m oil recoveery apparen ntly occurs in i ( annd Mungan, 1971; Lorennz et al., 19774). Strong oil o neutral or slightly oill-wet cores (Morrow pies the smaall wettabilitty results inn low oil reecovery becaause the weetting phase (oil) occup pores, whhich leads to o a high resiidual oil satuurations. In contrast, c thee residual oill saturation in i intermed diate-wet rocks decreasses if wateer shares thhose small pores. Theerefore, it is theoreticaally plausiblle to speculaate that the rresidual oil saturation w will follow an exponential relationshhip with the rock wettabbility as depicted in Fig. 1.
Figu ure 1: Residu ual oil saturaation variatioon with conttact angle w an oil-w wet porous medium fullly saturated with water at residual oil o saturationn; Starting with and if wee expose thee system to CO C 2 gas, the wettability is expected to graduallyy change from m oil-wet to intermediaate-wet as CO C 2 diffusess through thhe water andd oil to the rock surfacce. c ons, the rate of o Since forr a given sysstem diffusioon is controllled by the diifference in concentratio diffusionn would declline exponenntially with ttime as such difference ddiminishes (Grogan et all., 1986). As A the channge in contaact angle iss directly reelated to thhe concentraation of CO O2 moleculees at the oil//rock surfacee, and as the rate of buuild- up of such concenttration is alsso diminishiing exponenntially with time, the coontact angle would thenn be expecteed to decreasse exponenttially with CO C 2 exposurre time as conceptually c y depicted inn Fig. 2. However, H succh decrease would apprroach a certaain new anggle asymptottically as thee contact anggle cannot go g below zeero.
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Figgure 2: Conttact angle vaariation with CO2 exposuure time c the relationshipps between wettability w annd CO2 expo osure time caan Based onn the above concept, be modelled as follow ws:
θ = ae−bt + c
(1)
Where θ : Contaact angle
t : CO2 exxposure timee a, b and c : Constantss related to roock and fluidd compositioons as well aas aging history and process parameters. p Inspectioon of Eq. 1 reeveals that c is the ultim mate contact angle a ( θmin ) reached at in nfinite exposuree time ( i.e. t → ∞ ) . The constant c a theen becomes the difference between the t initial contact angle a ( θi ) annd θmin . The constant b iss related to the t time wheen the contacct angle is practicallly equal to θmin . Such tim me shall be ccalled stabiliization time ( tsb ) and, thhus, b can bee defined as a b = ξ / tsb where ξ is a constant w whose signifiicance shall become b eviddent shortly.
d ss form as: Employinng all the abbove parametters, Eq. 1 caan then be reewritten in dimensionles
θ − θ min θi − θ min −ξ t / t = e θ min θ min
(22)
sb
3
Defining dimensionleess contact angle a as θ D =
θ −θ min t an nd dimensionnless time ass t D = , Eqq. θ min tsb
2 becomees:
θ D = θ Di e−ξ t
(3)
D
Where
θ Di =
θ i −θ min θ min
All consttants in Eq. 2 can be estiimated experrimentally ass is presented below. Experim mental Set-up The expeerimental sett-up consistss of eight coomponents as a shown in Fig. 3. A CO O2 cylinder is connected to a 60-ccc visual celll through a regulator to control CO O2 injection. The pressurre perature of the t visual ceell are contrrolled and monitored m thrroughout thee experimennt. and temp The visual cell is maade of stainless steel andd can withsttand high preessures and temperaturees. h is screewed to the roof of the cell c on the innside to whicch a rock sliice is attacheed A steel hanger (Fig. 4). The visual cell c is fitted with w a glass window to allow a monitooring the low wer surface of o mera is placeed horizontaally to the leevel of the visual v cell too allow takinng the rock slice. A cam wnloads the pphotographs to a personnal photograaphs of the contents of thhe cell. The camera dow computerr where theyy are analyzzed by speccial softwaree to estimatte the contacct angle. Thhe Drop Imaage softwaree is providedd by the mannufacturer off the pendentt drop IFT sy ystem.
Figure 3: Diagram oof the experim mental set-up up
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Figu ure 4: Core slice-hanger assembly a
mental Proceedure Experim The carbbonate core plug p was cleeaned and drried in an ovven at 90 °C. The plug was w then fullly saturatedd with brine using u the vaacuum methood followed by floodingg the plug wiith dead oil in i a core-floooding setupp until no brrine is produuced. The pllug’s porositty, pore voluume and final oil and water w saturatiions were thhen computedd by mass balance on oiil and water. Properties of o the rock and a fluids em mployed in the t experimeent are preseented in Tablles 1 and 2. Table-1: Properties of o the rock annd fluids em mployed in thhe experimennt Properrty Oill density (g/ccc) Oill viscosity (ccP) Briine density (g/cc) Briine viscosityy (cP) Corre permeabillity (mD) Corre porosity ((%)
Value 0.85 0.71 0.99 0.56 5 15
Table-2: Brrine composiition Salt Sodium m Chloride (NaCl) Calciuum Chloride (CaCl2.2H2O) Magnesium Chlorride (MgCl2..6H2O)
Concentrration g/L 166.7 3..62 1..28
0 cm thick k, 2.3 cm in diameter d waas immediateely cut from the core pluug A thin coore slice of 0.5 after the dead oil dissplacement. The slice was w then subm merged in thhe same oil and aged in a 8 oC and 20 000 psig for two weeks to t ensure oil wettability y. After agingg, titanium cylinder at 85 o the surfacce of the corre slice was grinded to a uniform plaane to allow accurate meeasurement of the contaact angle. The T polishedd core slice was then ag ged in the ssame oil unnder the sam me conditionns to ensuree oil wettabiility. The coore slice waas then attacched to the hanger usinng special eppoxy cemen nt which has high resistaance to temperature (Fig. 4). The han nger was theen 5
mounted inside the visual v cell. The T cell wass then filled completely with brine and heated to t d oil was thhen introduceed to the ceell 70 ºC annd pressurizeed to 500 psig. A drop of the dead through a vertical neeedle fitted to t the bottom m of the celll. The needlle was positiioned directlly below the core slice so that wheen the drop eenters the ceell it rises thhrough the brine and ressts wer surface of the core slice s (Fig. 5)). The contacct angle betw ween the rocck surface, thhe on the low oil drop and a the surroounding brinne was then m measured.
Fig gure 5: Visuual cell compponents 20 ppm) waas then rapid dly charged to t CO2 gas (99.5% puree with moisture contentt less than 12 mined level (about 1000 psig); CO O2 the cell until the ceell’s pressurre rose to a pre-determ opped. When the cell’s ppressure droopped back too 500 psig, which w usuallly injection was then sto nds, indicatinng complete dissolution of CO2 in tthe brine, hiigh-resolutioon took about 15 secon o drop werre then takeen periodicallly until no noticeable change c in thhe photograaphs of the oil shape off the drop was w observed. The phottographs weere then anaalyzed and values v of thhe contact angle a versus the drop’s exposure e tim me to the carb bonated brine were recorrded. Figure 6 depicts how h the shappe of the oil drop d changed with time. gle using thhe pendent drop methhod is a pu ure numerical Calculatiion of the contact ang techniquee. The cameera’s view fiinder shows a horizontaal line on the screen alo ong which thhe solid surfface is alignned. The filteer routine thhen gives a properly p aliggned drop profile and thhe contact angle a is easilly calculatedd by numeriical derivatioon of the proofile at the contact c poinnt. Because of reflection n in the substrate and soome diffracttion, 2 to 3 data points closest to thhe p are negglected. In th he Drop Imaage software the drop profile p is esttablished by a contact point travellingg secant method with liinear extrapoolation to thhe contact ppoint. This method m seem ms more rob bust than the ones that have been tried out. Itt gives valuees between a pure lineaar derivation, which unnderestimates the contacct angle, and d higher ordder (polynom mial) methodds o the angle. that usuaally tend to overestimate
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Figure 6: Shape of the oil drop (a) before CO2 injection (b) after 44 minutes of CO2 exposure Results and Discussion Two runs were conducted at two different brine CO2 concentrations (0.0004 mole percent for Run # 1 and 0.0008 mole percent for Run # 2). The CO2 concentration was calculated by volumetric balance on the cell’s contents. Table 3 lists the data of both runs, which are also plotted in Figure 7. Since the CO2 was completely dissolved in the brine as indicated by the rapid drop in the cell’s pressure after charging it with CO2, the results demonstrate that the rock wettability in both runs was altered when the rock was exposed to carbonated brine. Wettability alteration is believed to be caused by diffusion of CO2 from the brine into the oil droplet. Once CO2 molecules reach the rock surface contacted by the oil droplet, these molecules start replacing hydrocarbon molecules - mostly asphaltenes – that are adsorbed on the surface and initially causing it to be oil wet. This gradual replacement causes the rock surface to shift its wettability towards water. Diffusion of CO2 from the brine to the rock surface that is covered by the oil droplet involving any route other than through the oil droplet is not realistic because it would involve diffusion through the oil-saturated rock matrix, which is an extremely slow process. In Run # 1, the contact angle decreased from 101º initially to reach a stable value of about 83.9º after 44 minutes of exposure to the carbonated brine. The change in contact angle shows that the wettability of the core slice was altered from slightly oil-wet to intermediatewet. In Run # 2, the stable value appeared to be 69.3 º and was attained in 52 minutes. When the exposure time was extended to 89 minutes in this run, no change was observed in the angle confirming the existence of a stable value in the contact angle. The trend in both data sets reveals an asymptotic-exponential relationship between the contact angle and exposure time. The initial decrease in the angle was rapid followed by a gentle trend towards a stable value. Table 3: Variation of the contact angle with time
CO2 Exposure Time 0 6 8 16 21 23 28 34 40 43 44
Run#1 Conact Angle (degree) 101 90.8 89.4 90.8 88.3 86.4 86.5 86.3 86.8 85.9 83.9
Run#2 CO2 Exposure Time (min.) Conact Angle (degree) 0 97.5 9 96.7 11 95.2 17 74.8 23 72.8 25 72.8 28 73 32 73 34 69.2 36 69.1 39 69.4 44 69.4 52 69.3 76 69.3 83 69.3 89 69.3
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Figure 7: Plot showin ng raw experrimental dataa for Run # 1 and Run # 2 The relattively short time t (less thhan one hourr) it took to complete thhe wettabilityy alteration as a observedd in the twoo runs is neggligible in terms t of thee time scale of field appplications. In I flooding projects whhere the CO2 flood frontt advances at a a speed of o feet per daay wettabilitty alterationn is expected to appear almost insttantaneouslyy. However, in watered--out reservooir rock wheere oil existss as dropletss trapped in small poress with limiteed access by y the reservooir brine, CO O2 gas needss to diffuse through t the water phasee then the oill droplets beefore reachinng the rock surface. At low CO2 cooncentrations, this diffussion processs might takee considerablly me to compllete, causing much sloweer wettabilityy alteration. longer tim d on the CO2 conncentration of o The dataa of Figure 7 also revealls that the sttable value depends the brinee in contact with the oiil with a higgher concen ntration caussing a largeer drop in thhe contact angle. a Howeever, the ex xposure timee needed to reach a staable angle appears a to be b slightly dependent d up pon CO2 con ncentration. One can theen speculate that under the t conditionns of this experiment, where w oil iss surroundedd by brine, diffusion off CO2 into the t oil is faast w concentrattions. It rem mains to bee seen wheether at higgh enough even at rellatively low b altered too a water-w wet state. Taable 4 summ marizes Eq. 2 concentraations the rock could be parameteers as extractted from the data. Table 4: 4 Initial and minimum contact anglees with stabillization timee Ru un Noo.
C 2 CO Conceentration (moole %)
1 2
0.0 0004 0.0 0008
θi
θmin
tsb
(Degrees) 101.0 97.0
(Degrees) 83.9 69.3
(Minutes) 44 52
8
Based onn the parameeter values listed in Tablee 4, θ D was computed aand plotted vs. v t D for botth runs (Fig g. 8). All dataa points fall within one band b indicatting a commoon value of ξ for both runs. Takking log e off both sides of o Eq. 3 yieldds:
loog e θ D = log e θ Di − ξ tD
(4))
T four Re-plotting Fig. 8 wiith semi-log axes (Fig. 9) shows a reeasonably linnear trend. The outlying data points are a attributedd to experim mental error; however, thhe bulk of thee data does fall on thhe same trend d. Excluding g those four data points, the slope off this line is 1.39 1 which is the valuee of ξ for the conditionss of this expeeriment.
Differenttiating Eq. 3 with respecct to tD yieldds: dθ D = −θ Diξ e −ξ tD dt dD
or
dθ D = −ξθ D dt dD
(5))
Equationn 5 shows thaat ξ controls the rate off decline of th he dimensionnless contacct angle withh dimensioonless time. We W can specculate that thhis parameterr is similar for f all other concentraations of CO O2, which maakes predictiing other min nimum contact angles poossible for the rock/oil system of o this study.
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Figgure 8: Plot showing dim mensionless experimentaal data for Run R # 1 and Run R #2
Figure 9: 9 Dimensioonless experiimental data on semi-logg scale with ffitting curvee for Run # 1 and Run # 2
Conclusiions t study caan be relatedd to cases wh here CO2 is injected in a watered ouut, The significance of this oil-wet reeservoir at a pressure beelow the misscibility presssure. CO2 diiffusion throough the brinne can alterr the rock wettabilityy and rendeer the residdual oil m mobile. In miscible m CO O2 displacem ment processses, such pheenomenon can still occu ur when CO2 fingers advance ahead of o the CO2 slug s and conntact residuaal oil under im mmiscible conditions. c Itt is worth meentioning that more con ntact angle measuremennt experimennts need to be conductted to establlish a generral wettabilitty alteration model – Eqq. (1) – fittedd for differennt rock/fluid systems. Conclusions from thiis study can be summarized as follow ws: C 2 causes alteration of the rocck 1. Exposing carboonate rock to brine ccontaining CO m an oil-wet to t an intermeediate-wet sttate. wetttability from 2. Incrreasing CO2 concentratio on in the brinne results in larger alteraation of wetttability. 3. The oil-brine-roock contact angle a decreaases to a new w stable valuue after a reelatively shoort od of time. perio The channge in contacct angle can be possibly modeled by an exponenntial function n of time where a simple s dimensionless rellationship is controlled by b a parametter, ξ , comm mon to all CO2 conccentrations. 4. The significancee of this expperiment cann be related d to cases whhere CO2 is injected in a he miscibilityy pressure. wateered out, oil--wet reservooir at a pressuure below th Referencces 10
1. Buckley J.S., Liu Y and Monsterleet S: “Mechanisms of Wetting Alteration by Crude Oils,” paper SPE 37230, SPE Journal 3, no. 1 (March 1998): 54–61. 2. Chalbaud, C., Robin, M. and Egermann, P., “Interfacial Tension Data and Correlations of Brine/CO2 System Under Reservoir Conditions”, SPE 102918, presented at the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 24-27 September. 3. Farhadinia, M. and Delshad M., 2010. Modeling and Assessment of Wettability Alteration Processes in Fractured Carbonates using Dual Porosity and Discrete Fracture Approaches, paper SPE 129749, presented at the 2010 SPE Improved Oil Recovery Symposium, Tulsa, Oklahoma, USA, April 24-28. 4. Fjelde, Ingebret and Asen, Siv Marie, 2010. Wettability Alteration during Water Flooding and Carbon Dioxide Flooding of Reservoir Chalk Rocks. paper SPE 130992, presented at SPE EUROPEC/EAGE Annual Conference and Exhibition, Barcelona, Spain, June 1417. 5. Grogan, A. T., Pinczewski, W. V., Ruskhauff, G. J., and Orr, F. M. Jr., “Diffusion of Carbon Dioxide at Reservoir Conditions: Models and Measurements”, paper SPE/DOE 14897 presented at the 1986 SPE/DOE Fifth Symposium on Enhanced Oil Recovery, Tulsa OK April 1986). 6. Lin, Eugene and Huang, Edward, 1990. The Effect of Rock Wettability on Water Blocking during Miscible Displacement. SPE Reservoir Engineering, May. 7. Lorenz, P. B. Donaldson, E.C. and Thomas, R.D., “Use of Centrifugal Measurements of Wettability to Predict Oil Recovery,” report 7873, USBM, Bartlesville Energy Technology Center (1974). 8. Kalaei, Hosein, Green, Don and Willhite, Paul, “A New Dynamic Wettability Alteration Model for Oil-Wet Cores During Surfactant Solution Imbibition,” paper SPE 153329 presented at the 2012 SPE Improved Oil Recovery Symposium, Tulsa, Oklahoma, USA, April 14-18. 9. Maini, B., Ionescu, E. and Batycky, J. 1986. Miscible Displacement of Residual Oil – Effect of Wettability on Dispersion in Porous Media. JCPT, May-June, Montreal. 10. Morrow, N. R. and Mungan, N., “Wettability and Capillarity in Porous Media.” Report RR-7, Petroleum Recovery Research Inst., Calgary (Jan. 1971) 11. Mutairi, S. M., Abu-Khamsin, S. A. and Enamul Hossain, M., “A Novel Approach to Handle Continuous Wettability Alteration during Immiscible CO2 Flooding Process”, paper SPE 160638 presented the Abu Dhabi International Petroleum Exhibition & Conference held in Abu Dhabi, UAE, 11–14 November 2012. 12. Potter G. F., 1987. The effects of CO2 Flooding on Wettability of West Texas Dolomitic Formations. paper SPE 16716, presented at the Annual Technical Conference and Exhibition, Dallas, TX, September 27-30. 13. Shariat, A., Moore, R., Mehta, S., Van Fraassen, K., Newsham, K. and Rushing, J., “Laboratory Measurements of CO2-H2O Interfacial Tension at HP/HT Conditions: Implactions for CO2 Sequestration in Deep Aquifers”, paper CMTC 150010, presented at the Carbon Management Technology Conference, Orlando, USA, 7-9 February 2012. 14. Stalkup, F.I., 1970. Displacement of Oil by Solvent at High Water Saturation. SPEJ (December) 337. 15. Rao, Dandina, Girard, M. and Sayegh, S., 1992. The Influence of Reservoir wettability on Waterflood and Miscible Flood Performance. JCPT, June, Volume 31, No. 6. 16. Tehrani, D., Danesh, A., Sohrabi, M. and Henderson, G., 2001. Improved Oil Recovery from Oil-Wet and Mixed-Wet Reservoirs by Gas Flooding, Alternately with Water. Presented to IEA Annual Workshop & Symposium, Vienna, September.
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17. Tiffin, D. L. and Yellig, W. F., 1983. Effects of Mobile Water on Multiple-Contact Miscible Gas Displacement. SPEJ (June) 447. 18. van Dijke, M.I.J. and K.S. Sorbie, 2002. Pore-Scale Network Model for Three-Phase Flow in Mixed-Wet Porous Media. Physical Review E, 66(4), pp 046302. 19. Vives, M., Chang, Y., Mohanty, K., 1999. Effect of Wettability on Adverse-Mobility Immiscible Floods,” SPE Journal, September. 20. Zekri, A., Shedid, S. and Almehaideb, R., 2007. Possible Alteration of Tight Limestone Rocks Properties and the Effect of Water Shielding on the Performance of Supercritical CO2 Flooding for Carbonate Formation. paper SPE 104630, presented at the SPE Middle East Oil & Gas Show and Conference, Bahrain, March 11-147.
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Lists of Tables Table-1: Properties of the rock and fluids employed in the experiment Property Oil density (g/cc) Oil viscosity (cP) Brine density (g/cc) Brine viscosity (cP) Core permeability (mD) Core porosity (%)
13
Value 0.85 0.71 0.99 0.56 5 15
Table-2: Brine composition Salt Sodium Chloride (NaCl) Calcium Chloride (CaCl2.2H2O) Magnesium Chloride (MgCl2.6H2O)
Concentration g/L 16.7 3.62 1.28
Table 3: Variation of the contact angle with time
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CO2 Exposure Time 0 6 8 16 21 23 28 34 40 43 44
Run#1 Conact Angle (degree) 101 90.8 89.4 90.8 88.3 86.4 86.5 86.3 86.8 85.9 83.9
Run#2 CO2 Exposure Time (min.) Conact Angle (degree) 0 97.5 9 96.7 11 95.2 17 74.8 23 72.8 25 72.8 28 73 32 73 34 69.2 36 69.1 39 69.4 44 69.4 52 69.3 76 69.3 83 69.3 89 69.3
15
Table 4: Initial and minimum contact angles with stabilization time Run No. 1 2
CO2 θi Concentration (mole %) (Degrees) 0.0004 101.0 0.0008 97.0
16
θmin (Degrees) 83.9 69.3
tsb (Minutes) 44 52
Lists o of Figuress
Figu ure 1: Residu ual oil saturaation variatioon with conttact angle
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Figgure 2: Conttact angle vaariation with CO2 exposuure time
18
Figure 3: Diagram oof the experim mental set-up up
19
Figu ure 4: Core slice-hanger assembly a
20
Fig gure 5: Visuual cell compponents
21
Figure 6: Shape of the oil drop (a) before CO2 injection (b) after 44 minutes of CO2 exposure
22
Figure 7: Plot showin ng raw experrimental dataa for Run # 1 and Run # 2
23
Figgure 8: Plot showing dim mensionless experimentaal data for Run # 1 and Run R #2
24
Figure 99: Dimensioonless experiimental data on semi-logg scale with fitting curvee for Run # 1 and Run # 2
25
Research highlights 1. An experiment was conducted to capture the wettability alteration during CO2 flooding. 2. An empirical model is developed to measure wettability alteration on continuous basis during CO2 immiscible displacement. 3. Increasing CO2 concentration in the brine results in larger alteration of wettability. 4. The oil-brine-rock contact angle decreases to a new stable value after a relatively short period of time. 5. The change in contact angle can be modeled by an asymptotic-exponential function of time.
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