ASPHALTENE PRECIPITATION AND ITS EFFECTS ON CO 2 -ENHANCED OIL RECOVERY (CO 2 -EOR) Yongan (Peter) Gu, Professor, Ph.D., P.Eng.

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1 ASPHALTENE PRECIPITATION AND ITS EFFECTS ON CO 2 -ENHANCED OIL RECOVERY (CO 2 -EOR) Yongan (Peter) Gu, Professor, Ph.D., P.Eng. Petroleum Technology Research Centre (PTRC) Petroleum Systems Engineering Faculty of Engineering and Applied Science University of Regina Regina, Saskatchewan S4S 0A2 CANADA Tel: (306) , Fax: (306) Peter.Gu@Uregina.Ca 32 nd Annual IEA EOR Symposium and Workshop (Monday, October 17, 2011) 1

2 Introduction OUTLINE Research Objectives Experimental Experimental Results Conclusions Future Work Acknowledgments 2

3 INTRODUCTION In a typical light or medium oil reservoir, there is still 50 60% of the original-oil oil-in-place (OOIP) after water flooding. Among all the enhanced oil recovery (EOR) methods for the light and medium oil reservoirs, CO 2 flooding has been successfully conducted to a large extent. CO 2 flooding is largely controlled by the mutual interaction between the reservoir oil and CO 2, which plays an important role in developing the multi- contact or dynamic miscibility. 3

4 INTRODUCTION (cont d) During a CO 2 -based oil recovery process, asphaltene precipitation occurs if a sufficient amount of CO 2 dissolves into oil, which significantly changes the physicochemical properties of the original crude oil. Considering both detrimental and beneficial effects, asphaltene precipitation may cause reservoir plugging and wettability alteration, while the desaphalted crude oil becomes less viscous and much easier to be recovered. 4

5 RESEARCH OBJECTIVES To characterize the properties of precipitated asphaltenes and remaining maltenes from a medium crude oil CO 2 or n- pentane system. To study the mutual interaction process between each of three different crude oils and CO 2, including the determination of the onset pressure of asphaltene precipitation and minimum miscibility pressure (MMP) and the observations of oil swelling and initial quick light-components extraction. To study the effects of asphaltene precipitation through CO 2 coreflood tests by measuring the oil recovery factor, oil effective permeability reduction, and asphaltene content of the produced oil. 5

6 EXPERIMENTAL Materials Physicochemical Analysis Onset of Asphaltene Precipitation Interfacial Tension (IFT) Measurement CO 2 Coreflood Tests 6

7 Materials Crude oils: Oilfield Joffre Viking Pembina Cardium Weyburn Weight percentage (wt.%) CO 2 EOR stage Intermediate Early Intermediate Crude oil type Light Light Medium 27 o C (g/cc) o C (mpa s) Specific gravity ( o API) Molecular weight (g/mol) Asphaltene content (wt.%) Joffre Viking (C 50+ = wt.%) Pembina Cardium (C 50+ = wt.%) Weyburn (C 50+ = wt.%) Carbon number 7

8 Physicochemical Analysis High-pressure densitometer Cone-plate viscometer Freezing-point osmometer Varian 6500 GC with a flame ionization detector (FID) Nuclear magnetic resonance measurement (NMR) Fourier transform infrared measurement (FTIR) 8

9 Onset of Asphaltene Precipitation Personal computer Syringe pump Microscope & camera P Saturation cell Temperature controller CO 2 at P, T Crude oil Crude Oil Light source CO 2 cylinder Saturation cell The experimental set-up used for determining the onset pressure of the asphaltene precipitation from a crude oil CO 2 system. 9

10 Interfacial Tension (IFT) Measurement Hydraulic oil Positive displacement pump CO 2 Crude oil P Syringe pump Temperature controller Pressure cell Light source CO 2 at P, T Microscope & camera Personal computer Vibration-free table The axisymmetric drop shape analysis (ADSA) set-up used for measuring the dynamic and equilibrium IFTs of a crude oil-co 2 system. 10

11 CO 2 Coreflood Setup Fan Air bath Fan CO 2 Crude Oil Brine Automatic pump Water Differential pressure transducer P Thermocouple Manual displacement pump P Coreholder High-pressure coreholder P Electric heater Temperature controller P N 2 cylinder Back-pressure regulator Personal computer Gas flow meter Oil sample collector To atmosphere 11

12 EXPERIMENTAL RESULTS Characterization of Asphaltenes and Maltenes Onset Pressure of Asphaltene Precipitation Equilibrium IFT and MMP Oil-Swelling Effect and Light-Components Extraction Summary of Four Important Onset Pressures Immiscible and Miscible CO 2 Coreflood Tests 12

13 Characterization of Asphaltenes and Maltenes (a) CO 2 -asphaltenes (b) C 5 -asphaltenes Digital photographs of (a) CO 2 -asphaltenes and (b) C 5 -asphaltenes. 13

14 Characterization of Asphaltenes and Maltenes (cont d) Test sample Density (kg/m 3 ) Molecular weight (g/mol) Medium crude oil CO 2 -maltenes C 5 -maltenes CO 2 -asphaltenes C 5 -asphaltenes Test sample f a ( 1 H NMR) f a ( 13 C NMR) n carbon ( 1 H NMR) R (FTIR) R 1 (FTIR) Medium crude oil CO 2 -maltenes C 5 -maltenes CO 2 -asphaltenes C 5 -asphaltenes

15 Onset Pressure of Asphaltene Precipitation Joffre Viking light crude oil-co2 system 1 mm P = 3.0 MPa P = 5.0 MPa P = 5.4 MPa P = 5.5 MPa P = 5.6 MPa P = 3.0 MPa Digital images of asphaltenes precipitated from Joffre Viking light crude oil CO2 system on the acrylic window of the high-pressure saturation cell and T = 27 oc. 15

16 Onset Pressure of Asphaltene Precipitation (cont d) Pembina Cardium light crude oil CO 2 system 1 mm P = 3.0 MPa P = 4.4 MPa P = 4.8 MPa P = 5.2 MPa P = 5.6 MPa P = 3.0 MPa Digital images of asphaltenes precipitated from Pembina Cardium light crude oil CO 2 system on the acrylic window of the high-pressure saturation cell and T = 27 o C. 16

17 Onset Pressure of Asphaltene Precipitation (cont d) Weyburn medium crude oil CO 2 system 1 mm P = 3.0 MPa P = 3.5 MPa P = 3.8 MPa P = 4.5 MPa P = 5.6 MPa P = 3.0 MPa Digital images of asphaltenes precipitated from Weyburn medium crude oil CO 2 system on the acrylic window of the high-pressure saturation cell and T = 27 o C. 17

18 Equilibrium IFTs and MMP Joffre Viking light crude oil CO 2 system Equilibrium interfacial tension γ eq (mj/m 2 ) I I: II: III: MMP= MPa γ eq = 3.35P (2.4 MPa<P<4.6 MPa) R 2 =0.996 γ eq = 5.18P (5.0 MPa<P<6.4 MPa) R 2 =0.988 γ eq = 1.48P (6.4 MPa<P<9.3 MPa) R 2 = Equilibrium pressure (MPa) II III P=2.4 MPa P=3.5 MPa P=4.2 MPa P=4.6 MPa P=5.0 MPa P=5.5 MPa P=6.0 MPa P=6.4 MPa P=7.2 MPa P=8.0 MPa P=9.3 MPa P max =10.0 MPa Measured equilibrium IFTs of Joffre Viking light crude oil CO 2 system at different equilibrium pressures and T = 27 o C. 18

19 Equilibrium IFTs and MMP (cont d) Pembina Cardium light crude oil CO 2 system Equilibrium interfacial tension γ eq (mj/m 2 ) I MMP= MPa I: II: III: γ eq = 3.47P (2.4 MPa<P<5.5 MPa) R 2 =0.988 γ eq = 9.06P (6.2 MPa<P<7.2 MPa) R 2 =0.987 γ eq = 0.59P+7.68 (7.2 MPa<P<11.0 MPa) R 2 =0.988 II III Equilibrium pressure (MPa) P=2.4 MPa P=3.5 MPa P=4.2 MPa P=5.0 MPa P=5.5 MPa P=6.2 MPa P=6.4 MPa P=6.6 MPa P=7.2 MPa P=8.0 MPa P=9.3 MPa P=11.0 MPa P max =13.0 MPa Measured equilibrium IFTs of Pembina Cardium light crude oil CO 2 system at different equilibrium pressures and T = 27 o C. 19

20 Equilibrium IFTs and MMP (cont d) Weyburn medium crude oil CO 2 system Equilibrium interfacial tension γ eq (mj/m 2 ) I MMP=9.3 MPa I: II: γ eq = 2.26P (2.4 MPa<P<6.4 MPa) R 2 =0.961 γ eq = 0.60P (6.4 MPa<P<14.0 MPa) R 2 = Equilibrium pressure (MPa) II P=2.4 MPa P=3.5 MPa P=4.2 MPa P=4.6 MPa P=5.0 MPa P=5.5 MPa P=6.0 MPa P=6.4 MPa P=7.2 MPa P=8.0 MPa P=9.3 MPa P=11.0 MPa P=12.8MPa P=14.0 MPa P max =18.2 MPa Measured equilibrium IFTs of Weyburn medium crude oil CO 2 different equilibrium pressures and T = 27 o C. system at 20

21 Oil-Swelling Effect and Light-Components Extraction Initial oil-swelling Effect: Joffre Viking Pembina Cardium Weyburn t = 0 s V = mm 3 t = 0 s V = mm 3 t = 0 s V = mm 3 t = 30 s V = mm 3 t =30 s V = mm 3 t = 30 s V = mm 3 t = 60 s V = mm 3 t = 60 s V = mm 3 t = 60 s V = mm 3 Digital images of the pendant oil drop in CO 2 at P = 3.5 MPa and T = 27 o C during the initial oil swelling process and subsequent weak light-components extraction. 21

22 Oil-Swelling Effect and Light-Components Extraction (cont d) Initial quick light-components extraction: Joffre Viking Pembina Cardium Weyburn t = 0 s t = 0 s t = 0 s t = 30 s V = mm 3 t = 30 s V = mm 3 t = 30 s V = mm 3 t = 100 s V = mm 3 t = 100 s V = mm 3 t = 100 s V = mm 3 Digital images of the pendant oil drop in CO 2 at P = 7.2 MPa and T = 27 o C during the Initial quick light-components extraction and subsequent weak light-components extraction. 22

23 Summary of Four Important onset pressures Four onset pressures for three different crude oil CO 2 systems at T = 27 o C Oilfield Joffre Viking Pembina Cardium Weyburn P asp (MPa) P ext (MPa) MMP (MPa) P max (MPa) Notes: P asp : P ext : MMP: P max : onset pressure of the asphaltene precipitation onset pressure of the initial quick light-components extraction minimum miscibility pressure determined by applying the VIT technique miscibility pressure between the heavy components of the original crude oil and CO 2, which is close to the so-called first-contact miscibility pressure 23

24 Immiscible and Miscible CO 2 Coreflood Tests Immiscible and miscible CO 2 coreflood tests (Pembina Cardium oil): Test No. φ (%) k (md) S oi (%) S wc (%) P (MPa) Water RF (%) CO 2 RF (%) Total RF (%) w asp (wt.%) P 1 (kpa) P 2 (kpa) k o /k o (%) Notes: *All of the coreflood tests were conducted at T = 27 o C. * P 1 : Differential pressure between the inlet and outlet of the coreholder during the initial original crude oil injection before CO 2 flooding. * P 2 : Differential pressure between the inlet and outlet of the coreholder during the finial original crude oil reinjection after CO 2 flooding. 24

25 Immiscible and Miscible CO 2 Coreflood Tests (cont d) Immiscible and miscible secondary CO 2 flooding 100 Oil Recovery Factor (%) P=14.0 MPa P=12.0 MPa P=8.2 MPa P=7.4 MPa P=6.3 MPa P=5.4 MPa P=4.8 MPa Injected pore volume of CO 2 Oil recovery factor of CO 2 secondary flooding versus the injected P.V. of CO 2. 25

26 Immiscible and Miscible CO 2 Coreflood Tests (cont d) Immiscible and miscible secondary CO 2 flooding Asphaltene content of CO 2 -produced oil (wt.%) Oil effective permeability reduction Oil recovery factor Asphaltene content of produced oil Oil recovery factor (%) Oil effective permeability reduction (%) Injection pressure (MPa) Asphaltene content of CO 2 -produced oil, oil recovery factor, and oil effective permeability reduction in CO 2 secondary flooding at 2.0 P.V. of injected CO 2. 26

27 Immiscible and Miscible CO 2 Coreflood Tests (cont d) Three different miscible CO 2 flooding tests Oil recovery factor (%) CO 2 secondary flooding CO 2 dry flooding Secondary water flooding CO 2 tertiary flooding Secondary water flooding CO 2 tertiary flooding Injected pore volume of CO 2 or water Oil recovery factor of CO 2 and/or water flooding versus the injected P.V. of CO 2 or water at P=12.0 MPa. 27

28 Immiscible and Miscible CO 2 Coreflood Tests (cont d) Three different miscible CO 2 flooding tests Asphaltene content of CO 2 -produced oil (wt.%) Asphaltene content Recovery factor for CO 2 flooding Recovery factor for water flooding Oil effective permeability reduction D S T D S T D S T Test number Oil recovery factor (%) Oil effective permeability reduction (%) Asphaltene content of CO 2 -produced oil, oil recovery factor, and oil effective permeability reduction after CO 2 dry (D), secondary (S), and tertiary flooding (T) at 2.0 P.V. of injected CO 2. 28

29 CONCLUSIONS The molecular weight, density, aromaticity, and average number of o aliphatic carbon atoms per alkyl side chain attached to the aromatic atic rings for CO 2 -asphaltenes are lower than those of C 5 -asphaltenes. The onset pressure of asphaltene precipitation is lower if the asphaltene content of the crude oil is higher. The morphology of asphaltenes precipitated from a crude oil strongly depends on CO 2 EOR stage. The measured equilibrium IFT reduces almost linearly with the equilibrium pressure in three distinct pressure ranges for two light l crude oil CO 2 systems and in two different pressure ranges for a medium crude oil CO 2 system. The determined MMP is much higher if the crude oil is heavier. 29

30 CONCLUSIONS (cont d) In CO 2 secondary oil recovery process, the oil recovery factor and oil effective permeability reduction become higher at a higher pressure during the immiscible CO 2 flooding and they both reach an almost constant maximum value in the miscible CO 2 flooding. Among three different miscible CO 2 oil recovery processes, the oil effective permeability reduction of CO 2 tertiary oil recovery process achieves its largest value while the total oil recovery factor is the lowest. The secondary water flooding followed by the subsequent CO 2 tertiary flooding not only may be less effective than direct CO 2 secondary flooding but also may cause much more severe reservoir formation damage. 30

31 JOURNAL PAPERS ON CO 2 -EOR [1] Wang, X., Gu, Y., 2011, Characterization of Precipitated Asphaltenes and Deasphalted Oils of the Medium Crude oil CO 2 and Medium Crude Oil n-pentane Systems, Energy & Fuels, accepted on September 28, [2] Zhang, S., She, Y., Gu, Y., 2011, Evaluation of Polymers as Direct Thickeners for CO 2 Enhanced Oil Recovery, J. Chem. Eng. Data 56 (4), [3] Wang, X., Gu, Y., 2011, Oil Recovery and Permeability Reduction of A Tight Sandstone Reservoir in Immiscible and Miscible CO 2 Flooding Processes, Ind. Eng. Chem. Res. 50, [4] Wang, X., Zhang, S., Gu, Y., 2010, Four Important Onset Pressures for Mutual Interactions between Each of Three Crude Oils and CO 2, J. Chem. Eng. Data 55 (10), [5] Yang, D., Gu, Y., 2008, Determination of Diffusion Coefficients and Interface Mass-Transfer Coefficients of the Crude Oil CO 2 System by Analysis of the Dynamic and Equilibrium Interfacial Tensions, Ind. Eng. Chem. Res. 47, [6] Yang, D., Gu, Y., Tontiwachwuthikul, P., 2008, Wettability Determination of the Crude Oil-Reservoir Brine-Reservoir Rock System with Dissolution of CO 2 at High Pressures and Elevated Temperatures, Energy & Fuels 22, [7] Yang, D., Gu, Y., Tontiwachwuthikul, P., 2008, Wettability Determination of the Reservoir Brine-Reservoir Rock System with Dissolution of CO 2 at High Pressures and Elevated Temperatures, Energy & Fuels 22, [8] Nobakht, M., Moghadam, S., Gu, Y., 2008, Determination of CO 2 Minimum Miscibility Pressure from the Measured and Predicted Equilibrium Interfacial Tensions, Ind. Eng. Chem. Res. 47, [9] Nobakht, M., Moghadam, S., Gu, Y., 2008, Mutual Interactions between Crude Oil and CO 2 under Different Pressures, Fluid Phase Equilibria 265, [10] Nobakht, M., Moghadam, S., Gu, Y., 2007, Effects of Viscous and Capillary Forces on CO 2 Enhanced Oil Recovery under Reservoir Conditions, Energy & Fuels 21, [11] Tharanivasan, A. K., Yang, C., Gu, Y., 2006, Measurements of Molecular Diffusion Coefficients of Carbon Dioxide, Methane and Propane in Heavy Oil under Reservoir Conditions, Energy & Fuels 20, [12] Yang, D., Tontiwachwuthikul, P., Gu, Y., 2006, Dynamic Interfacial Tension Method for Measuring Gas Diffusion Coefficient and Interface Mass Transfer Coefficient in a Liquid, Ind. Eng. Chem. Res. 45, [13] Yang, D., Gu, Y., 2005, Interfacial Interactions between Crude Oil and CO 2 under Reservoir Conditions, Pet. Sci. Technol. 23, [14] Yang, D., Tontiwachwuthikul, P., Gu, Y., 2005, Interfacial Tensions of the Crude Oil + Reservoir Brine + CO 2 Systems at Pressures up to 31 MPa and Temperatures of 27 C and 58 C, J. Chem. Eng. Data 50 (4), [15] Yang, D., Tontiwachwuthikul, P., Gu, Y., 2005, Interfacial Interactions between Reservoir Brine and CO 2 at High Pressures and Elevated Temperatures, Energy & Fuels 19,

32 FUTURE WORK To perform all the static experiments or tests at the actual reservoir temperatures To conduct CO 2 -EOR coreflood tests at the actual reservoir temperatures in different immiscible and miscible CO 2 flooding processes with different CO 2 flooding timings after waterflooding To closely monitor and measure the produced gas composition, produced oil composition and its asphaltene content and composition during each CO 2 -EOR coreflood test 32

33 ACKNOWLEDGMENTS Petroleum Technology Research Centre (PTRC) Networks of Centres of Excellence (NCE) Secretariat Saskatchewan Ministry of Energy and Resources Natural Resources Canada (NRCan) Western Economic Diversification Husky Energy Canadian Natural Resources Limited BP Exploration (Alaska) Devon Energy

34 SPECIAL THANKS We want to express our special and sincere thanks to Ms. Xiaoqi (Vicky) Wang, who conducted most experimental studies given in this technical presentation during her Master s program with our research group at the University of Regina. Now Vicky is working as a Research Engineer in Saskatchewan Research Council (SRC).

35 WELCOME TO PTRC, CANADA 35