WAG-CO2 process : pore- and core-scale experiments

1. WAG-CO2 process : pore- and core-scale experiments M. Robin, V. Sygouni, J‑P Duquerroix S. Bekri, S. Gautier, O. Vizika and E. Fernandez Righi

2. Introduction • Among the parameters affecting the flow processes (Vizika et al, 1994, Avraam and Payatakes, 1999), the pore surface wettability is very important. • It depends both on the mineralogy and on the physicochemical properties of the used fluid system (Hirasaki 1991, Anderson 1986, Drummond and Israelashvilli, 2002). • It strongly affects the flow mechanisms and therefore the oil recovery (Cuiec, 1990, Jadhunandan and Morrow 1995, Schramm and Manhardt 1996, Bradford and Leij 1995, Odlenburg et al 2001). IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

3. Introduction • Both enhanced oil recovery and CO2 storage in reservoirs turned the Water Alternating Gas (WAG) injections to an interesting process (Christensen et al, 1998, Olsen et al, 1992, Akervoll et al, 2000). • In this paper we try to investigate the Water Alternating CO2 step by step starting from micromodel and core experimentsaiming to a future modeling of the hysteretic relative permeability curves. • Thus, gas injection experiments have been performed both in transparent micromodels and in a composite core. The visualization experiments in micromodels have been conducted under reservoir conditions using dead oil and reconstituted brine. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

4. Spreading coefficient (water wet system) • The fluid distribution in the pore network depends on the value of the spreading coefficient S: S > 0 : oil can easily flow within the porous medium S < 0 : oil can be trapped within the pore space (Vizika et al. 1994) IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

5. Experimental set-up (micromodels) • The confining cell containing the micromodel is designed to be able to work up to 200 bars; it is equipped with an integrated heating device allowing experiments up to 60°C. • Two sapphire windows, one located at the top and the other at the bottom of the confining cell, allow lighting and visualization. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

6. Glass micromodels • The micromodel consist of two glass plates; one supports the etching representing the “porous” network and the other the entrance and the exit of the fluids, the average size of the circular grains (circles) is 0.3 mm. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

7. Experimental conditions • Three wettability conditions were reproduced : clean state (WW), restored state (aged in oil for two months) and silanated state (OW). • Two different initial saturations were investigated prior to gas injection : Swi and Sor. • The fluids which were used were reconstituted brine, stock tank oil (dead oil) and CO2. • Visualization experiments have been performed under 2 reservoir conditions: • 60 bars and 55°C / CO2 under gaseous conditions (standard conditions) • 90 bars and 55°C (SC CO2) IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

8. Clean state (WW) : CO2 injection at Swi • Oil is brown, brine is white and CO2 is grey. • Brine is either present under the form of a film. surrounding the grains or under the form of pendular rings. This is a typical situation of a water-wet system. • Oil phase remains a continuous one and oil spreads on the brine. The spreading coefficient is positive. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

9. Clean state (WW) : CO2 injection at Sor • Both contact angles and fluid distribution show that this porous medium is water-wet. • Oil spreads on brine film and is found in between the brine and the gas phase. On the third picture (red circles), some gas blobs are observed in the middle of the pore bodies, surrounded by oil. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

10. Restored state : CO2 injection at Swi • This is a typical situation of a water-wet system. • These results are fairly similar to the ones obtained for the clean state. Aging has not significantly altered the wettability of the micromodel. • It can clearly be seen that the oil phase spreads on the brine; it can be deduced that the spreading coefficient is positive. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

11. Restored state : CO2 injection at Sor • Oil spreads on the brine film and is found in between the brine and the gas phase. Sometimes, it forms bubbles in the center of some pores. • On the second picture (red circles), some gas blobs are observed in the middle of the pore throats, surrounded by oil. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

12. Capillary pressure curves • In order to compare the micromodel wettability results with the wettability of a real core, the capillary pressure curves were measured by centrifuge for both cleaned and restored plugs. • These results are fairly similar to the ones obtained for the micromodels (cleaned and aged). • Aging has not significantly altered the wettability neither of the micromodel, nor of the plugs. The wettability after aging could be characterized as intermediate. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

13. Silanated state (OW) : CO2 injection at Swi • It can be seen that the medium is preferentially oil-wet. There is no contact between the brine and the glass. • The CO2 has flown through the oil phase. Oil is the only phase which is in contact with the pore walls. It seems that CO2 is always separated from the pore walls by an oil film (red circles). IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

14. Silanated state (OW) : CO2 injection at Sor • It can be seen on these pictures that the medium is oil-wet. Dark films of oil covers the grains and it is also under the form of pendular rings. • Brine is included within the oil phase (red circles). There is no contact between the brine phase and the CO2. They are always separated by an oil film. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

15. Silanated state (OW) brine and CO2 (90 bars 55°C : SC CO2) • Left picture represents a silanated (OW) porous medium, saturated with brine, after CO2 injection. It can be noticed that the pore walls wettability is intermediate. • On many occurrences (red circles) the observed contact angles tend to show that the system is even slightly preferentially CO2-wet. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

16. Silanated state (OW) Three phase (90 bars 55°C : SC CO2) • Silanated (OW) porous medium, saturated with brine, oil, and supercritical CO2. It can be seen on these pictures that the medium is oil-wet. • Dark films of oil covers the grains and it is also under the form of pendular rings. Brine is included within the oil phase (red circles). There is no contact between the brine phase and the CO2, they are always separated by an oil film. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

17. Remarks after micromodel experiments In water wet micro models: • the spreading coefficient is positive In oil wet models: • when CO2, brine and oil coexist, the CO2 is a non-wetting phase whereas the oil is the wetting phase. • when only two phases, CO2 and brine, are present, the CO2 may be the wetting phase. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

18. Experiments in a composite core IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

19. Experimental conditions Flow experiments performed in a composite under ambient conditions. • Experiments : • Gas injection at Swi • Brine injection at Swi • Fluids : • Gas : N2 • Oil : dodecane • Brine The two phase flow relative permeabilities were calculated with history matching using Pumaflow. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

20. Gas injection at Swi • The gas injection at the desired Swi was performed under constant pressure drop (0.5, 1.8 and 3.8 bars), and a backpressure of 5 bars was applied. • The oil and gas relative permeabilities (Kro and Krg), were calculated by history matching using the IFP's reservoir code "Pumaflow" (adapted to laboratory conditions). • Experimental and simulated results are in good agreement. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

21. Gas injection at Swi Average saturations in the composite before and after gas injection. Relative permeabilities calculated with Pumaflow IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

22. Gas injection at Swi Experimental and simulated oil and gas production IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

23. Gas injection at Swi Experimental and simulated gas saturation vs. time IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

24. Brine injection at Swi Average saturations in the composite before and after brine injection. Relative permeabilities calculated with Pumaflow Brine relative permeability is very low and rapidly increases after the breakthrough. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

25. Brine injection at Swi Experimental and simulated oil production and pressure drop The displacement seems to be frontal due to the late breakthrough after which the oil production is almost stabilized. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

26. Brine injection at Swi Experimental and simulated water saturation vs. time IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

27. Remarks after core flow experiments • During the N2 injection at Swi, fingering and early breakthrough occurred • The N2 injection is less efficient than the brine injection at Swi, where the displacement was frontal, and where, after the breakthrough, the oil recovery was almost stabilized. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

28. Conclusions • The aim of this study is to investigate the flow mechanisms during CO2 / N2 injection in porous media, for varying thermodynamic conditions and wettability, and the relative permeability curves hysteresis that occurs during WAG experiments. • Visualization experiments have been conducted in micromodels of different wettabilities. The aging process in dead oil did not strongly alter the wettability in both micromodels and cores. From the micromodel experiments it is shown that the fluid distribution varies with the surface wettability and the experimental conditions. The temperature and pressure conditions under which an experiment is performed determine the CO2 behavior which does not always play the role of a non-wetting phase. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia

29. Conclusions • Flow experiments have been also performed in a composite core, consisting of four plugs, in order to estimate the two-phase relative permeabilities which will be used in the future to model a WAG experiment. • The experiments showed that the N2 injection at Swi, where fingering and early breakthrough occurred, is less efficient than the brine injection at Swi, where the displacement was frontal, and where, after the breakthrough, the oil recovery was almost stabilized. IEA Collaborative Project on EOR - 30th Annual Workshop and Symposium - 21-23 September 2009, Canberra, Australia