The SACROC Unit in the Permian Basin has been under carbon dioxide (CO2) injection for enhanced oil recovery (EOR) for almost forty years since CO2 injection commenced in 1972. The mature CO2 operations in the SACROC Unit make it an optimal site for studying CO2 sequestration in conjunction with EOR. A pilot demonstration project was performed in a five-spot pattern, beginning at the end of 2008. The objective of this study is to understand the capacity and flow patterns of the CO2 plume to determine sequestration potential in conventional oil reservoirs.

The pilot site locates in the Northern SACROC platform and was set up as a five-spot pattern consisting of 4 injectors and 1 center producer. Water and CO2 injection had occurred earlier in the SACROC Unit during reservoir development. The pilot testing started in 2008 and has been under CO2 injection since then. After thirteen months of CO2 injection, the production data from the pilot showed that the oil production rate of the producer (well 56-17) increased over tenfold during the first year of CO2 injection which demonstrated significant enhanced oil recovery by CO2 injection.

This paper describes how the injection process in the SACROC pilot was simulated using a compositional simulator, Computer Modeling Group’s GEM. A simulation model with 47,104 grids was developed with geophysical data characterized from 3D seismic surveys and well logs. The simulation area is 6640 ft * 6640 ft * 840 ft, consisting of five wells in the pilot site. History matching gas, oil, and water production for each well since first drilled was performed to verify the model. The EOR under three injection schemes was predicted. The CO2 storage capacity under residual and solubility trapping mechanisms during CO2 miscible displacement was simulated and analyzed. This study demonstrated CO2 sequestration in oil reservoirs to be a low-risk, promising method for mitigating CO2 discharge into the atmosphere.

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