CO2-based heavy oil recovery processes for post-CHOPS reservoirs

Cold Heavy Oil Production with Sand (CHOPS) is currently the process of choice for recovery from unconsolidated solution-gas rich heavy oil reservoirs. Compared to waterflood and thermal recovery processes, primary processes such as CHOPS have relatively low energy and emission intensities; in other words, they can be considered as relatively 'clean' fossil fuel energy recovery processes. However, with recovery factors between 5 and 15% at the end of its economic life, there is a search for follow-up processes that yield additional oil from these reservoirs with continued low energy and emission intensities. One option is CO2-based enhanced oil recovery (EOR) processes - CO2 can lower oil viscosity and if some fraction of the injected CO2 is sequestered in the reservoir, then the process can be considered a CO2 storage process in addition to an oil follow-up recovery process. Here, we evaluate the energy return and CO2 sequestered in cyclic CO2 and cyclic CO2-hot water injection processes in a post-CHOPS heavy oil field. The results reveal that overall recovery factors can be raised through appropriate design of the CO2 follow-up process. Cyclic CO2 injection achieves an incremental 2.4% recovery factor (over four years of operation) with high energy return ratio whereas CO2-hot water processes achieve higher recovery factors with lower energy return ratios. In these processes, the amount of CO2 that remains sequestered in the reservoir is small, typically less than 5%. Thus, these EOR processes are not strong candidates for CO2 sequestration.