Utilization of produced gas of CO2 flooding to improve oil recovery

Large amounts of mixed gas containing CO2 and hydrocarbon would be produced during CO2 flooding. Injecting the produced gas back to reservoir can not only make full use of CO2, but also can reduce air contamination. Taking produced crude oil and gases with different CO2 concentration from Jilin oilfield as examples in this paper, the phase behavior and the physical properties of live oil-gas system were measured with a visible PVT apparatus. In terms of oil viscosity reduction and swelling, the gas with high CO2 concentration was found to be substantially effective. Furthermore, comparative slim tube tests of the oil recovery performance using the five kinds of gases under different operating pressure were conducted in one-dimensional model. Results indicate that displacement efficiency increases linearly with the increasing CO2 content in the recycle gas; displacement efficiency increases with operating pressure under immiscible conditions. Re-injecting produced gas with relative high CO2 concentration back to reservoir is a method both time-saving and cost-effective.