Co-optimization of oil recovery and CO2 storage for cyclic CO2 flooding in ultralow permeability reservoirs

Cyclic CO2 flooding is an efficient method to enhance oil recovery in ultralow permeability reservoirs. As the demand for low carbon economy development, co-optimization of CO2 storage and utilization should be considered. In this research, initially a comprehensive optimization method was proposed, which co-optimize oil recovery and CO2 storage by different weighting factors. Then, a series of core flooding experiments were performed using the core samples collected from Changqing oilfield, which is a ultralow permeability reservoir with heterogeneity and micro-cracks, CO2 injection parameters of slug size and Injection-Soaking Time Ratio (ISR) were optimized. The results revealed that the optimal injection parameters changed for different optimization objectives. In the case where equal important to oil recovery and CO2 storage were considered, the optimum CO2 injection parameters in the ultralow permeability reservoirs were 0.03PV for slug size and 1: 1 for ISR. Comparing the method of oil recovery optimization (omega(1) = 1) to co-optimization of oil recovery and CO2 storage (omega(1) = omega(2) = 0.5), oil recovery was reduced by 8.93%, CO2 storage was significantly increased by 25.85%. The results provide an insight into parameter optimization of CO2 enhanced oil recovery design.