Optimization of CO2-SAG Flooding Techniques for Enhanced Oil Recovery: A CFD Simulation Approach

CO2 miscible flooding has been proven to effectively enhance displacement efficiency and contribute to Carbon Dioxide Enhanced Oil Recovery (CO2-EOR). Although the CO2-SAG (Soaking-Alternating-Gas) flooding method has demonstrated promising EOR capabilities experimentally, there remains significant potential for further optimization. This study conducts pore-scale simulations to compare the effects of continuous CO2 flooding, conventional CO2-SAG flooding, and two proposed improved approaches: Multi-Soaking CO2-SAG and Thickened CO2-SAG flooding. The VOF CFD model coupled with Fick's diffusion law is employed to simulate mass transfer and miscibility processes between CO2 and oil. The simulation results show that compared with continuous CO2 flooding, CO2-SAG flooding can make the remaining oil in the pore that was not displaced originally diffuse into the CO2 that has reached the affected area after sufficient mixing, and then be produced, significantly improving the recovery factor (9.1%). When implementing multi-cycle injection and soaking process, more remaining oil diffuses into the CO2 and is produced, further improving the recovery factor (3.0%). In Thickened CO2-SAG flooding, the displacement efficiency is improved due to the increased viscosity of CO2, which can occupy more pore throat space, allowing a higher proportion of remaining oil to diffuse out of the pores and be displaced. This effectively achieves an additional 3.4% oil recovery compared to conventional CO2-SAG flooding. These findings demonstrate that tailored soaking cycles and viscosity modification can optimize CO2-EOR, offering practical strategies for maximizing hydrocarbon recovery and carbon sequestration.