Enhanced Oil Recovery and CO2 Storage Performance in Continental Shale Oil Reservoirs Using CO2 Pre-Injection Fracturing

CO2 pre-injection fracturing is a promising technique for the recovery of continental shale oil. It has multiple advantages, such as oil recovery enhancement, CO2 geological storage and water consumption reduction. Compared with conventional CO2 huff and puff and flooding, CO2 pre-injection features higher injection rates and pressures, leading to EOR and improved CO2 storage performance. Combining physical experiments and numerical simulation, this research systematically investigated the EOR and storage performance of CO2 pre-injection in continental shale reservoirs. The results showed that CO2 pre-injection greatly improved the oil recovery; after seven cycles of soaking, the average oil recovery factor was 39.27%, representing a relative increase of 31.6% compared with that of the conventional CO2 huff and puff. With the increasing pressure, the CO2 solubility grew in both the oil and water, and so did the CO2 adsorption in shale. Numerical simulation indicated that the average CO2 storage ratio of the production stage was 76.46%, which validated the effectiveness of CO2 pre-injection in terms of CO2 geological storage.