Evaluation and improvement of CO2 assisted gravity drainage for enhanced oil production in China

In view of the diversity of petroleum reservoir types, most petroleum reservoirs have very strong heterogeneity in properties. For many water flooding reservoirs, with the continuous water injection process, the effect of enhancing oil recovery begins to deteriorate gradually, and a large amount of remaining oil mainly remains at the top of the reservoir formation, becoming as "attic oil". Under the "double carbon" target, in order to cope with the high demand for oil consumption in China, a new oil exploitation technology, CO2 assisted gravity drainage is explored in this study. Taking four cores with similar porosity and permeability as research objects, laboratory displacement experiments were carried out to verify the effectiveness of CO2 assisted gravity drainage in enhancing oil recovery through different CO2 injection methods and injection rates. Moreover, through the comparison of gas flooding recovery factors under different gas injection rates, it is found that the stable control of gas-oil interface is the key to the successful implementation of CO2 assisted gravity drainage. After that, based on references and numerical simulation, this paper analyzes the technical key points of the successful imple-mentation of this technology, proposes the method of introducing "surfactant + CO2" composite system to regulate the stability of gas-oil interface, and clearly points out the issues to be focused in future researches. The study can provide a useful reference for the field implementation of CO2 assisted gravity drainage, and then promote effective carbon utilization and oil production.