Integrated study on CO2 enhanced oil recovery and geological storage in tight oil reservoirs

Carbon utilization, and sequestration (CUS) in tight oil reservoirs stands as a pivotal strategy for enhancing oil recovery and mitigating CO2 emissions. Research on CUS mainly focuses on the calculation of overall displacement efficiency and the total sequestration amount. However, the primary control and sequestration mechanisms throughout the life cycle of CUS, as well as the contribution of each mechanism at different development stages and under various injection and production parameters, are not clear, which limits effective guidance for oilfield development. Therefore, this paper studies the entire life cycle of tight oil reservoirs, from water flooding to CO2 flooding and CO2 sequestration after reservoir abandonment. The contribution degree changes of dissolution, structural, residual gas and mineralized sequestration mechanisms during the whole life cycle are analyzed. The results show that the main sequestration mechanism during CO2 flooding stage and injection sequestration stage after shutting down production wells is structural sequestration, which accounts for 84.75%. In the 2000 years following the cessation of CO2 injection, the proportion of structural sequestration gradually decreases, with a cumulative decrease of 12.41%, and it is mainly converted to the other three sequestration modes, with the largest increase in mineralization sequestration, reaching 8.81%, mainly due to the reaction of dicalcium silicate with CO2 to produce more stable calcite. When the injection pressure was increased from 23 MPa to 44 MPa, the sequestration efficiency increased by 18.45%. An interesting finding is that the solubility of CO2 in water in the target reservoir reaches its lowest point at 80 degrees C, and both warming and cooling at this point are conducive to the dissolution and sequestration of CO2. The initial pH value of formation water mainly affects mineralization and sequestration. The rate of calcite production and the contribution of CO2 dissolution and sequestration are positively correlated with water saturation. The findings underscore the importance of understanding dynamic contributions of various sequestration mechanisms and optimizing conditions to enhance CO2 sequestration efficiency.