Characteristics of CO2–Formation Water–Rock Reaction and Simulation of CO2 Burial Efficiency in Tight Sandstone Reservoirs

To clarify the characteristics of CO2–formation water–rock reactions in tight sandstones and their effects on CO2-enhanced oil recovery (EOR) efficiency and storage efficiency, this study takes the tight oil reservoirs of the Changqing Jiyuan Oilfield as the research object. A variety of experimental techniques, including ICP-OES elemental analysis, powder X-ray diffraction, and scanning electron microscopy, were employed to systematically investigate the mechanisms and main influencing factors of water–rock reactions during CO2 geological storage. The study focused on analyzing the roles of mineral composition, reservoir pore structure, and formation water chemistry in the reaction process. It explored the potential impacts of reaction products on reservoir properties. Furthermore, based on the experimental results, a coupled reservoir numerical simulation of CO2 injection for EOR and storage was conducted to comprehensively evaluate the influence of mineralization processes on CO2 EOR performance and long-term storage efficiency. Results show that the tight sandstone reservoirs in Jiyuan Oilfield are mainly composed of calcite, quartz, and feldspar. The dominant water–rock reactions during CO2 formation–water interactions are calcite dissolution and feldspar dissolution. Among these, calcite dissolution is considered the controlling reaction due to its significant effect on the chemical composition of formation water, and the temporal variation in other elements shows a clear correlation with the calcite dissolution process. Further analysis reveals that water–rock reactions lead to permeability reduction in natural fractures near injection wells, thereby effectively improving CO2 EOR efficiency, enhancing sweep volume, and increasing reservoir recovery. At the end of the EOR stage, mineralized CO2 storage accounts for only 0.53% of the total stored CO2. However, with the extension of time, mineralized storage gradually increases, reaching a substantial 31.08% after 500 years. The study also reveals the effects of reservoir temperature, pressure, and formation water salinity on mineralization rates, emphasizing the importance of mineral trapping for long-term CO2 storage. These findings provide a theoretical basis and practical guidance for the joint optimization of CO2 EOR and geological sequestration. Future research may further focus on the dynamic evolution of water–rock reactions under different geological conditions to enhance the applicability and economic viability of CO2 storage technologies.