Effects of CO2–water–rock cycling cycles on sandstone pore structure

As global CO 2 levels increase, the storage of CO 2 in saline aquifers is considered a large-scale and cost-effective method for mitigating CO 2 emissions. To examine the impact of cyclic CO 2 injection on sandstone formations within various saline aquifers, five cyclic injections of differing durations were performed, and the effects of the frequency and duration of CO 2 injection cycles on sandstone pore structure were monitored using nuclear magnetic resonance. Additionally, ICP-OES was employed to assess changes in the total dissolved solids and metal ion concentrations in the saline water layer post-injection. The findings reveal that sandstone samples experience structural degradation as a result of cyclic injection. Initially, the proportion of macropores in sandstone samples increases with the number of injections but subsequently decreases. SO 4 2– ions exert a more significant influence on the sandstone pore structure compared to Cl − ions. The concentrations of Ca 2+ and Mg 2+ ions in the solution initially rise, followed by a subsequent decline. By integrating the principles of pore structure and considering the formation of crystals through the combination of metal cations and anions, the mechanism underlying the changes in sandstone pore structure due to cyclic injection is elucidated. This study explores the effects of CO 2 cyclic injection on reservoir sandstone and evaluates how different saline aquifer types affect pore structure deterioration. The research offers valuable reference points and a foundation for laboratory investigations of underground CO 2 storage in saline aquifers.