Geomechanical integrity assessment of geological storage for carbon dioxide based on dynamic fluid–solid coupling

The sealing integrity of geological bodies is fundamental to the safe geological storage of CO₂ in oil and gas reservoirs. Conventional assessments of caprock and fault integrity mainly emphasize lithology, pore structure, and fault gouge characteristics, while often overlooking stress changes induced by reservoir injection and production. This study establishes criteria for caprock and fault failure and instability and conducts four-dimensional geomechanical simulations based on dynamic fluid-solid coupling. The evolution of geological integrity coefficients under injection and production conditions is obtained. The results indicate that during CO₂-based enhanced oil recovery and storage, pore pressure gradually increases while effective stress within the formation decreases. Under the combined influence of evolving pore pressure and changes in in situ stress, the sealing behavior of the caprock exhibits complex dynamics. Fault shear stress exhibits only minor variation, and the faults retain strong sealing performance throughout the simulation period. Both the caprock and fault geomechanical integrity coefficients remain greater than 1, suggesting a low leakage risk under the evaluated operating conditions. These results demonstrate that incorporating in situ stress evolution under dynamic injection-production conditions can significantly improve the assessment of mechanical integrity and sealing performance of geological bodies. This study provides a useful basis for the safe and efficient implementation of CO₂ storage in oil and gas reservoirs.