Dynamic Evaluation of Geological Trap Sealing for Depleted Reservoir Gas Storage Using Four-Dimensional Geomechanics

Underground gas storage converted from depleted oil and gas reservoirs requires reliable long-term sealing of caprocks, faults, and other geological barriers during cyclic injection and withdrawal. Conventional evaluations mainly focus on static geological parameters, whereas the effects of stress evolution during operation are often insufficiently addressed. In contrast, four-dimensional geomechanical simulations based on fluid–solid coupling can capture the dynamic evolution of geological sealing behavior under injection and withdrawal conditions. The review summarizes progress in heterogeneous geomechanical model construction, stress-field evolution under cyclic loading, dynamic sealing assessment of caprocks and faults, and determination of safe operating pressure limits. Geological sealing evaluation has evolved from a static assessment based on geological characteristics to a dynamic assessment controlled by mechanical criteria. Geostress inversion has developed from three-dimensional heterogeneous mechanical models to four-dimensional geomechanical dynamic coupling analyses that account for seepage, stress, temperature, and other factors. Safe pressure evaluation has also progressed from conventional gravity-driven storage construction to the assessment of critical pressure evolution during the safe operation stage. Existing studies indicate that heterogeneous parameter characterization, coupled flow-stress simulation, and dynamic pressure management strongly affect the reliability of sealing evaluation in reservoir-type UGS. The results further show that pressure history, stress redistribution, and creep effects should be considered together when assessing long-term storage safety. The engineering cases listed at the end of this paper verify some of the research findings. The results presented above are of great significance for the construction and safe operation of reservoir-type gas storage facilities.