Analytical assessment of CO2-storage efficiency and geomechanical-coupling behaviors using poromechanical experiments

Abstract

This paper presents an analytical assessment of the CO_2-storage efficiency and geomechanical responses to pore pressure buildup. The analytical assessment was based on the results of poromechanical experiments conducted on sandstone and shale samples from a prospective CO₂ geological-storage site off the southeastern coast of Korea. Pore compressibility, bulk compressibility, and specific storage coefficients were determined using a custom-designed hydraulic test system under varying pore and confining pressures. Static and dynamic rock properties were further characterized through uniaxial compression tests and ultrasonic velocity measurements. The data from these methods were integrated to evaluate CO₂-storage efficiency, rock deformability, and stress changes under different stress conditions. We found pronounced nonlinearity and hysteresis during loading and unloading cycles, owing predominantly to microcrack activity in sandstone and to hydration/dehydration effects in shale. Stress-dependent mechanical changes underscore the need to consider depth-specific conditions and cyclic loading during CO₂ injection. Under semi-closed boundary conditions, we estimated a storage-efficiency coefficient of 0.8–1.3 % and approximately 0.06 % vertical deformation for 10 MPa pore pressure buildup at 2,700 m depth. Consistent poromechanical coupling across methods insights for optimizing storage capacity and refining geomechanical models to ensure the long-term storage stability and effectiveness.