Hydro‐Mechanical‐Chemical Behavior of Sedimentary Rock During CO ₂ Injection

Abstract This study examines the effect of CO 2 treatment duration on the poroviscoelastic properties of sedimentary rock, including sandstone, limestone, and shale. A hydro‐mechanical‐chemical (HMC) coupling framework is employed to evaluate the time‐dependent response of fluid‐saturated rock subjected to CO 2 exposure. Laboratory experiments are performed on pristine specimens and those treated for 1–3 weeks, using a modified hydrostatic compression system. Carbonate mineral dissolution plays a key role in altering poroviscoelastic properties, especially in limestone and calcite‐bearing shales, leading to an increase in their porosity and Skempton's B coefficient, and a decrease in their bulk and solid moduli, as well as bulk viscosity. These changes enhance the time‐dependent deformation and influence the porosity evolution. The HMC model, calibrated with the experimental data, predicts CO 2 injection‐induced porosity changes by accounting for the competing processes of chemical dissolution and time‐dependent compaction. This study highlights the need to incorporate the coupled effects to accurately predict rock behavior during CO 2 storage and to support realistic assessments of long‐term reservoir and caprock performance.