Experimental Analysis and Numerical Simulation of the Stability of Geological Storage of CO(2): A Case Study of Transforming a Depleted Gas Reservoir into a Carbon Sink Carrier

[Image: see text] Geological storage of CO(2) is one of the most economical, feasible, and effective measures to slow down global warming. In this study, a combined long core model was designed to study the seepage characteristics of supercritical CO(2) displacement. Moreover, the stability of permanent storage of cushion gas layers formed by supercritical CO(2) injection has been systematically studied. The research results showed that in the supercritical temperature and pressure range of CO(2), the front edge of CO(2) displacement can form a relatively stable seepage zone. Supercritical CO(2) displacement can achieve a high gas-storage rate and stable CO(2) storage. At the same time, the recovery rate of remaining natural gas has been significantly improved. As the injection pressure increased, supercritical CO(2) inhibited the reverse diffusion of natural gas molecules. Therefore, the breakthrough of the supercritical CO(2) displacement front under a high pressure lagged behind. However, due to the increase in the density difference of gas molecules, the forward diffusion of supercritical CO(2) has been enhanced. Temperature will not significantly affect the displacement and storage effects of supercritical CO(2) in gas reservoirs. The increase in injection pressure and reasonable control of the injection rate can delay the breakthrough of supercritical CO(2) displacement. These measures are conducive to the stable storage of CO(2) and the improvement of remaining natural gas recovery. The implementation of CO(2) geological storage is suitable for the later stage of gas reservoir depletion development. The high-density gravitational heterogeneity of supercritical CO(2) enables the injected CO(2) to form a stable high-density cushion gas layer in the gas reservoir, which can achieve stable CO(2) storage for more than 100 years.