Research on the Site Renovation of Geological Compressed Gas Energy Storage by Sequestering CO2 in Depleted Oil and Gas Reservoirs

Abstract Geological compressed gas energy storage system achieves the large-scale energy storage, with fewer geographical limitations and lower costs. Continuous CO2 injection to form a cushion bubble is a key step in the site renovation of energy storage, achieving synergistic effects of CO2 sequestration and energy storage. However, the bubble shape maintenance and reservoir pressure losses in porous reservoirs under different well types are still unclear, thus it is necessary to conduct the in-depth analysis. Based on the numerical model of cushion gas renovation in depleted oil and gas reservoirs established in this study, visual distributions of bubble shapes in vertical and horizontal well systems were compared. Losses of reservoir pressure and CO2 saturation were analyzed. The results indicate that CO2 with a saturation of 0.4–0.5 around the well is the main source of energy storage. The average gas saturation of vertical systems is higher than that of horizontal systems, but the loss speed is faster. Horizontal well has a longer lifespan than vertical wells. For different well type systems, a regular replenishment of cushion gas is required. This study is expected to provide a reference for the promotion of compressed gas energy storage projects in depleted oil and gas reservoirs.