In China, gas storage in deep salt caverns faces challenges due to high in situ stresses, elevated geothermal temperatures, and the presence of interbedded salt-mudstone formations. These factors lead to heterogeneous deformation and stress concentration, which adversely affect the stability and sealing capacity of salt caverns. To address these issues, this study systematically investigates the differences in the mechanical responses of a dual-cavern system located in a representative deep salt district under synchronous and asynchronous injection-production processes. The impacts of key operating parameters on the long-term deformation evolution of salt caverns under thermo-mechanical coupling are examined, and the effectiveness of the asynchronous operation strategy in optimizing the cavern stability is quantitatively evaluated. The results demonstrate that asynchronous operation significantly enhances the stability of the inter-cavern pillar. Specifically, this strategy disrupts the connection between zones with high stress-to-strength ratios, thereby reducing the risk of coupled failure between the two salt caverns. Furthermore, this strategy improves the distribution of the dilatancy safety factor of the surrounding rocks. Asynchronous operation also performs well in mitigating long-term deformation of the salt caverns, resulting in a lower risk of unilateral pillar instability, reduced cavern roof subsidence, and diminished volume shrinkage. Notably, asynchronous operation can effectively suppress cavern deformation under high-frequency injection-production cycles. Increasing the operating rate and decreasing the minimum pressure result in decelerating and accelerating deformation trends, respectively. Sensitivity analysis identifies the minimum pressure as the primary factor directly controlling cavern deformation, while operating frequency benefits most from the adoption of an asynchronous operation strategy. Overall, the findings of this study are expected to advance the construction and operational optimization of deep salt caverns for gas storage in China.

A thorough understanding of the microscopic flow process in porous and fractured media is significant for oil and gas development, geothermal energy extraction and subsurface CO₂ storage etc. In CO₂ geological sequestration, the CO₂ is often injected at the supercritical state (scCO₂), which will displace the connate fluids in the pore spaces during the drainage process. However, when CO₂ injection stops, the connate brine or water flows back to displace the scCO₂. Therefore, the configuration of migration paths in a specific reservoir plays a significant role in affecting the connectivity and storage efficiency of scCO₂. In this paper, the two-phase (scCO₂ and water) boundary has been defined using the phase field method, and the COMSOL Multiphysics simulator is applied to study the migration of scCO₂ in porous/fractured media at the pore scale. The geological conditions of Shiqianfeng formation in the CO₂ capture and storage pilot site of the Ordos Basin in China is selected as the engineering background. Before using the actual microscopic geometry based on thin-section of Shiqianfeng sandstone, we get the general understanding on scCO₂ migration in fractured porous media that has the highly simplified configuration with circular particles, considering the impacts of wettability, geometry of formation mineral grains, interfacial tension, injection rates, and fracture geometry. Results show that the CO₂ preferential flow occurs at locations with high CO₂ flow rates and high CO₂ pore pressure. The preferential flow of scCO₂ occurs adjacent to the wall of grains while minimal or little flow takes place through the interior between the grains, considering the grains with irregular shapes. The interfacial tension of porous media plays a significant role in controlling the spatial distribution of the scCO₂. A much lower interfacial tension results in a much thinner scCO₂ flow band with a much higher saturation. The geometry of fractures in porous media increases the complexity of the scCO₂ flow paths at the pore scale.