Numerical Simulation of Flow Characteristics in CO2 Long-Term Storage in Bedded Salt Cavern

The salt layer, characterized by its low permeability and excellent damage self-healing properties, is an ideal geological body for CO2 geological storage. However, the relatively high permeability of mudstone interlayers may reduce the safety of CO2 long-term storage in bedded salt caverns. This study establishes a thermal–hydraulic–mechanical (THM) coupled physical and mathematical model for CO2 geological storage in the Huaian salt cavern, analyzes the factors affecting CO2 flow behavior, and proposes measures to enhance the safety of CO2 storage in salt caverns. The results indicate that the permeability of both salt layers and mudstone interlayers is influenced by stress-induced deformation within the salt cavern. From the salt cavern edge to the simulation boundary, the permeability and volume strain exhibit a trend of rapid decline, followed by a gradual increase, and an eventual stabilization or slight reduction. The seepage velocity, pore pressure, and flow distance of CO2 in the mudstone interlayer are significantly higher than those in the salt layer, leading to CO2 migration along the interfaces between the mudstone and salt layer. With the increase in storage time, the permeability of the mudstone interlayer gradually decreases, while the permeability of the salt layer shows a general tendency to increase. The elevated storage pressure reduces the permeability of the mudstone interlayer, while increasing the permeability of the salt layer, and enhances the seepage velocity in both the mudstone and salt layers. To enhance the safety of CO2 long-term storage in bedded salt caverns, it is recommended to minimize the presence of mudstone interlayers during site selection and cavern construction, optimize the storage pressure, and strengthen monitoring systems for potential CO2 leakage.