Fracture-Influenced Seepage Behavior and Storage Capacity of Compressed Air Energy Storage in Closed Mine Roadways under Cyclic Operation

Repurposing roadways in closed coal mines for compressed air energy storage (CAES) offers a promising route for resource recycling and large-scale energy storage. Frequent rapid charging–discharging triggers cyclic temperature–pressure fluctuations in surrounding rock and causes air-leakage risks for underground CAES facilities. This work investigates air-leakage behaviors and thermo-hydro-mechanical (THM) coupling responses of CAES in closed mine roadways. Based on mass-energy conservation, a THM coupled numerical framework integrated with a fracture-growth permeability model is established to describe gas migration, pore-pressure evolution and convective heat transfer. Series of numerical simulations are carried out to quantify the effects of cavern initial temperature, gas-injection temperature, injection rate, initial surrounding-rock damage degree, operation cycles and injected-gas type on system performance. The results indicate that cavern pressure rises nearly linearly during charging and declines steadily during discharging. Compression induces rapid gas-temperature growth, which later decreases via heat exchange with surrounding rock. According to single-factor sensitivity analysis, the injected gas type (relative contribution of 32.92%), initial rock-mass damage (30.01%), and number of cycles (29.78%) are the three dominant factors governing gas-leakage magnitude. Reservoir temperature, gas injection rate and injected-gas temperature exhibit relatively limited influences under the investigated conditions. After 100 continuous charging–discharging cycles, the cavern gas density decreases by approximately 12%. Under identical conditions, hydrogen yields larger leakage mass flux than air and carbon dioxide, whereas carbon dioxide obtains higher equilibrium pressure. This study reveals the coupling mechanism between air leakage and thermodynamic responses for roadway-based CAES and advances multiphysics coupling theories for mine-related energy storage. The obtained results offer theoretical insights into the leakage-thermodynamic coupling mechanism of abandoned-roadway CAES.