Experimental Study of Gas Thermodynamic Responses and Sealing Plug Deterioration Characteristics in Compressed Air Energy Storage Caverns

During the frequent charging, discharging, and storage processes of underground compressed air energy storage systems, the damage and degradation of sealing plugs directly affect the long-term stability of gas storage caverns. Using a self-developed cyclic charging–storage–discharging–restorage gas disturbance rock testing system, this study conducted cyclic gas disturbance tests on sealing plug specimens at different storage pressures, followed by post-disturbance uniaxial compression tests, to investigate the thermodynamic response during cyclic disturbances and elucidate the mechanical property degradation mechanism of sealing plug specimens after cyclic disturbances. The results show that, during a single cycle, the gas temperature exhibits staged responses characterized by compression heating, cooling during high-pressure storage, decompression cooling, and temperature recovery during low-pressure storage. As the storage pressure increases, the heating rate increases from 0.005 to 0.016 °C/s, while the cooling rate increases from 0.023 to 0.055 °C/s. During cyclic charging–storage–discharging–restorage processes, the gas temperature exhibits an overall logarithmic growth trend comprising three stages, namely a rapid increase, a slow increase, and stabilization, with the degree of heat accumulation increasing progressively with storage pressure. Cyclic alternating loading by high-pressure gas aggravates internal specimen damage. With increasing storage pressure, the peak strength of the specimens after cyclic disturbances decreases by 8.14%, 8.99%, 11.58%, and 15.05%, respectively, while the elastic modulus decreases by 2.12%, 6.45%, 8.88%, and 13.49%, respectively. Acoustic emission activity during failure becomes more pronounced, and deformation localization intensifies. With increasing storage pressure, the macroscopic failure mode gradually changes from localized cracking to multiple-crack coalescence and block fragmentation, while the increase in average fracture-surface porosity rises from 7.29% to 37.89%. These results are important for assessing the stability of sealing plugs in underground CAES caverns.