Thermo-hydro-mechanical and creep coupled analysis of interlayer effects on compressed air energy storage salt cavern stability and sealing integrity

Mudstone interlayers in natural salt formations significantly affect the (thermal-hydraulic-mechanical) THM coupled response of compressed air energy storage (CAES) caverns, yet existing studies lack comprehensive THM coupling analyses and systematic comparisons under varying interlayer quantities. Existing studies commonly adopt constant thermophysical property assumptions and rely on single-field or two-field coupling frameworks, leaving key coupling mechanisms inadequately captured. To address these limitations, the present work develops a fully coupled THM numerical model, incorporating surrounding rock creep behavior and temperature-pressure dependent thermophysical properties of compressed air. Interlayer quantity exerts limited short-term influence on gas temperature and pressure, with differences maintained within ±0.5 K and 0.5 MPa, respectively. However, these differences exhibit a cumulative increasing trend under long-term operation. The thermally affected zone expands following a power-law trend, reaching 12.28 m after 60 days. The pore pressure-affected zone in mudstone interlayers reached 15.97 m, approximately 7.5 times greater than the 2.11 m observed in salt rock, with this lithological disparity continuing to amplify over operational time due to the cumulative preferential seepage effect of mudstone interlayers. Interlayers significantly compromise sealing performance: cumulative leakage mass rises from 0.73 × 106 kg to 3.33 × 106 kg as interlayer quantity increases from 1 to 6, following a strong exponential correlation. Mudstone interlayers exhibit dual deformation effects: they restrain overall creep, reducing the volume loss ratio from 1.693% to 1.417%, while the peak equivalent creep strain increased substantially over the operational period, with interfacial strain concentration potentially triggering debonding or slippage under long-term cyclic loading.