A coupled thermo-hydro-mechanical-damage model for salt cavern gas storage under long-term injection-withdrawal operations

A coupled thermo-hydro-mechanical-damage (THMD) model was developed to characterize the long-term performance of gas storage in salt caverns. This model accounts for the thermodynamic behavior of natural gas, seepage dynamics, rock damage evolution, and the temperature dependence of the salt rock's elastic modulus. The model's reliability was validated against field tests and prior studies, demonstrating the necessity of accounting for surrounding rock damage. Using a 3D numerical model of the Jintan-X salt cavern, the stability and tightness under five gas injection-withdrawal frequencies were evaluated. After 50 years, the maximum gas temperature increased by 3.71 %, 4.15 %, 4.42 %, 5.38 %, and 6.65 %, while the peak pressure decreased by 3.48 %, 3.59 %, 5.64 %, 7.49 %, and 10.06 %, respectively. These results emphasize the need for dynamic adjustment of gas injection to maintain storage pressure. Higher injection-withdrawal frequencies resulted in larger temperature fluctuations and accelerated pressure decay. Accounting for damage mechanics further revealed reductions in gas temperature and pressure, especially under high-frequency injection-withdrawal cycling. The affected zone of temperature and pore pressure expanded over time, with temperature influence strongly frequency-dependent, while pore pressure range remained stable. Over long-term cycles, a damaged zone formed near the cavern wall, and its size increased with time and frequency.