Effect of hard interlayer thickness on surrounding rock damage and tightness of hydrogen storage caverns in bedded salt formations — a study based on thermal-hydraulic-mechanical-damage (THM-D) coupling

Salt cavern hydrogen storage is considered a key technological pathway for establishing large-scale hydrogen energy reserves. To reveal the coupled influence mechanism of surrounding rock damage on the stability and gas tightness of hydrogen storage caverns in bedded salt formations, this study takes a salt mine in Jiangsu Province, China, as the background and develops a thermal-hydraulic-mechanical-damage (THM-D) coupled model considering the heterogeneity of the rock mass. In this model, a damage variable is introduced to dynamically capture the deterioration effects of surrounding rock damage on its mechanical and hydraulic properties. Based on this framework, the effects of hard interlayer thickness on surrounding rock damage and tightness in bedded salt hydrogen storage caverns are investigated. The results indicate that damage in the surrounding rock is mainly concentrated within the hard interlayers. Once damaged, the hard interlayer permeability increases exponentially, providing highly connected preferential seepage pathways for hydrogen migration. With increasing hard interlayer thickness, the displacement of the surrounding rock, the cavern shrinkage rate, and the damage extent within the hard interlayers gradually decrease. Moreover, the relationship between tightness and hard interlayer thickness is not linear. As the hard interlayer becomes thicker, tightness first decreases, then increases, and finally decreases again. These findings can provide valuable references for the construction and safety design of hydrogen storage caverns in bedded salt formations.