Research on shape optimization of salt cavern under different geological conditions

The reasonable design of cavity structure for different geological conditions is crucial for the long-term stability and safe operation of salt cavern gas storage. In China, complex salt strata with diverse geological features like thick or thin salt layers, shallow/medium/deep salt layers, and multi - interlayer salt layers pose challenges for designing suitable salt cavern shapes. Based on the typical storage-construction geological conditions of Yunying, Jintan, and Chuzhou salt mines in China, different three-dimensional geomechanical models were established, and a set of assessment index including displacement, plastic zone, volume shrinkage rate, safety factor, and equivalent strain were introduced to perform numerical simulation analysis of the stability of different salt cavity shapes under different geological conditions. The results indicate that: 1) Salt cavern stability declines with an increase in cavity diameter but improves with a higher cavity roof height; 2) Salt cavern volume increases with diameter expansion, whereas a higher cavern roof height results in a smaller overall volume. Morphological optimization necessitates an equilibrium between cavern stability and storage capacity; 3) Considering stability and maximum volume principle, for shallow-depth salt cavern gas storages (e.g., Yunying salt mine), salt cavern structure parameters of 80 m roof height and 90 m diameter are recommended; for medium-depth ones (e.g., Jintan salt mine), 80 m roof height and 80 m diameter are suggested; for deep-depth ones (e.g., Chuzhou salt mine), 60 m roof height and 80 m diameter are advised. This research can provide a reference for the shape design of underground salt cavern gas storage in other salt formation.