Stability evaluation of horizontal connected salt cavern compressed air energy storage in low-grade dipping salt layers

Compressed air energy storage (CAES) power plant is an important means of peak regulating and valley filling on the source side and load side of renewable energy, which plays an important role in ensuring the rapid development of renewable energy and the stability of power grid. Underground salt caverns are crucial sites for constructing CAES facilities. In recent years, China has planned over ten salt cavern-type CAES plants, with a cumulative installed capacity of 6000 MW; two of these have been successfully constructed and are operating smoothly. Layered salt rocks in China are often characterized by low grade, multiple interlayers, and formation dip angles, which significantly increase the difficulty of constructing storage facilities and operational safety risks. This study focuses on the horizontal connected salt cavern CAES in low-grade dipping salt layers, specifically aiming at the impact of formation dip angles on the safety of CAES salt caverns. The results indicate that the salt cavern volume shrinkage rate (VSR) and maximum displacement (Dis-Max) increase exponentially with depth, with a notable accelerating growth after exceeding 1500 m. An increase in formation dip angle exacerbates asymmetry in VSR and displacement in the lower cavern. For every 10° increase in dip angle at 2000 m depth, VSR and Dis-Max increase by 3.53 % and 489 mm, respectively. The sediment body exhibits a significant buffering effect on surrounding rock deformation, and its VSR is less affected by dip angle. The study proposes that for deep salt caverns (≥ 1500 m), controlling the dip angle (≤ 20°) should be prioritized, while for shallow caverns (< 1000 m), this can be relaxed to 30°. This research clarifies the influence of formation dip angle on the stability of CAES facilities, providing important references for the construction of CAES facilities in dipping salt layers widely distributed in China.