Stability of the bedded key roof above abandoned horizontal salt cavern used for underground gas storage

A large number of salt caverns by solution mining are abandoned widely. After reasonable reformation, some of these caverns are expected to store energies, such as petroleum, natural gas, and compressed air energy. Different from other countries, salt formations of China are mainly bedded with lower thickness. In order to improve the mining efficiency of bedded salt formations, solution mining with double-well convection is widely adopted, which brings more horizontal caverns with larger dimensions and also larger roofs. When these horizontal caverns are transformed into underground energy storage, the layered roofs are easily suffered from unbalanced deformation and failure, and then become the channels of oil or gas leakage. Therefore, a series of theoretical analysis and numerical simulation were carried out to reveal the failure mechanism and stability of the bedded roof, and then some meaningful conclusions are acquired. Firstly, in the overlying strata, the argillaceous anhydrite layer is the key roof in the selection of the abandoned horizontal cavern for energy storage. Secondly, according to plate theory, the invalid of the bedded key roof needs to be treated into failure and instability respectively. Thirdly, the analysis on the vertical and horizontal stress in the key roof shows that it does experience a second type of instability. Finally, in order to maintain the stability of bedded key roof, the main influence factors require careful and comprehensive consideration, including the length of the long side, the thickness of the protective salt layer, and the internal pressure.