The Use of Abandoned Salt Caverns for Energy Storage and Environmental Protection: A Review, Current Status and Future Protections

The existence of a large number of abandoned salt caverns in China has posed a great threat to geological safety and environmental protection, and it also wasted enormous underground space resources. To address such problems, comprehensive utilization of these salt caverns has been proposed both currently and in the future, mainly consisting of energy storage and waste disposal. Regarding energy storage in abandoned salt caverns, the storage media, such as gas, oil, compressed air and hydrogen, have been introduced respectively in terms of the current development and future implementation, with site-selection criteria demonstrated in detail. The recommended burial depth of abandoned salt caverns for gas storage is 1000–1500 m, while it should be less than 1000 m for oil storage. Salt cavern compressed air storage has more advantages in construction and energy storage economics. Salt cavern hydrogen storage imposes stricter requirements on surrounding rock tightness, and its location should be near the hydrogen production facilities. The technical idea of storing ammonia in abandoned salt caverns (indirect hydrogen storage) has been proposed to enhance the energy storage density. For the disposal of wastes, including low-level nuclear waste and industrial waste, the applicable conditions, technical difficulties, and research prospects in this field have been reviewed. The disposal of nuclear waste in salt caverns is not currently recommended due to the complex damage mechanism of layered salt rock and the specific locations of salt mines in China. Industrial waste disposal is relatively mature internationally, but in China, policy and technical research require strengthening to promote its application. Furthermore, considering the recovery of salt mines and the development of salt industries, the cooperation between energy storage regions and salt mining regions has been discussed. The economic and environmental benefits of utilizing abandoned salt caverns have been demonstrated. This study provides a solution to handle the abandoned salt caverns in China and globally.