Overview of physical-mechanical-chemical properties of bedded salt as underground energy storage (UES) in China

As the global demand for energy continues to rise, energy storage systems have emerged as a crucial component in attaining energy sustainability, which contributes to the balance between supply and demand and cost reduction. The Strategic Petroleum Reserve (SPR) constitutes a significant segment of China’s energy structure and is an essential part of the 13 th Five-Year Energy Plan of China. In the near future, a substantial amount of underground oil storage space will be established in deep salt mines in China. Owing to the low porosity (<1 %), low permeability (<10 −20 m 2 ), high ductility (30–40 %), excellent water-soluble mining properties, and good self-healing characteristics of salt rocks, underground salt caverns demonstrate superior performance in energy storage (natural gas, crude oil, etc.) compared to other forms including aboveground tanks, underground tunnels, aquifers, depleted reservoirs, and hard-rock caverns. Most notably, salt cavern storage is far more secure and cost-effective. In this contribution, therefore, we provide a review on the current status of underground energy storage (UES) in salt formations in China, based on the existing research in this field. In comparison with salt caverns in other countries, the characteristics and challenges of bedded salt caverns in China are illustrated. A systematic overview of the physical, mechanical, and chemical characteristics of layered salt is carried out, which provides a fundamental understanding of bedded salt and offers a reference for the further research and development of UES in China. Finally, we put forward a prospective future research direction on bedded salt for UES in China.