Feasibility analysis of using abandoned salt caverns for large-scale underground energy storage in China

Highlights: • A method is proposed for the evaluation of using an abandoned salt cavern for energy (natural gas) storage. • A feasibility analysis is given of China's first UGS (Underground Gas Storage) facility using an abandoned salt cavern. • Numerical modeling has been used to investigate mechanical safety of a gas pressurized cavern. • Chinese abandoned salt caverns show good feasibility of being converted to UGSs. • China's bedded rock salt can meet the requirements for UGS. - Abstract: Rock salt in China is primarily bedded salt, usually composed of many thin salt layers and interlayers (e.g. anhydrite, mudstone, and glauberite). Thus, the feasibility analysis of abandoned salt caverns located in salt beds to be used as Underground Gas Storage (UGS) facilities is full of challenges. In this paper, we introduce the feasibility analysis of China's first salt cavern gas storage facility using an abandoned salt cavern. The cavern is located in Jintan city, Jiangsu province, China. The mechanical properties and permeability of the bedded salts are obtained by experiments. Based on the results of the analyses, it appears to be quite feasible to convert the abandoned salt caverns of Jintan city to UGS facilities. The stability of the cavern is evaluated by the 3D geomechanical numerical simulations, and the operating parameters are proposed accordingly. Results indicate that the maximum volume shrinkage of the cavern is less than 25% and the maximum deformations are less than 2% of the caverns' maximum diameters after operating for 20 years. It is recommended that the weighted average internal gas pressure be maintained as 11 MPa to control the extent of the plastic zones to a safe level. Safety factors decrease with operating time, especially those of the interface between rock salt and mudstone layers decrease significantly. Effective strain is generally greater than 2%, and locally is greater than 3% after operating 20 years. The maximum pressure drop rate should be kept to less than 0.55 MPa/day. Based on above proposed parameters, China's first salt cavern gas storage facilities were completed, and gas was first injected, in 2007. To check the status of the caverns after operating for 6 years, the volumes of the caverns were measured in 2013 by Sonar under working conditions. Measurement results show that the cavern shapes did not change much, and that volume shrinkages were less than 2%. Comprehensive results show that the feasibility analysis method proposed in this paper is reliable