Comprehensive risk evaluation of underground energy storage caverns in bedded rock salt

Abstract

Rock salt is accepted as an ideal medium for underground energy storage due to its low permeability, favorable creep and damage recovery properties. Different from the “pure” salt domes in Europe and other western countries, bedded salt deposits with multiple thin interlayers buried at shallow depth are widespread in China. The complex geological conditions increase the risk possibility of underground energy storage disaster. The comprehensive risk evaluation is of great importance for underground energy storage in bedded rock salt. According to the statistical results of catastrophic accidents in global rock salt mining, the risk factors leading to the oil or gas leakage, surface subsidence and the cavern group failure were analyzed and identified with the fault tree method. On this basis, the performance functions of surrounding rock slabbing, cavern tightness, excessive volume convergence and surface subsidence were proposed. The comprehensive risk probability evaluation methodology and risk classification standard were established for underground bedded rock salt storage cavern. By application of the comprehensive risk assessment system, the risk failure probability for Jintan bedded salt cavern group was calculated and the integrated risk level of which was evaluated. The appropriate operating pressure range (3–22 MPa) determined through theoretical calculation for Jintan bedded salt cavern group at a lower risk level coincides with that obtained from the conducted three-dimensional geomechanical model tests, verifying the validity of the proposed comprehensive risk evaluation method.