A comprehensive stability evaluation method of multiple salt caverns underground gas storage with interlayers

Underground gas storage (UGS) is usually constructed in a formation with complex geological characteristics, which makes the operation monitoring and safety management of this facility more difficult. This paper aims to develop a method for comprehensive stability evaluation of multiple salt caverns UGS with interlayers. An index system is established as the foundation of the analysis for evaluation, which includes six important factors: cavity shape, operation pressure, interlayer parameters, surrounding salt rock parameters, mechanical properties, and cavity spacing. The improved analytic hierarchy process (AHP) and entropy method are used to calculate the subjective and objective weights of each index respectively. Then the index weights are constructed in the form of combination weights. The fuzzy membership function method is applied to obtain a quantitative evaluation result. Based on the established evaluation model, the stability level of four multiple salt caverns UGSs with interlayer are successfully evaluated. The results show that the stable states of the four UGS facilities are all good. There is only a slight threat of instability in UGS2, which has the defects of too many interlayers, too large interlayer thickness and too small space between adjacent cavities.