Feasibility analysis on the utilization of TWH-caverns with sediment space for gas storage: A case study of Sanshui salt mine

Underground salt cavern (USC) has emerged as an optimal location for large-scale energy storage, encompassing oil, gas, hydrogen, carbon dioxide, and compressed air energy storage (CAES), owing to its inherent advantages of substantial capacity, stability, and hermeticity. However, most salt mines in China are characterized by a relatively thin salt layer thickness, a large number of interlayers and low salt layers grade. Consequently, a substantial proportion of the cavernous space resulting from water solution mining becomes progressively covered by insoluble sediment. Herein, the feasibility of gas storage in two butted-well horizontal (TWH) caverns with sediments, located within the Sanshui salt mine in Guangdong Province, China, is comprehensively analyzed through engineering investigation, physical model experimentation, numerical simulation, and theo-retical analysis. Firstly, a theoretical model was developed to calculate the volume of caverns based on salt grade (soluble content). Secondly, a joint physical model experiment and numerical simulation were conducted to obtain the most probable shape of the process for forming water-soluble caverns. Moreover, a novel technology was proposed to utilize sediment space for gas storage in TWH-caverns. Ultimately, the support pressure of surrounding rock was determined by using the passive earth pressure theory, and subsequently, an assessment of cavern stability was conducted. Here, the numerical simulation results demonstrated that in the absence of sediment space utilization, there was a limited capacity for gas storage, resulting in significant deformation of the surrounding rock and an increased level of roof instability. On the contrary, sediment can provide structural support to the surrounding rock, thus increasing its stability (the plastic zone expansion was reduced from 1600 % (0.3 sigma z), 1345 % (0.35 sigma z) and 1297 % (0.4 sigma z) to 109 %, 87 % and 78 %, respectively) and enhancing the capacity for gas storage. Accordingly, this study provides valuable guidance for the assessment of gas storage in low-grade salt sedimentary environments, as well as for the design of gas injection and brine discharge, and stability evaluations.