Leakage Risk Analysis of Underground Gas Storage Salt Caverns with Micro-leakage Interlayer in Bedded Rock Salt of Jiangsu, China

An in-situ pressure test indicates that there is a mudstone interlayer with a higher permeability than that of other interlayers in the open hole section of the UGS salt caverns in Jiangsu (China). This interlayer is denominated as “Micro-Leakage Interlayer (MLI)”. To analyze the leakage risk brought by the MLI, a 3D geomechanical model of two adjacent caverns has been established. The results show that: (1) asynchronous injection–production method does not have an adverse effect on the tightness of the caverns, (2) under synchronous injection–production condition: the gas leakage rate through MLI (4.27%) accounts for more than 50% of the total; the seepage distance in MLI is about 225 m, (3) the pore pressure inside MLI will dissipate completely within 10 years after the caverns are abandoned, while for other interlayers, the time will be more than 30 years, (4) the MLI has a seriously negative influence on the tightness of the UGS salt caverns. This work analyzes the cause of the MLI leakage and the leakage risk. To ensure that there is no adverse interlayer in the cavern and open hole section, in the future cavern construction, the detailed engineering geology investigation of the target formations and the detailed tests of the core within the target depths should be carried out.