Stability evaluation of underground gas storage salt caverns with micro-leakage interlayer in bedded rock salt of Jintan, China

Recent in situ pressure test indicates that there is a mudstone interlayer with high permeability in the open hole of the underground gas storage (UGS) salt caverns in Jintan, China. The interlayer is called the ``micro-leakage interlayer (MLI).'' MLI brings a great new challenge for UGSs construction and operation. The stability evaluation is the main research target of this paper. Laboratory tests have been carried out on samples collected from the target formation to determine the mechanical properties. A 3D geomechanical model of the two adjacent caverns with MLI is established based on the geological data and the laboratory test results. The minimum and maximum limit operating pressures are determined as 6 MPa and 18 MPa based on the numerical simulation results of six operating conditions. Two operating conditions (synchronous and asynchronous injection-production) are designed and discussed. The result shows that the MLI has little effect on the stability of the caverns and can be ignored. The stability under the two operating conditions is quite good, suggesting that asynchronous injection-production can be used in the actual operation. This makes the operation more flexible to meet unpredictable situations. The tightness analysis under the two operating conditions will be the subject of future investigations.