Gas leakage assessment method of underground gas storage in multi-interlayer salt mine

In China, the gas storage in underground salt cavern is normally built in the lacustrine sedimentary salt rock, which is rich in muddy interlayers. Since the permeability and porosity of muddy interlayers are higher than those of salt rock, the sealing of the gas storage is determined by the permeability of muddy interlayers. In this study, a new theoretical model is established for the seepage analysis of bedded salt cavern gas storage. This model is based on the sedimentary characteristics of mudstone interlayer, which is horizontally distributed. Natural gas leakage is also calculated by using the porosity-permeability testing data and the actual operation parameters of the mudstone in a gas reservoir. According to the above results, this study analyzes the influencing factors and change regularities of gas leakage and seepage range. Furthermore, an applicability evaluation is given by considering several key parameters in siting and designing the gas storage reservoir, such as safe distance from salt cavern to salt mine boundary or faults, safe salt pillar width of adjacent storage and some others design indexes of rock salt gas storage. The analytical results show that pore pressure in the muddy interlayer firstly decreases sharply along the radial direction, and then tends to be stable. Gas seepage range and leakage at a certain time are determined by the permeability parameters of the interlayer, permeability media and the initial pore pressure together. The influencing range of seepage gradually increases with time elapsing, and eventually becomes stable as well. Hence, this study can provide theoretical and technical support for the location, design and sealing evaluation of multi-interlayers salt cavern gas storage.