Stability analysis of Pingdingshan pear-shaped multi-mudstone interbedded salt cavern gas storage

Abstract

In China, salt cavern gas storages are typically constructed in strata of complicated bedded salt rock, which are made up of numerous thin interlayers and salt rock that contains impurity. The long-term stability and safety assessment of underground caverns is crucial for the safe operation of gas storage in this type of complicated strata. In order to more accurately describe the long-term creep characteristics of salt rock and mudstone, the fractional derivative creep-damage (FDCD) constitutive model is used in this work. Earlier researches have also demonstrated the advantages of this model when it comes to long-term creep. Pingdingshan (PDS)'s shape and dimensions are developed in accordance with the formation conditions, and a three-dimensional geological model is built according to the designed gas storage. The long-term stability and safety of gas storage under various constant operating internal gas pressures (IGP), cyclic IGP, and gas extraction rates are investigated based on the comprehensive evaluation criteria including deformation, volume shrinkage rate, safety factor, and plastic zone. The results reveal that when the constant operating IGP is 13 MPa, and the cyclic IGP is 13–27 MPa PDS gas storage has good long-term stability and safety. While the plastic zone of mudstone interlayer is still presented at the top and bottom of the gas storage at IGP = 13–27 MPa, and the plastic zone is more pronounced at low constant and cyclic IGP levels. The safety factor of rock mass close to the sidewalls is always <1.5 throughout the long-term operation of gas storage, which makes it more vulnerable to dilatancy failure and requires attention. The deformation and volume shrinkage of gas storage are greatly impacted by the gas extraction rate, and the evolution characteristics of 4 indicators under various gas extraction rates are provided. This study provides a crucial reference for the design of gas storage in China's intricate salt rock regions with multiple interlayers in the PDS region.