Large amounts of insoluble sediments formed in high impurity salt mines can inhibit the expansion of cavern bottom and can block or smash the debrining tubings during the gas injection and extraction process. However, these insoluble sediments are also conducive to the stability of salt cavern. Based on the force analysis of different sediment heights, a 3D geomechanical model is established to study the influence on the stability of salt cavern. The U-shaped horizontal salt cavern is used based on sonar scanning in the field and predicted cavern shape. Five evaluation indexes including deformation, dilatancy safety factor, plastic zone, volume shrinkage, and equivalent strain are used to analyze the stability of the cavern. Results show that the displacement, plastic zones, and equivalent strain gradually decrease with increase of sediment heights. The dilatancy safety factor and volume shrinkage increase with increase of sediment height. The equivalent strain mainly exceeds 3% around the horizontal part of the cavern, which should be taken seriously during the operation. The equivalent strain at the roof part of the vertical cavern is relatively low and does not exceed the upper interlayer position, which is conducive to the stability of the casing shoes. The sediments can significantly reduce the deformation of the cavern at the horizontal part, which is favorable to the stability of the cavern. This study can provide a reference for studying the stability effects of sediments on U-shaped horizontal salt cavern.

1. Introduction

Rock salt is recognized as an ideal medium for underground storage of natural gas, crude oil, and radioactive waste and CO2 disposal for its extremely low porosity and permeability (Liu et al., 2015). Underground gas storage (UGS) has a vast space to store natural gas compare to the facilities built on the ground surface. The consumption of natural gas increases dramatically during the cold reasons, which causes the gas supply to be a serious challenge. UGS can meet the needs of natural gas during peak consumption and store redundant natural gas during less consumption. Crude oil is a kind of strategic resource that is significantly important to a country's safety, and many countries have established underground strategic petroleum reserves (SPR) in rock salt formations (Zhang et al., 2017). Overall, underground salt caverns have become a vital position to ensure national energy security.

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