Softening model for failure analysis of insoluble interlayers during salt cavern leaching for natural gas storage

Abstract

Failure analyses of the insoluble interlayers are critical for a salt cavern leaching for natural gas storage. In this study, a series of brine immersion tests was carried out to investigate the softening laws of the mechanical characteristics of an argillaceous anhydrite interlayer. The test results show that brine immersion decreases the mechanical strength of the interlayer. A softening depth model of the interlayer specimens was developed based on the experimental results. This model was used to establish a mathematical model of the softening of an overhanging interlayer in a salt cavern during leaching. The softening model can predict the softening scope and the residual strength of the interlayer in different softening zones at different leaching times. The model was integrated with a numerical simulation to analyze the characteristics of failure of an overhanging interlayer. It was found that the interlayer tends to fail when the brine immersion time reaches a certain value in the simulation. Finally, the influence of environmental and artificial factors on the softening laws of the insoluble interlayer was discussed. It was found that the matrix structure and soluble components of the interlayer are two significant environmental factors and the brine immersion time is the key artificial factor. Therefore, the failure of an interlayer can be controlled by adjusting the brine immersion time during leaching a salt cavern.