Simulating the transport of brine in the strata of bedded salt cavern storage with a fluid

Simulating the transport of brine in the strata of bedded salt cavern storage with a fluid–solid coupling model

Chen, Xiangsheng / Li, Yinping / Ge, Xinbo / Shi, Xilin / Xue, Tianfu

Abstract The majority of salt mines in China are located in the strata of lacustrine deposition, which are interbedded structure consisting of rock salts and non-salt interlayers. In the solution mining stage, rock salts will be dissolved to form a cavity for storing natural gas or petroleum. But the non-salt interlayers will soften or even collapse under the immersion of brine (dissolved rock salt), some of which will sink to the cavern bottom to form insolubles, and the other part will become the surrounding rock of this cavity. The retention time of brine in a salt cavern depends on the cavern size and efficiency of solution mining, which is generally about three years. During this period, the brine can seep into the fractures and joints of interlayers, and then inevitably has physical and chemical interactions with the rock minerals (typically montmorillonite). To reveal the affected range and results of brine on the interlayers, this paper takes poro-elasticity theory into account convection–diffusion equation to form a new fluid–solid coupling equation, and then establishes an actual geomechanical simulation model for numerical solution. The calculation results show that the penetration of brine in interlayers is very obvious. The penetration range is 28.37 m within three years, which is about 5.6 times that of rock salt. As the penetration range increases, the brine pressure gradually decreases and eventually stabilizes. In addition, brine transport has complex coupling boundary conditions composed of concentration, pressure and geostress, which interact with each other. This research contents have important reference and guidance for the study on brine crystallization and halite self-healing, and can lay a foundation for the subsequent safe operation and tightness evaluation of salt cavern.

Highlights • A convection–diffusion equation under fluid–solid coupling is proposed. • The influence range of brine transport on interlayers and rock salts of salt cavern is obtained. • The sealing performance of interlayers controls the tightness of bedded salt cavern storage.