Numerical Investigation on the Effect of Different Interlayers Collapse Sediments on Safety of Gas Storage in Salt Cavern
Authors: Pan Peng-Zhi , Hussain Altaf 
Published: August 2024

ABSTRACT:
Salt caverns play an important part in large-scale energy storage, and their planning and economic evaluation have primary importance. Worldwide reserves of rock salt typically reside in graben or half-graben basins. However, different interlayers (IL) and tectonic faults (TF) usually form during the construction of salt caverns. There are significant issues for the safety of caverns with different interlayer composition utilized for underground gas storage (UGS). Therefore, it's essential to investigate the effect of different interlayers content collapse sediments in salt cavern underground storage structures. Using a self-developed numerical tool, i.e., CASRock, the effect of different interlayer contents on an adjacent cavern's safety are examined numerically. Numerical simulations indicate that caverns containing a higher interlayer content demonstrate superior stability performance compared to those with lower or no interlayer content. In the salt mine, the distance between the salt cavern and tectonic fault should be at least twice the maximum diameter of the cavern for safety considerations. The distance between the cavern roof and bottom should be greater than 10 m in rock salt formations. These results are providing enhanced guidance for the exploration and utilization of salt caverns in various related fields, facilitating their application in similar environment.

1. INTRODUCTION
Until now, salt caverns have been the only underground storage successfully used for pure hydrogen storage, since they are much safer and more cost-effective than other underground spaces. However, even a poor design or operated energy storage cavern can result in significant accidents (Liu et al., 2020). Therefore, the main factors in geomechanical design are safety and stability of rock salt caverns (Yang et al., 2015).
The proximity between the faults and the cavern plays a crucial part in ensuring the safety of the cavern and determining its allowable size. There is currently no approved understanding of the safety evaluation and design approach for caverns close to faults, which limits the construction of caverns in areas near faults in China. According to the Fig. 1 the distance between salt caverns and tectonic faults should be 120 m in the present study. Therefore, conducting research on the safety and failure mechanism of caverns near faults would be beneficial in expanding the size and applicability of salt cavern UGS, presenting promising prospects for application in China.
Previous studies investigated on the effect of cavern shape, depth, internal gas pressure, and operating condition. Nevertheless, the effects of various interlayer contents on UGS salt caverns stability have only been investigated in a small number of studies. In China, several types of nonsalt interlayers composed of a thin layer of salt with little halite are typical in the form of rocks for which thicknesses vary from dozens cm to more than one meter. For example, the Jintan salt mine has the low interlayer content (Liu et al., 2015).