## 2 Materials and Methods
### Saltstone Stratigraphic Conditions and Cavity Building Plan
explored the underground salt cavern gas storage reservoir in Ye County, Pingdingshan, by using the Controlled Source Audio Geomagnetic Method (CSAMT) and the Geodetic Electric Field Petrographic Detection (CYT) method, and obtained the basic features such as the burial depth, dimensions, and spatial location of the underground caverns [32]. According to the summary of [PERSON], [PERSON] et al. 's study, the exploration results show that there are more cavities in the underground of the exploration area, with depths ranging from \(-1148.0\) to \(-1424.0\) m, and with moderate spacing between each other of about 90.0 to 450.0 m. The results are summarised in the following table. The cavity shows a narrow top and wide bottom, with a moderate volume of individual cavities, a range of cavity heights from  
Figure 1: Geographic location map of Ye County, Pingdingshan. 153.0 to 233.0 m, averaging about 199.4 m, and a cavity radius between 8.0 and 60.0 m. A schematic of the cavity profile is shown in Figure 2[33]. This paper presents the establishment of a single-cavity model of the salt cavern, created using Ansys 2020R1 and FLAC3D 6.00 software in accordance with the geological conditions observed in the salt cavern gas storage reservoir in Ye County, Pingdingshan. The study concentrated on the impact of varying numbers of mudstone interlayers on displacement changes at the top of the cavity and the volumetric shrinkage rate of the cavity, and presented a summary of the influencing laws. In regard to the long-term safety of salt cavern gas storage reservoirs, it is of paramount importance to select the optimal perimeter rock permeability and operating pressure to effectively prevent deformation resulting from the combined effects of creep and seepage, as well as potential incidents such as cavity instability and gas leakage. In order to facilitate the analysis, an ideal ellipsoidal cavity was constructed. In order to minimise the impact of boundary effects, the model length was set to be between six and eight times the diameter of the cavity. The specific model parameters are set as follows:  
All lines (NL1) have a cell boundary size (SIZE) of 2 and a segmentation ratio of 1 (SPACE). Number 1 (NL1) has a cell boundary size (SIZE) of 2 and is divided into 10 parts (NDIV) with a segmentation ratio of 5 (SPACE). Control over the cell shape: (1,3D) tetrahedral cell division mesh, (1,2D) triangular division; (0,2D) quadrilateral division, (0,3D) hexahedral division. Tetrahedral cell division mesh is selected. The grid type for mesh division: 0 free mesh division, 1 mapping mesh division, 2 first choice with mapping, if not, then free mesh division. Free mesh division was chosen. In this paper, an ellipsoidal cavity will be set up with a long axis of 200 m, a short axis of 100 m, and an aspect ratio of 2. The total length of the model is 1000 m, the width is 500 m, the thickness is 400 m, and the top of the cavity is 1100 m above the surface. Considering the geological data, the 14-20 salt group interlayers were studied and the thickness of the mudstone interlayer was set at 5 m. In order to deeply study the influence law of the number of mudstone interlayers on the long-term operation of the gas storage reservoir, two groups of control experiments will be set up: one group is 6 layers of mudstone interlayers, and the other group is 10 layers of mudstone interlayers. This design will help to understand the impact of the amount of mudstone entrapment on the long-term operation of a gas storage reservoir. The comparative analysis of the two sets of experiments can reveal more clearly the influence of different numbers of mudstone interlayers on the stability of gas storage reservoirs. Figure 2: Schematic of underground cavity profile [33]. As shown in Figure 3, the storage model schematic shows, in detail, the structure and location distribution of the storage reservoir. In this model, we choose the following key locations as observation points for displacement changes.