## 3 Results
To illustrate, the settlement value at the upper limit of the reservoir increased from 0.019 m to 0.089 m over the course of 30 years, while the maximum uplift value at the lower limit rose from 0.011 m to 0.055 m over the same period. By observing the vertical displacement cloud diagram of the surrounding rock of the gas storage reservoir in Figure 4, it is found that with the increase in time, the maximum settlement value of the surrounding rock at the top of the reservoir is always larger than the maximum uplift value at the bottom of the reservoir, e.g., the maximum settlement value of the top of the single-cavity reservoir with eight layers of mudstone interlayers after 30 years of operation is 0.089 m, and the maximum uplift value of the bottom of the reservoir is 0.055 m. The asymmetry in the vertical displacement of the gas reservoir envelope is due to the different effects of creep action on the top and bottom of the reservoir. During the operation of a gas storage reservoir, there may be differences in the stresses and temperatures to which the top and bottom are subjected, which could result in disparate creep effects between the two. The upper portion of the reservoir may experience greater stress levels than the lower portion. Furthermore, given that temperature typically increases gradually with depth, the temperature at the bottom may be higher than at the top, resulting in disparate creep effects. Thus, the fact that the maximum settlement value at the top of the gas storage enclosure is consistently greater than the maximum bulge value at the bottom over time is due to the different effects of creep on the top and bottom of the storage reservoir. The horizontal displacement cloud map of the surrounding rock after 30 years of operation was obtained by numerical simulations for the vertical single-cavity salt rock reservoir with eight layers of mudstone interlayers, as illustrated in Figure 5. The remaining models exhibited comparable patterns. Figure 5 illustrates that the horizontal displacement of the surrounding rock in the single-cavity vertical gas storage reservoir is influenced by the surrounding pressure, with a tendency for expansion into the cavity. This suggests that the surrounding rock has undergone horizontal deformation in the direction of inward contraction, which has resulted in a reduction in the effective volume of the gas storage reservoir. At the same time, the horizontal displacement of the enclosing rock shows a clear symmetry with respect to the vertical displacement of the top and bottom of the enclosing rock. This means that the maximum value of the displacement change towards the interior of the cavity at the horizontal ends is approximately equal. For example, the horizontal displacement values at the horizontal ends of the reservoir in year 30 are 0.1149 m and 0.1227 m. This symmetry may be attributed to the deformation of the surrounding rocks occurring horizontally under the influence of similar geologic stresses and confining pressures, which results in the deformation of the surrounding rocks occurring horizontally showing a similar tendency at the two ends. A summary the variation of perimeter rock displacement with time for a single-cavity vertical gas storage reservoir is shown in the Figure 6. Overall, these observations help to understand the deformation characteristics of the gas storage enclosure rock when subjected to subsurface pressure, which is of great engineering significance for the design and management of gas storage reservoirs. Figure 5: Horizontal displacement of the surrounding rock of a single-cavity vertical gas storage reservoir with time: (**a**) One year; (**b**) Five years; (**c**) Ten years; (**d**) Twenty years; (**e**) Thirty years. Figure 6: Plot of perimeter rock displacement versus time for a single-cavity vertical gas reservoir.