## 4 Results and Discussion
### Description of 3D Stress Inversion before Reservoir Construction  
Based on the rock mechanical model of well points, the stress state of the measurement points can be determined, and combined with porosity, permeability data, water saturation, and other reservoir properties as constraints, a 3D stress model of the depleted gas reservoir is constructed. The stress state is inverted before reservoir construction. The 3D models of the Poisson's ratio and Young's modulus of the reservoir can be seen in Figure 7. The results show that the distribution of Young's modulus in 3D space is affected by \"phase control\" and porosity. In regions with higher porosity, Young's modulus is relatively smaller, which is consistent with the law of sedimentary sandstone. The correlation between the Poisson's ratio of the reservoir and conventional physical properties such as porosity is relatively poor, and its discreteness is relatively strong. In regions with a larger Young's modulus (greater rock strength), the Poisson's ratio is relatively smaller, indicating a weaker lateral expansion effect in harder rocks, consistent with the conclusions of the rock mechanical model at the well points. In addition, the cap rock and the reservoir of the underground storage in depleted gas reserves exhibit different geological characteristics. The 3D models of the Poisson's ratio and Young's modulus for the cap rock are shown in Figure 8. Compared to the reservoir, the spatial distribution of Young's modulus and [PERSON]'s ratio in the cap rock is relatively less dispersed in 3D space. However, the corresponding relationship between the [PERSON]'s ratio and Young's modulus in the cap rock is similar to the reservoir, in this area with greater rock mechanical strength, the Poisson's ratio is relatively smaller. Figure 7: A 3D model of [PERSON]’s ratio and [PERSON]’s modulus should be listed as: (**a**) [PERSON]’s ratio; (**b**) [PERSON]’s modulus. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \begin{tabular}{c} **Well** \\ **Number** \\ \end{tabular} & \begin{tabular}{c} **Stratification** \\ **Lithology** \\ \end{tabular} & \begin{tabular}{c} **Lithology** \\ **Minimum** \\ \end{tabular} & \
\begin{tabular}{c} **Static Elastic Modulus (GPa)** \\ **Maximum** \\ \end{tabular} &
\begin{tabular}{c} **Static Poisson’s Rate (Dimensionless)** \\ **Maximum** \\ \end{tabular} \\ \hline \multirow{2}{*}{SS203} & D2 & sandstone, & & & & & & \\  & silsttone, mudstone & & & & & & \\  & Yc3 & volcanic rock & 16.763 & 118.232 & 60.072 & 0.024 & 0.138 & 0.073 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._Based on the 3D stress inversion before the reservoir construction, the distribution pattern of the pre-construction stress field is obtained. The stress field has three principal stresses, with the vertical principal stress being the overburden pressure, and the other two horizontal principal stresses being the maximum and minimum horizontal principal stresses. From the analysis of the overall stress field, the overburden pressure is mainly determined by the rock density of the overburden strata and can be obtained through stress balance calculations. It will undergo systematic changes with depth. The distribution of overburden pressure before construction is shown in Figure 9, with the pressure distribution of the overburden in the cap rock ranging from 40 MPa to 76 MPa (Figure 10a), and in the reservoir layer ranging from 40 MPa to 88 MPa (Figure 10b). The distribution of maximum horizontal principal stress before construction is shown in Figure 11, with the distribution of maximum horizontal principal stress in the cap rock ranging from 48 MPa to 76 MPa (Figure 12a), and in the reservoir layer ranging from 50 MPa to 85 MPa (Figure 12b). Figure 8: A 3D model of Poisson’s ratio and Young’s modulus of caprock should be listed as: (a) Poisson’s ratio; (b) Young’s modulus. Figure 9: Distribution of the original vertical principal stress. Figure 11: The original maximum horizontal principal stress distribution.