## 3 Materials and Methods  
### Static Triaxial Rock Mechanical Parameter Test  
The rock mechanical parameter is the basis for studying the characteristics of formation rocks and is one of the key data for evaluating the dynamic sealing of underground gas storage in depleted gas reservoirs. This mainly reflects the rock mechanics strength parameter (yield strength) and elastic parameter (elastic modulus, Poisson's ratio). Currently, rock mechanical tests are mainly divided into two methods: static and dynamic. In the static method, rock deformation is measured through static loading and confining pressure. The specific experimental steps are as follows:  
1. Preparation of rock core: For the Yingcheng formation and Denglouku formation, full-diameter rock core samples are extracted from 12 core wells according to different formations. Based on the rock core preparation device, each rock core sample is processed into three small cores with dimensions of 2.5 \(\times\) 5.0 cm. The two ends of the small rock core are ground flat using a grinding machine.  
Figure 5: Temperature and pressure system of formation should be listed as: (**a**) Typical well temperature depth relationship curve; (**b**) Typical well pressure depth relation curve.  
Installation of rock core: The processed small rock core samples are placed into the cavity of the triaxial mechanical testing instrument. Rubber rings are used to seal the boundary of the hydraulic module to prevent the fluid used for applying stress from permeating into the small rock core, thus affecting the accuracy of the triaxial rock mechanics test data. During the installation of the pressure plate and related components of the press, it is considered that although the ground flat surfaces of the small rock core have high-precision smoothness, there are still some micro-scale unevenness on the pressure plate surface in contact with the small rock core. Therefore, rubber pads are added to the contact surface between the pressure plate and the small rock core to balance the test error caused by the unevenness due to the inclined contact surface of the small rock core.
3. Confining pressure loading: After the installation of the rock core, three small rock core samples are subjected to three-directional confining pressures of 20 MPa, 30 MPa, and 40 MPa, respectively. The initial confining pressure is set to a low value with a pre-set loading rate of 0.05 MPa/s. Then, the pore pressure in the rock is increased by 10 MPa at a rate of 0.2 MPa/s and kept constant. Subsequently, the confining pressure is further increased until the effective confining pressure reaches the set value. The triaxial mechanical testing instrument automatically records the shear stress, normal stress, and strain of the rock on the loaded surface area in the tangential and normal directions. The stress state that leads the rock to reach the shear limit is also recorded. Finally, the static shear strength, static elastic modulus, and static Poisson's ratio are calculated using formulas. \[\begin{array}{l}\left|\tau_{f}\right|=\tau_{0}+\sigma_{n}\cdot tg\phi\\ E=\frac{F/A}{\Delta L/L}\\ \mu=\frac{\Delta d/d}{\Delta L/L}\end{array}\] (2) where \(\left|\tau_{f}\right|\) is the static shear strength of the rock, Pa; \(\tau_{0}\) is the tangential stress of the rock, Pa; \(\sigma_{n}\) is the normal stress of the rock, Pa; \(\phi\) is the internal friction angle of the rock; \(E\) is the static elastic modulus of the rock, Pa; \(F\) is the normal stress applied on the stressed area of the rock, N; \(A\) is the stressed area of the rock, m\({}^{2}\); \(\Delta L\) is the elastic deformation length in the normal direction after the deformation of the rock, m; \(L\) is the original length in the normal direction before the deformation of the rock, m; \(\mu\) is the static Poisson's ratio of the rock; \(\Delta d\) is the elastic deformation length in the normal direction after the lateral deformation of the rock, m; \(d\) is the original length in the normal direction before the lateral deformation of the rock, m.