## 5 Conclusions  
Considering that the underground storage in depleted gas reserves is based on the development of long-exploited depleted gas reservoirs, the original formation parameters from the gas reservoir development phase have become obsolete and cannot accurately describe the actual sealing and gas storage performance of cap rock. Therefore, based on dynamic development data of oil and gas reservoirs and the Study Area and Geological Features, combined with the results of static and dynamic rock mechanical parameter experiments, the rock mechanical attribute model for well points was constructed. Among these, there is a linear correlation between the dynamic and static data of the elastic modulus and Poisson's ratio, with the dynamic elastic modulus of the reservoir rock generally being greater than its static elastic modulus, and with significant differences in rock lateral expansion characteristics. For different lithological formations, the static elastic modulus of the volcanic rock in the Yingcheng formation is relatively consistent with that of the sandstone, siltstone, and mudstone of the Denglouku formation when the dynamic elastic modulus is 43.91 MPa or the Poisson's ratio is 0.1978. However, due to the differences in dynamic elastic modulus and dynamic Poisson ratio between the two lithologic strata, the static elastic modulus of the volcanic rock in the Yingcheng formation is significantly larger than that of the sandstone, siltstone, and mudstone of the Denglouku formation, the Yingcheng formation has better lithostatic mechanical strength and can serve as the primary gas storage space for the underground gas reservoir. Additionally, the 3D stress model of the current formation stress state was inverted to the stress state of the depleted gas reservoir before construction, describing the dynamic evolution process of the sealing and gas storage performance of the depleted cap rock and reservoir. The results show that the maximum horizontal principal stress in the cap and reservoir of the underground storage in depleted gas reserve before construction is distributed between 48-76 MPa and 50-85 MPa, respectively. Furthermore, the local stress of the volcanic rock reservoir in the Yingcheng formation is relatively high, while the stress of the adjacent grid decreases at the same depth, there is a significant \"stress arch\" effect, and the direction of the maximum horizontal principal stress in the cap rock and reservoir is nearly east-west. Furthermore, the sealing of the cap rock and faults of the underground storage in depleted gas reserves was assessed from both static and dynamic perspectives. The results indicate that the cap layer has a higher breakthrough pressure, and the faults of F2, F5, and F11 exhibit strong lateral and vertical sealing performance, demonstrating excellent static sealing performance. According to the dynamic stress field change process, the global cap rock shearing safety index is between 0.7 and 0.9, and the average fault slip index is only about 0.1, which indicates strong dynamic sealing performance and is suitable for construction as a gas storage, thereby realizing the dynamic evaluation of sealing and site optimization for underground gas storage in depleted gas reserve, providing guarantee for the safe and stable operation of its subsequent expansion, multi-cycle injection and production. X.Z. : investigation, resources, writing--original draft; J.H. : methodology, validation, writing--editing; C.W. : investigation, resources, writing--review; J.W. : methodology, investigation; H.X. : conceptualization, funding acquisition. All authors have read and agreed to the published version of the manuscript. This work presented in this paper was financially supported by the National Natural Science Foundation of China (Grant No. 52074090) and the Key Research & Development Program of Heilongjiang Province (Grant No. JD22A004). Not applicable. Data Availability Statement: Data are available from the corresponding author by request.