## 1 Introduction
Some people [17] believe that there is a significant difference in the maximum hydrocarbon column height for cap rock sealing of oil and gas reservoirs with different lithological characteristics, with the closure hydrocarbon column height from high to low being gypsum-salt rock, mudstone, and carbonate rock. In continental basins, the displacement pressure of cap rock varies according to different lithological features, leading to differentiated cap rock sealing capabilities: gypsum-salt rock is the best, followed by mudstone, and carbonate rock having poor sealing performance. [PERSON] et al. [18] further analyzed the micro-morphology of  
Figure 1: The proportion of global primary energy consumption in 2020 and 2021.  
continental and marine mudstones through scanning electron microscopy and detected the relevant characteristic parameters of mudstones using X-ray diffraction behavior. They pointed out that the sealing efficiency of cap rock in underground storage in depleted gas reserves is mainly determined by pore diameter and lining. In the same period, [PERSON] et al. quantitatively evaluated the sealing performance of faults using the mudstone smearing factor algorithm based on the fault throw and juxtaposition relationship between the two rock strata on either side of the fault, combined with dynamic production data of gas reservoirs. This was used to discuss the feasibility of reconstructing underground storage in depleted gas reserves in Xinjiang. In the following year, [PERSON] et al. [19] conducted experiments to investigate the effect of saturated CO\({}_{2}\) solution on the trap dynamic sealing capacity of the underground storage in depleted gas reserves. The results showed that the permeability of the sealing system of underground gas storage composed of siltstone cap rock would be affected by the saturated CO\({}_{2}\) solution. When the fluid flows through the siltstone cap rock, it would directly increase the permeability by one order of magnitude, thereby sharply reducing the sealing performance of the underground gas storage sealing system. In addition to its own lithological characteristics, the mechanical characteristics of the cap rock in depleted gas reservoirs also affect the trap dynamic sealing capacity of underground gas storage. The main brittle-ductile evaluation indexes reflecting the mechanical characteristics of the cap rock are the Rock Brittleness Index (\(BRI\)), Overburden Confining Ratio (OCR), rock internal friction angle, and rock density. [PERSON] et al. [20] proposed the Brittleness Index in 1999 to quantitatively describe the rock's ability to undergo brittle fracturing:  
\[BRI=UCS/UCS_{NC} \tag{1}\]  
where \(UCS_{NC}\) is the uniaxial compressive strength of normally consolidated rock, \(UCS\) is the uniaxial compressive strength of over consolidated rock. Research has shown that the oil and gas reservoir cap rock are more prone to brittle fracture when the \(BRI\) exceeds 2. Additionally, [PERSON] et al. [21] evaluated mudstones in the North Sea basin and found that similar to the contribution of cap rock fractures, when the OCR exceeds 2.5, the rock will fracture, leading to natural gas leakage. The internal friction angle of rock and the intrinsic properties reflected by the specific surface area of the rock are both composite indicators of rock porosity, grain size, degree of compaction, and cementation. If the specific surface area is less than 300 m\({}^{2}\)/g, it indicates strong cementation and poor sealing of the cap rock in oil and gas reservoirs, making it prone to brittle fracture [16]. Similarly, rock density, greater than 2.1 g/m\({}^{3}\), also exhibits brittle rock characteristics, compromising the original sealing performance of the cap rock [17]. Building on this, [PERSON] et al.