## 3 Results
### FE-SEM Characteristics of Shale Reservoirs with Different Burial Depths  
In order to analyze the impact of the burial depth of shale reservoirs on the development of pores and micro-fractures, FE-SEM observations were conducted on shale cores from typical wells in the Zhaotong, Weiyuan, and Luzhou areas with different burial depths but from the same shale layer. The earliest descriptive pore classification scheme for shale reservoirs was proposed by [12]; this shale pore system is divided into three categories: organic matter (OM) pores, intraparticle (IntraP) pores, and interparticle (InterP) pores. The development degree of OM pores is influenced by the TOC content and OM type; the pores mainly develop in bitumen [53; 63]. Therefore, this study mainly observes the development characteristics of OM pores in bitumen. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample ID** & **Depth** & **TOC** & **Quartz** & **Feldspar** & **Carbonate** & **Clays** & **Pyrite** & **Porosity** & **P\({}_{\rm L}\)** & **V\({}_{\rm L}\)** \\  & **m** & **\%** & **vol, \%** & **vol, \%** & **vol, \%** & **vol, \%** & **vol, \%** & **\%** & **MPa** & **m\({}^{3}\)/t** \\ \hline YS203 & 1643.55 & 4.64 & 50.00 & 5.60 & 16.90 & 22.20 & 3.80 & 7.18 & 3.07 & 5.24 \\ YS138 & 1983.86 & 4.32 & 58.30 & 7.60 & 11.50 & 20.00 & 2.60 & 8.45 & 3.46 & 5.56 \\ YS137 & 1032.86 & 4.13 & 47.10 & 12.80 & 18.80 & 17.60 & 3.70 & 7.95 & 2.49 & 5.66 \\ W208 & 2746.78 & 4.81 & 44.10 & 14.10 & 13.90 & 23.20 & 4.70 & 6.28 & 5.08 & 3.67 \\ W203 & 3177.56 & 5.64 & 50.60 & 12.60 & 13.80 & 20.40 & 2.80 & 6.97 & 8.96 & 3.81 \\ W213 & 3746.19 & 4.37 & 40.19 & 10.26 & 27.00 & 20.96 & 1.59 & 5.84 & 5.98 & 2.88 \\ L206 & 4034.66 & 5.01 & 57.89 & 5.48 & 8.30 & 21.83 & 4.50 & 5.47 & 5.52 & 1.97 \\ L210 & 4274.95 & 4.63 & 46.89 & 6.09 & 14.78 & 27.70 & 4.54 & 5.25 & 5.64 & 2.29 \\ L214 & 4325.03 & 4.78 & 52.28 & 9.27 & 13.52 & 20.09 & 4.84 & 6.18 & 4.73 & 2.50 \\ Y2-7 & 4150.65 & 4.51 & 50.72 & 8.10 & 16.06 & 21.43 & 3.69 & 5.10 & 3.72 & 1.98 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: TOC content, mineral composition, porosity, and gas content parameters of the shale samples. The observation results show that the OM pores of the shale reservoir in the Zhaotong area (YS137 Well and YS138 Well), with a burial depth of less than 2000 m, exhibit a complex network structure with high connectivity, and the pore size of a single OM pore is basically less than 50 nm (Figure 4a,b,f,g). The OM pores of shale reservoirs in the Weiyuan area (W203 Well and W208 Well), with burial depths ranging from 2000 m to 3500 m, exhibit a phenomenon of \"polarization\". Both macropores and needle-shaped pores have developed, and the macropores mingle with each other, with an average pore size that is greater than 200 nm. The needle-shaped pores  
Figure 4: FE-SEM photos of OM pores in typical shale gas wells with different burial depths in the Zhaotong, Weiyuan, and Luzhou areas. (**a,b**) are OM pore photos of shale reservoirs in the Zhaotong area. (**f,g**) are local magnifications of OM pores in (**a,b**), respectively. The OM pores are in a network shape. (**c,d**) are OM pore photos of shale reservoirs in the Weiyuan area. (**h,i**) are local magnifications of OM pores in (**c,d**), respectively. The OM pores exhibit a phenomenon of “polarization”. (**e**) is OM pore photos of shale reservoirs in the Luzhou area. (**j**) is local magnification of OM pores in (**e**). The organic pores are circular in shape and relatively uniform in size. The red color in the photos of (**h–j**) represents the filling of OM pores, making it easy to observe small OM pores. Figure 3: Pressure-holding coring gas content results for high-quality shale in Well L214. are evenly distributed between the macropores, with pore sizes of only a few nanometers (Figure 4c,d,h,i).