## 4 Results
### Pore Structure Characteristics  
According to the International Union of Pure and Applied Chemistry, the pores can be classified into three categories: macroposes (>50 nm), mesopores (2-50 nm), and micropores (<2 nm) [37; 38; 39]. The PV and SSA of different lithofacies are given in Table 3. The siliceous shale has the highest PV (2.37-3.3 cm\({}^{3}\)/100 g), and the highest SSA (33.94-48.56 m\({}^{2}\)/g), with average values of 2.88 cm\({}^{3}\)/100 g and 42.6 m\({}^{2}\)/g, respectively. The silicous-argillaceous mixed shale has an average PV of 2.07 cm\({}^{3}\)/100 g and an average SSA of 27.1 m\({}^{2}\)/g. The argillaceous shale has a PV in the range of 1.42-2.65 cm\({}^{3}\)/100 g (average = 1.86 cm\({}^{3}\)/100 g)  
Figure 6: SEM images showing organic matter pores in the Wufeng–Longmaxi shales. **(A,B)** Ovals-shaped organic pores, well DA, depth = 2247.09 m; **(C)** Round-shaped organic pores, well DB, depth = 3799.28 m; **(D,E)** Cellular organic pores, well DB, depth = 3809.24 m; **(F)** Organic pores developed between framboidal pyrite crystals, well DA, depth = 2247.09 m.  
and an SSA in the range of 19.82-50.06 m\({}^{2}\)/g (average = 28.63 m\({}^{2}\)/g). The PV and SSA in siliceous shales are higher than that of mixed and argillaceous shale.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Lithofacies**} & **Well Name** & **Depth (m)** & **Pore Volume (10\({}^{-2}\) cm\({}^{2}\)/g)** & **Surface Area (m\({}^{2}\)/g)** & \multicolumn{4}{c}{**Pore Volume (10\({}^{-2}\) cm\({}^{2}\)/g)**} & \multicolumn{4}{c}{**Surface Area (m\({}^{2}\)/g)**} \\ \cline{3-11}  & DA & 2204.43 & 1.71 & 23.79 & 0.52 & 0.94 & 0.25 & 17.16 & 6.52 & 0.11 \\ \cline{2-11}  & DA & 2220.08 & 1.72 & 26.07 & 0.63 & 0.84 & 0.25 & 20.33 & 5.63 & 0.11 \\ \cline{2-11}  & DA & 2237.06 & 1.42 & 19.82 & 0.46 & 0.75 & 0.21 & 14.93 & 4.8 & 0.09 \\ \cline{2-11}  & DB & 3743.3 & 1.77 & 25.87 & 0.6 & 0.93 & 0.24 & 19.15 & 6.62 & 0.1 \\ \cline{2-11}  & DB & 3754.04 & 1.84 & 25.07 & 0.56 & 0.97 & 0.31 & 18.53 & 6.41 & 0.13 \\ \cline{2-11}  & DB & 3776.11 & 1.91 & 29.7 & 0.7 & 0.99 & 0.22 & 22.55 & 7.06 & 0.09 \\ \cline{2-11}  & DB & 3817.27 & 2.65 & 50.06 & 1.19 & 1.26 & 0.2 & 39.64 & 10.34 & 0.08 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Pore volume, surface area of micropore, mesopore, and macropore for the Wüfeng–Longmaxi shales.  
Figure 7: SEM images showing inorganic pores in the Wüfeng–Longmaxi shales. (**A**) Intergranular pores, well DA, depth = 2247.09 m; (**B**) Intergranular pores between clay and calcite particles, and dissolved intraparticle pores within calcite, well DA, depth = 2262.2 m; (**C**) Intergranular pores and fractures, well DB, depth = 2267.7 m; (**D**) Intraparticle pores within calcite particle, well DA, depth = 2247.09 m; (**E**) Intraparticle pores within calcite particle, well DB, depth = 3799.28 m; (**F**) Intraparticle pores within dolomite particle, well DA, depth = 2267.7 m; (**G**) Micro-fracture pores developed between organic matter and minerals, well DB, depth = 3817.27 m; (**H**) Micro-fractures between clay platelets, well DB, depth = 3765.57 m; (**I**) Micro-fracture pores developed between organic matter and minerals, well DA, depth = 2269.74 m.  
The pore diameter range measured by CO\({}_{2}\) adsorption is typically 0.3-1.0 nm, and the pore diameter range measured by N\({}_{2}\) adsorption is typically 1.8-300 nm [30]. The pore size distribution calculated from N\({}_{2}\) and CO\({}_{2}\) adsorption isotherms suggests a dominant pore size of <100 nm for the WF-LMX shales regardless of shale lithofacies (Figure 8).