## 5 Discussion
### Effect of Mineral Composition on Shale Adsorption Capacity  
The inorganic minerals in shale mainly include clay minerals and brittle minerals. Different inorganic minerals have distinct differences in crystal structure and physical and chemical properties, which result in varying SSA of these minerals. Therefore, the variation in mineral composition and content leads to differences in the pore structure of shale and its impact on methane adsorption capacity [57]. The mineral composition of the Taiyuan Formation shale in the SNCB mainly consists of quartz and clay minerals, accounting for over 70%. Only sample Z-20 has a predominant mineral composition of carbonate minerals, which accounts for 57.7%. Therefore, quartz and clay minerals may have the most significant impact on shale pore structure and methane adsorption capacity. By analyzing the correlation between clay mineral content and pore SSA, it can be concluded that there is a positive correlation between the clay mineral content and pore SSA of shale, indicating that the clay minerals in Taiyuan Formation shale have a certain influence on its pore SSA (Figure 15a). Since there is a positive correlation between clay mineral content and pore SSA of shale, which further affects the methane adsorption capacity of clay minerals, it can be concluded that there is a significant positive correlation between clay mineral content and V\({}_{\rm L}\). The correlation coefficient is 0.50 (Figure 15b). This also indicates that the clay mineral content is the main factor determining the adsorption capacity of marine-continental transitional shale. The strong plasticity of clay minerals is the main reason. As their content increases, the compaction of the formation causes a closer arrangement of clay minerals, which promotes the deformation of large pores in shale. This leads to a decrease in pore size and an increase in the number of micropores and mesopores in shale, gradually increasing the pore SSA and improving methane adsorption capacity. However, due to the stronger hydrophilicity of clay minerals, the correlation between V\({}_{\rm L}\) and clay minerals is significantly weaker than that with organic matter. The main components of clay minerals in the Taiyuan Formation shale include I/S mixed layer, illite, and kaolinite. By analyzing the correlation between clay mineral composition and SSA and V\({}_{\rm L}\), it can be concluded (Figure 15a,b) that the kaolinite content in shale is positively correlated with SSA and V\({}_{\rm L}\), with correlation coefficients of 0.33 and 0.67, respectively. The illite content has a weak negative correlation with SSA and V\({}_{\rm L}\). The content of the I/S mixed layer shows no correlation with SSA but exhibits a weak negative correlation with V\({}_{\rm L}\). It indicates that an increase in the kaolinite content leads  
Figure 14: The relationship between pore structure parameters and V\({}_{\rm L}\) for the Taiyuan Formation shale in the SNCB. (**a**) SSA and V\({}_{\rm L}\); (**b**) PV and V\({}_{\rm L}\). to a corresponding increase in the SSA of shale pore, and due to its weak hydrophilicity, kaolinite enhances the methane adsorption capacity of shale. However, an increase in illite content may lead to an increase in the large pore content of shale, which reduces the SSA of shale pore. Additionally, both illite and I/S mixed layers have strong hydrophilic abilities. Water molecules will adsorb onto their surfaces, occupying adsorption sites and blocking the pore throat, therefore reducing the methane adsorption capacity of shale [58]. Therefore, the influence of clay mineral composition on shale adsorption capacity is more complex. Brittle minerals in shale primarily consist of quartz, feldspar, and carbonate minerals. By analyzing the correlation between brittle minerals and SSA and \(\mathrm{V_{L}}\), it can be concluded that there is a weak negative correlation between carbonate mineral content in shale and SSA and \(\mathrm{V_{L}}\) (Figure 15c,d).