## 5 Discussion  
### Effect of Organic Matter Characteristics on Shale Adsorption Capacity  
The abundance of organic matter is an important indicator for evaluating the pore development and the adsorption gas content in highly over-mature shale. Organic matter is the material basis for the formation of a nanoscale pore network. It possesses strong adsorption capacity, with its surface and internal pores being the main sites for gas adsorption [52]. From the correlation between V\({}_{\text{L}}\) and TOC of shale (Figure 12a), there is a significant positive correlation between V\({}_{\text{L}}\) and TOC, with a correlation coefficient of 0.883. Figure 11: The methane adsorption curves for the Taiyuan Formation shale in the SNCB. This indicates that the CH4 absolute adsorption volume increases with the increase of TOC content of shale, which is consistent with previous research findings [23; 48]. Meanwhile, through the analysis of the correlation between TOC and total PV as well as pore SSA in shale (Figure 12b,c), there is a positive correlation between TOC and SSA, with a correlation coefficient of 0.616. Additionally, TOC exhibits a weak positive correlation with total PV, with a correlation coefficient of 0.322. These findings indicate a significant coupling relationship among hydrocarbon generation, pore increase, and gas storage in shale. During the process of shale gas reservoirs, numerous nanoscale pores are formed within organic matter due to hydrocarbon generation and discharge. The higher the organic matter abundance in shale, the more developed the organic pores, and the increased pore SSA can provide more adsorption sites for CH4, thus effectively improving the shale adsorption capacity. Different types of organic matter possess varying chemical structures in shale, which impact the shale adsorption capacity. It can be observed from the experimental results of methane adsorption in shale with different types of organic matter that the organic matter exhibits the weakest adsorption capacity with type I kerogen (Figure 13a), while the organic matter has strong adsorption capacity with type II and III kerogen, with little difference between them. This is primarily attributed to the different macarels and microstructures of various types of organic matter. Compared to type I, the organic matter with type III kerogen has a higher vitrinite content and more aromatic structures, both of which exhibit a stronger affinity for CH4, therefore enhancing shale adsorption capacity [19]. Although the adsorption capacity of organic matter with type III kerogen is stronger, its hydrocarbon  
Figure 12: The relationship between pore structure parameters and \(\mathrm{V_{L}}\) and TOC for the Taiyuan Formation shale in the SNCB. (**a**) TOC and \(\mathrm{V_{L}}\); (**b**) TOC and SSA; (**c**) TOC and PV. generation capacity and potential for developing organic pores are poor, and almost no organic pores are developed during the thermal evolution process. In contrast, organic matter with type II kerogen has significant hydrocarbon generation potential and is easily able to develop organic pores [53]. Therefore, the adsorption capacity of organic matter with type II kerogen is slightly stronger than that of organic matter with type III kerogen in the study area. However, due to the high maturity of the Taiyuan Formation shale in the SNCB, which is in the stage of cracking and gas generation, the difference in organic matter type does not have a significant effect on shale adsorption capacity [19]. The organic maturity affects the development of organic pores in shale, therefore influencing the shale adsorption capacity. Most researchers believe that with the increase of organic maturity, the organic pores become more developed in shale, and the aromatization of organic matter gradually enhances, resulting in an enhancement of shale adsorption capacity [54,55]. Through the correlation between organic maturity and V\({}_{\text{L}}\), the absolute adsorption volume of shale decreases with the increase in organic maturity.