## 5 Discussion
### Relationship between the NMR Fractal Dimension and Mineral Composition  
The mineral composition of shale is a significant factor in determining the pore structure and connectivity. The investigation into the relationship between NMR fractal dimensions and the mineral composition of Funing Formation shale in the Gaoyou Depression revealed notable impacts of different mineral constituents. (Figure 10). The analysis reveals that \(\mathrm{D_{Min}}\) and \(\mathrm{D_{Max}}\) exhibit negative correlations with the quartz content and that \(\mathrm{D_{Max}}\) displays a particularly significant negative correlation with the feldspar content. The observed phenomenon can be explained by the relatively even surfaces of quartz and feldspar minerals, which lead to a reduction in the variability of pore structures. As a result, there is a decrease in the fractal dimensions. Moreover, quartz, having fewer pores and offering limited pore complexity, leads to a reduction in the fractal dimension \(\mathrm{D_{Min}}\). The correlation between the two NMR fractal dimensions of Funing Formation shale in the Gaoyou sag and the total amount of clay minerals may not be immediately evident [20; 21; 36; 37]. Nevertheless, prior research indicates a positive association between clay minerals and the presence of larger pores, which can have a substantial influence on surface roughness. This relationship was observed in a study conducted by [PERSON] et al. that investigated the pore characteristics of shale in the Sichuan Basin. Consequently, it is plausible that the fractal dimension of movable-fluid pores would exhibit a positive correlation with clay minerals [36]. Furthermore, [PERSON] conducted a study on the pore structure of continental shale within the Changing fault depression. The findings of this study revealed a positive association between the fractal dimension of bound-fluid pores and clay minerals [21]. However, the observed relationship between the NMR fractal dimension of Funing Formation shale and the overall quantity of clay minerals does not correspond with prior studies, indicating the limited presence of a robust correlation. In order to enhance comprehension of this distinction, the present study delves further into the impact of diverse clay minerals on the two fractal dimensions. It was found that NMR fractal dimensions showed different correlations with different clay minerals (Figure 11). \(\mathrm{D_{Min}}\) and \(\mathrm{D_{Max}}\) exhibited robust correlations with illite, while \(\mathrm{D_{Min}}\) demonstrated a strong positive association with the illite mixed layer. Previous research into the adsorption capacities of various clay minerals indicated that their order of adsorption capacity is as follows: montmorillonite, smectite, smectic mixed layer, kaolinite, chlorite, and illite [38]. The increase in illite content was  
Figure 10: Relationship between the shale NMR fractal dimension and mineral composition. found to reduce the number of bound-fluid pores, resulting in a negative correlation with \(\text{D}_{\text{Min}}\). Furthermore, the presence of illite in shale samples can lead to pore blockage as a result of its interaction with water. Moreover, a high concentration of illite in these samples also has an impact on the fractal dimension of large-pore movable-fluid pores. It is worth mentioning that illite-smectite is the predominant clay mineral in the shale samples obtained from the Funing Formation in the Gaoyou Depression. The mixed layer in question exhibits a greater specific surface area in comparison with chlorite, resulting in heightened mineral surface roughness and improved adsorption capacity [39]. These factors contribute to an increase in the fractal dimension of bound-fluid pores. The diverse sedimentary environments give rise to distinct impacts of different clay minerals on the processes of adsorption and on seepage pores, which align with previous research outcomes.