Characteristics of gangues in deep No.8 coal seam and their relationship with production capacity in Daning–Jixian block, Ordos Basin

The deep No.8 coal seam in Daning–Jixian block in the eastern Ordos Basin demonstrates promising exploration potential. However, there is unclear understanding of the distribution characteristics and influence mechanisms on production capacity of the well-developed coal gangues. The high-precision identification and characterization of gangues in No.8 coal seam have been conducted by full-diameter spiral CT scanning for core section from eight wells in the study area, as well as coal rock laboratory data such as proximate analysis, pore structure, and mineral composition. Furthermore, a comprehensive evaluation has been performed on the development characteristics of gangues and their relationship with gas content, reservoir sensitivity, and production capacity. The results indicate that gangues in No.8 coal seam are extensively distributed in Daning–Jixian block, with a thickness proportion of approximately 25.16% in individual wells, a density of about 2.3 layers/m, a single-layer thickness of 0.02–1.57 m (generally<1 m), and the cumulative thickness of 0.20–2.66 m. The gangues are featured by low carbon content, low proportion of micropores, and poor adsorption performance, resulting in weaker gas generation and adsorption capacity compared to coal seams. The average clay mineral content in gangues is 61.61%, dominated by illite/montmorillonite mixed-layer minerals, kaolinite, and illite, which are prone to water and velocity sensitivity, adversely affecting the stability and effectiveness of post-fracturing flow pathways. It shows distinctly negative correlation between gangue content, average thickness, maximum single-layer thickness, and daily gas production. The study concludes that the gangues not only reduce the overall organic content of coal seams but also enhance reservoir heterogeneity and sensitivity, ultimately reducing well production capacity. These findings provide a scientific basis for optimizing hydraulic fracturing design and rational drainage strategy of deep coalbed methane in Daning–Jixian block.