Spatial Variations in Methane Content and Their Main Controlling Factors of the Deep‐Buried Coalbed in the Nalinhe–Hengshan Area, Ordos Basin

Deep‐buried coalbed methane (DCBM) exhibits significant exploration potential, though with notable spatial variations in gas content. The primary geological factors controlling the differential enrichment of DCBM and their respective influences remain unclear, as their distributions are usually controlled by many factors at the same time. Based on well data and core analysis data, this study focuses on the Coal Seam No. 8 in the Nalinhe–Hengshan areas of the Ordos Basin. Through systematic characterization of coal lithology, quality, reservoir properties, and gas‐bearing characteristics, combined with quantitative Pearson correlation analysis, it was determined that ash content is the main factors controlling the spatial variations of the total gas content. The lower ash content, the higher total gas content of the Coal Seam No. 8. It is worth to note that total gas content of the Coal Seam No. 8 in the Nalinhe area (average 11.4 m³/t) is far less than the Hengshan area (average 26.3 m³/t). The Nalinhe area, adjacent to the subaqueous distributary channel mouth bars in the delta front, experienced strong terrigenous clastic input, resulting in a higher proportion of detrital minerals in the coal and consequently higher ash content (average 22.5%). In contrast, the Hengshan area is situated in a lagoon farther from the subaqueous distributary channel mouth bars, with weaker terrigenous input and lower ash content (average 12.8%). Additionally, coal porosity shows a significant positive correlation with free gas content, governing the differences in free gas content between the Nalinhe (average 2.6 m³/t) and the Hengshan (average 10.7 m³/t) areas. The relatively higher ash content in the Nalinhe coal leads to the lower organic maceral content compared to the Hengshan. Well‐developed plant cell cavities and fractures in the vitrinite and inertinite contribute to higher porosity in the Hengshan coal. Additionally, the local presence of sandstone in the overlying strata of Coal Seam No. 8 in the Nalinhe area facilitated the escape of free gas into overlying sandstone, further reducing free gas retention. This study improves current knowledge about the enrichment mechanisms of the DCBM.