Enrichment Law and Controlling Factors of CBM in the Xishanyao Formation of the Hedong Mining Area, Urumqi

The enrichment laws and key controlling factors of coalbed methane (CBM) in the Xishanyao Formation of the Hedong mining area remain unclear, restricting exploration progress. Based on well data and experimental analyses, this study investigates CBM enrichment characteristics and geological controls using genetic identification diagrams. Results demonstrate that CBM exhibits a “high in northwest and low in southeast” planar distribution. Vertically, CBM content is extremely low above 360 m due to weathering oxidation and burnt zone effects, increases within the 360–950 m interval (peaking at 750–950 m), and declines from 950 to 1200 m because of limited gas contribution. Genetic analysis indicates predominantly primary biogenic gas, with a minor component of early thermogenic gas. Enrichment is controlled by structure and hydrogeology: the medium-depth range (358–936 m) on the northern syncline limb and western part of the northern monoclinal zone forms a high-efficiency enrichment zone due to compressive stress from reverse faults and high mineralization groundwater (TDS > 8000 mg/L). While the southern limb, characterized by high-angle tensile fractures and active groundwater runoff, suffers gas loss and generally low gas content (<3.5 m3/t). This study clarifies CBM enrichment laws and enrichment mechanisms, supporting exploration of low-rank CBM in the Hedong mining area.