The heterogeneous characteristic of coalbed gas occurrence and its geological control mechanism

Controlled by geological conditions, coalbed gas occurrence exhibits heterogeneity. Revealing its occurrence patterns and geological control mechanisms serves as a critical basis for implementing the "one mine, one policy; one mining face, one policy" gas control strategies in coal mines. Based on gas geological theories and methods, utilizing measured gas content data and relevant geological data, this study investigates the gas occurrence patterns and geological control mechanism in the area bounded by the F_17-1 and F₁₈ Faults within the No. 2-1 Coal Seam of Zhaogu No. 2 Mine. The results show that: affected by geological factors such as the thickness of the overlying bedrock, burial depth, faults, and synclines, the gas occurrence of the No. 2-1 Coal Seam in different ranges of the study area presents significant heterogeneity and differences in controlling factors. For the area with a burial depth of less than 790 m, the thin bedrock combined with shallow faults such as the F₃₀ Fault, its branch faults, and the FS₃ Fault is conducive to gas escape, which is the main reason for the overall low gas content in this region. Meanwhile, affected by burial depth, the gas content shows a trend of slow increase with the increase of burial depth. For the area with a burial depth greater than 790 m, the bedrock thickness is the dominant controlling factor for the overall distribution of gas occurrence. The bedrock thickness first increases and then decreases with the increase of burial depth, which is the main reason for the coal seam gas content first increasing rapidly and then decreasing as the burial depth increases. The pinch-out zone of the F_17-1 Fault and the S₄ Syncline area are local gas-enriched zones under the overall control of bedrock thickness. The gradual increase in coal seam gas content at the same depth level—progressing from the F₁₈ fault toward the F_17-1 fault—is primarily attributed to the gas dissipation effect of the F₁₈ fault.