Gas-Control Effects of the Top and Bottom Plates and Geological Structural Conditions in the Xinan Coalfield.

In order to investigate the control mechanisms of the roof and floor strata, as well as geological structural conditions, on the occurrence and dissipation of gas, gas content measurements were conducted at five mining areas: Xinan, Xinyi, Yian, Mengjin, and Yunding within the Xinan coalfield. This study initiates an analysis of the mechanical properties, permeability, and geological conditions of the roof and floor strata of the Shanxi group no. II coal seam. By integrating field measurement data with numerical simulations, analysis of the controlling conditions for gas occurrence in the Xinan coalfield. The results indicate that the strength disparity within the composite reservoir of the no. II coal measure induces heterogeneous stress field distribution, significantly influencing methane adsorption-desorption dynamics. A distinctive "dissipation-priority" pattern emerges in the Yunding mining area due to synergistic effects between high-permeability roof strata and fault systems, contrasting with "preservation-dominant" modes observed in other areas where gas migration is inhibited by well-developed gas-resistant strata. The F fault and A anticline serve as primary control factors for gas occurrence, significantly contributing to the differentiation of gas content in adjacent mining areas, followed by the permeability conditions of the roof and floor strata. The central area of Yunding is identified as a gas accumulation zone, with a gradient dissipation rate toward the F fault ranging from 0.003096 to 0.002530 (m/t)/(Ma·10 m), and a gradient dissipation rate toward the A anticline between 0.002209 and 0.001824 (m/t)/(Ma·10 m). The 11th and 12th mining areas of Yunding are located in a gas weathering zone, while the 13th mining area partially lies within a methane zone. Focusing on the gas accumulation phenomenon in the 13th mining area is beneficial for preventing instability disasters in gas-bearing coal seams dominated by geostress.