Research on the control factors of gas content differences in the main mining seam of Baode Coal Mine

The gas content of the No.11 coal seam mainly mined at the lower part of Baode Coal Mine is significantly lower than that of the No.8 coal seam mainly mined at the upper part. The cause of this abnormal phenomenon remains unclear. This study systematically compares the coal-rock characteristics （including metamorphism degree, microstructure composition, ash content and moisture content）, coal seam thickness, burial depth, sedimentary environment, geological structure and reservoir pressure of No.8 and No. 11 coal seams through technical means such as borehole coring, engineering well testing, laboratory testing and system analysis. The research results show that the core controlling factor for the difference in gas content between the two sets of coal seams is the reservoir pressure. The average reservoir pressure of No.8 coal seam reaches 2.28 MPa, which is significantly higher than 1.30 MPa of No.11 coal seam, with a relative increase of 75%. Further analysis confirmed that the main controlling factor of the reservoir pressure difference is the runoff effect of the Ordovician limestone water: No.11 coal seam, due to its proximity to the Ordovician limestone water aquifer, is affected by groundwater runoff, resulting in a decrease in reservoir pressure and further exacerbating gas escape. This study, through multi-parameter collaborative comparison, identifies the main controlling factors for the difference in gas content between the upper and lower main mining coal seams in Baode Coal Mine, reveals the key controlling role of hydrogeological conditions on the occurrence of coal seam gas, and provides a theoretical basis for gas prevention and control in high-gas mines.