Tectonic control law and zoning division of coal seam gas occurrence in Sichuan Province

Understanding the coal seam gas occurrence law is the premise and foundation of gas disaster prevention and production planning. The tectonic control law and zoning division of gas occurrence in Sichuan Province have been discussed, based on the gradual tectonic control theory for gas occurrence, combined with coal mine gas-geology data and a geological survey in Sichuan Province. The obtained results indicate that the generation, migration, and preservation of gas are controlled by the formation and development, cracking, subduction collision, and intracontinental orogeny of the upper Yangtze block. The gas occurrence and distribution characteristics in Sichuan Province are significant. Gas occurrence of Late Permian coal seams is significantly higher than that of Late Triassic coal seams, as 85.7% of the outburst mines in the Sichuan Province are distributed into the Late Permian coal seams. The Late Permian coal seams in the Xuyong-Junlian superimposed fold belt and Huayingshan detachment fold belt are high gas occurrence zones. These zones had been under strong tectonic compression for several years, thereby resulting in interlayer sliding, formation of stratified tectonic coal, and high degree of coal metamorphism and high gas content, which represent the fundamental reasons why 84.3% of outburst mines in Sichuan Province are located in these two regions. According to the tectonic control law and characteristics of coal seam gas occurrence in Sichuan Province, the gas occurrence zones of coal seam in Sichuan Province were divided into three high gas and outburst zones, three high gas zones and one low gas zone; in addition, their tectonic control characteristics and gas occurrence characteristics were analysed.