Geological control factors and characteristics of gas occurrence in Chongqing coal mining area

In this study, the control factors and distribution characteristics of coal seam gas occurrence are emphasized in large regional tectonic background. Due to the inheritability between ancient and modern tectonic stress fields in Chongqing coal mining area, the coal-bearing formation bears long term effect of stress concentration and cannot be relaxed. Therefore, this makes the coal and gas outburst occur primarily in the stress concentration area of more intense tectonic movements. The tectonic stress field and the sedimentary environment of coal-bearing formations are two major geological factors in controlling gas occurrence. Longtan Formation is mainly of bay-tidal-peat swamp facies, which indicates that it has great sealing ability to reserve gas, and the gas content is generally high. However, the coal seam gas content of Xujiahe Formation is generally low, because in Xujiahe Formation the ability of reserving gas is poor, sedimentary systems of river alluvial plain and lakeshore-delta had been developed. Finally, six regional gas geological zones are defined, including Nantong high outburst gas zone, Huayingshan high outburst gas zone, Yongrong high gas zone, southeast Chongqing gas zone, east Chongqing gas zone, and Dabashan high gas zone.