Research on gas occurrence regularity in Fengcheng Mining Area of Jiangxi Province

摘要

The hazard of coal and gas outburst and the utilization of coalbed methane, continuously promotes research on the characteristics of methane distribution. As an important coal production base in China, Fengcheng Mining Area not only is serious in coal and gas outburst but also is one of the most promising coalbed methane development zones, so it is of significance to research on gas occurrence regularity. Based on the analysis of gas data collected from geological exploration and coal mining, the research reveals that: the gas occurrence regularity vary significantly between north limb and south limb of Fengcheng syncline. In north limb, with the increase of the depth of coal seam, gas content of coal seam tend to increase, the relative gas emission rate and the absolute gas emission rate tend to increase, the intensity of coal and gas outbursts tend to increase. But in south limb, the gas contents of coal seam are very low, far below the gas contents in north limb under the same depth. The controlling factors to gas occurrence regularity are discussed in this paper. The features of coal quality, the overlying lithology of coal seam and coal body structure in Fengcheng Mining Area are all favorable to gas generation and gas preservation. Under these conditions, in north limb, with the increase of coal seam's depth and overlying pressure of coal seam, the risk of gas hazard increase, which cause the gas occurrence regularity in north limb of Fengcheng syncline. But in south limb, the Eocene strata of Paleocene is directly overlying above Longtan coal-bearing strata of the Permian, which means that the coal seams of south limb have ever been strongly uplifted and exposed to ground so as to be weathered and eroded for a long time, and a large amount of gas is released, thus the gas contents of B4 coal seam in south limb are very low.