Study On The Gas Geology Characteristics Of Dacao Coal Seam At Qingshan Coal Mine In Pingxiang Mining Area

Qingshan Coal Mine is a important producer of anthracite in Jiangxi province and the main coal seam is Dacao coal seam, with complicated geological structure, which is a steep seam mining and the high gas outburst mine. With the development of mining depth on coal seam, the mine gas prevention and control work is becoming even more serious.Through the collection of geology and gas geological data and the field research, Dacao coal seam is divided into two geologic units from the geologic aspect in this article, namely, the eastern and the western gas geological unit according to the Jianshanchong reverse fault and Dishuiyan reverse fault. This paper analyzes the gas content and gas composition, and estimates the lower limit of gas weathered zone, which is 98.43m. It is established that the mathematical relationship between the gas pressure and the elevation, the gas content and the depth of burial, and the gas content and the volatile matter of coal from the information of Qingshan coal mine. The influence on the distribution of the degree of coal metamorphism for the gas content at Dacao coal seam is duscussed. Gas content of the Dacao coal seam can be divided into three areas based on the metamorphic volatile. The control function of geological structure on the gas occurrence in coal seam is evaluated. The paper has the statisticses of the rock of roof and floor and combination characteristic, draws the roof lithofacies zoning map, and calculates the ratio of sand and mud of roof and floor, the roof rock characteristics influence on the gas content through the core recovery. The article also uses the exploration drilling well logging curves to identify the development of tectonic coal, at the first time in Dacao coal seam, provides the basis for the prediction of gas outburst at new area.This paper shows that:geological structure is the dominant factor in the uneven distribution of coal bed methane. The gas pressure and the gas content were significant positive correlation with elevation, but the variation characteristics on the change of the gas content gradient in the depth is different. There are anthracite and high metamorphic bituminous coal in Dacao coal seam. The degree of coal metamorphism of Dacao coal bed is different in horizontal and vertical, influencing on the distribution of gas content. The higher grade of coal metamorphism, the greater of the gas content. The roof and floor of Dacao coal-bed are mudstone, shale, carbonaceous shale or siltstone. The ratio of sand and mud is relatively small. With the roof and floor of complete compaction, which has little effect on the gas occurrence. The development of tectonic coal is very well in Dacao coal bed, and the shallow of tectonic coal in Dacao coal seam had happened gas outburst. Therefore, the new places of the tectonic coal development has the danger of outburst.This research will provide basic conditions for the production, the disaster prevention of gas and the development of gas resources.