Research on distribution law of dominant gas extraction area of high-level borehole

In order to improve efficiency of gas extraction of high-level boreholes in coal mines, the concept of dominant gas extraction area of high-level boreholes was put forward based on theory of overburden strata mining failure and characteristics of gas migration, that is, the area between caving zone and fracture zone that can guarantee stable and efficient extraction effect.Taking Xiagou Coal Mine as research object, numerical simulation and field verification methods were used to determine dominant gas extraction area of high-level boreholes in ZF302 coal face, and its distribution law was studied. The research results show that the dominant gas extraction area of high-level boreholes in ZF302 coal face is located in the area with vertical height of roof of 33-57 m. In the dominant gas extraction area, the gas extraction volume of single hole shows a trend of first increasing, then becoming stable, and then decreasing. When the height of the final hole is located in the area of 70-57 m, the gas extraction volume of single hole gradually increases from 0.66 m3 /min to 1.48 m3 /min, and then enters the stable area within the height of 57-34 m, and the gas extraction volume of single hole always keeps above 1.0 m3 /min.When the position of the final hole of high-level boreholes is located in the vertical height of 55-65 m, the extraction time of dominant gas extraction area is the longest and the gas extraction quantity of single hole is the highest. After optimization of drilling parameters, the number of boreholes in the drilling field is reduced from 28 to 18, a decrease of 35.71%. The daily extraction volume increases from 26 008.75 m3 to 31 046.4 m3, increasing by 19.37%.