Key technology of pressure-relief gas extraction in low dynamic fracture zone of mining overburden in single ultra-thick coal seam

SHU Longyong; ZHANG Yuanlong; SONG Xin; FAN Yongpeng; LI Yang

doi:10.12438/cst.2024-1945

Abstract：Different from the high gas and prominent mining areas in the middle east of China,the mining face of single thick and extra thick coal seam in the western mining area has a large amount of unloading gas and mainly originates from this coal seam,if the mining overburden unloading gas extraction drill holes are arranged in the fissure zone according to the traditional viewpoint,it is difficult to ef-fectively control the gas in the upper corner of the mine,although the concentration of the extracted gas is large.In order to study the op-timal arrangement area of long directional drilling holes in the roof slab of a single comprehensive mining face of extra-thick coal seam in western mining area,based on the comprehensive mining face of extra-thick coal seam in a mine in Yonglong Mining Area,the combina-tion of theoretical analysis,numerical simulation and on-site engineering practice has been used to study the structure of the roof slab of the comprehensive mining face of extra-thick coal seam,and the characteristics of the dynamic development of the collapsed fissures exis-ted in the roof slab of the roof slab at the back of the face,so that it is proposed that there is a low level of pressure relief gas extraction be-fore stabilization of the mining overburden of extra-thick coal seam.It is proposed that there are low dynamic collapse zone and low dy-namic fissure zone before stabilization of mining overburden,and through the combination of theoretical analysis and numerical simula-tion,it is determined that low dynamic fissure zone is the optimal arrangement area of long directional drilling holes in the roof direction of a single extra-thick coal seam,and the rationality of the arrangement is verified through the engineering practice,and it is explored that the scope of low dynamic fissure zone is related to the thickness of the coal seam mined,the rock properties of the overburden,the key layer of the direct top,the inclination angle of the coal seam,and the mining speed of the working face back to the mine.The relationship between the scope of low-level dynamic fissure zone and the influencing factors such as mining thickness,overburden lithology,direct roof key lay-er position,coal bed inclination angle and working face mining speed is discussed.Field engineering practice shows that,after optimizing and adjusting the directional long drilling arrangement parameters based on the scope of the low dynamic fissure zone,the average propor-tion of air-drained gas decreased by 4.4％,the average single-hole unloading gas extraction efficiency increased by 75.7％,and the gas con-centration in the upper corner of the corner was 0.48％at the most,while the number of holes was reduced by 3,and the overall amount of drilling work was decreased by 28.7％.Under the conditions of integrated mining of a single extra-thick coal seam,arranging long direc-tional drilling holes for the roof plate in the low dynamic fissure area can ensure sufficient effective extraction length,and at the same time accurately and efficiently extract the dynamic unpressurized gas and reduce the risk of gas exceeding the limit in the working face.The re-search result enriches the theory and technology system of mining overburden pressure relief gas extraction,and can provide certain theor-etical and technical support for solving the problem of gas overlimit in the upper corner of the working face of single extra-thick coal seam comprehensive mining in the western mining area.