A gas outburst prevention and control strategy for single thick coal seams with high outburst risk: A case study of Hudi Coal Mine in Qinshui Basin

Coal and gas outburst is one of the most harmful natural disaster in coal mine production. The frequency and scope of outburst are closely related to the metamorphic degree of coal seam, the depth of coal seam, and the complexity of geological structure. In general, the use of traditional along-seam borehole or cross-seam borehole can meet the needs of gas control. However, for the coal seams with high outburst risk, these methods fail to meet the demands of high-yield and high-efficiency coal recovery as well as safe, green, and economical coal mining. Although pressure-relief gas extraction in the protective seam and coalbed methane (CBM) pre-extraction can eliminate outburst risk in coal seams, these methods can hardly help realize the green development trend of coal and CBM co-extraction because they cannot guarantee the current situation of highly mechanized mining. In this study, a three-dimensional coal and CBM co-extraction strategy was proposed. The strategy includes three levels of three-dimensional gas prevention and control methods. The first level is the combination of ground and underground gas extraction methods, to achieve joint extraction of ground and underground gas. The second level is the full-coverage extraction of the coal resources to be mined, to achieve joint extraction through upper and lower cross-seam borehole and along-seam borehole. The third level is the optimization of ground and underground extraction and utilization systems, to realize the full utilization of CBM and to achieve the goal of coal and CBM co-extraction. The three-dimensional gas prevention and control method constructs a new gas control model for single thick coal seams with high gas outburst risk and realizes the all-round coordination and unity of different gas control methods spatially and temporally. The gas control strategy completely eliminates the high gas outburst risk of a single thick coal seam and has been successfully applied in Hudi Coal Mine. The application results verify that the method can effectively guarantee the operation safety during highly mechanized mining, realize extraction and full utilization of separate-source gas, and provide guidance and direction for coal and CBM co-extraction with similar extraction conditions.