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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.

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Coal and gas outburst accidents occur most frequently during coal uncovering operation, and uncovering-induced outburst accidents have caused great economic losses and casualties. In order to quickly and safely uncover the outburst coal seam at the air intake shaft in panel 2, Zhaozhuang Coal Mine has come up with the technology of multibranch radial borehole hydraulic fracturing (MRBHF) coal uncovering technology in the surface coalbed methane (CBM) well. By conducting fracturing of constructed radial boreholes in the CBM well, the technology increases fractures, enhancing coal permeability and raising gas drainage volume in the uncovering area. It brings the following three major benefits: (1) uncovering coal efficiently, rapidly, and safely; (2) greatly reducing engineering quantity, coal uncovering period, and construction cost, i.e., significantly improving the economic benefits; and (3) efficiently reusing the CBM well. Compared with conventional uncovering measures, the proposed technology shortens the uncovering period by 118 d, enhances the coal seam permeability by 3.55 times, raises the gas drainage rate by 22%, increases the gas drainage volume by 1.93 times, and reduces the engineering volume of drilling by 12,000 m. The safe, rapid, economical, and applicable technology provides scientific guidance and reference for domestic and foreign shaft coal uncovering engineering and possesses important economic and social values and application prospect for safe and efficient production of coal mines.

Pore difference characteristics and adsorption/desorption experiments of primary coal with different degrees were explored to study the characteristics of pore structure and gas desorption. The results show that the pore volume increases with the increase in the degree of metamorphism. In primary coal with different degrees of metamorphism, the distribution of micropores, small pores, and medium‐sized pores (by volume) is WY < PM < CY. The distribution of large pore volume and visible pore volume was WY > PM > CY. According to the pore volume distribution law of different metamorphic primary coals, the average pore diameters of WY, PM, and CY were 68.40, 45.60, and 30.50 nm, respectively. The porosity and specific surface area of primary coal with different degrees of metamorphism show a distribution pattern such that WY > PM > CY. For large pore and visible pore, the pore volumes of WY, PM, and CY coal were 0.0785, 0.0587, and 0.0300 mL/g, respectively, and the proportions were 81.86%, 74.49%, and 55.25%, respectively. The porosity of WY, PM, and CY were 11.57%, 9.03%, and 6.57%, respectively, and the specific surface areas were 6.917, 5.826, and 5.611 cm3/g. According to the desorption characteristics of coal bodies with different metamorphic degrees at different time nodes found that the gas desorption at different time nodes shows similar changes under the same adsorption equilibrium pressure. The higher the degree of coal metamorphism, the greater the amount of gas desorption, and the faster the desorption amplitude. The desorption intensity of WY coal is significantly higher than that of PM and CY coal with the increase of desorption time which also verifies the measurement results of pore structure and adsorption constant.