Method and key technologies of underground and surface combined stepwise progressive anti-outburst for deep coal seam groups

Modern high-yield and high-efficiency mines still face the situation of tight replacement among roadway driving, mining and extraction, and put forward higher requirements for the regional scope and advanced time of outburst prevention and control technology. In order to break through the bottlenecks of the existing gas control technology system in the coordinated extraction of near/far coal seam groups and the step-by-step outburst prevention both on the surface and underground, the principle of “spatiotemporal extraction and step-by-step progression” for outburst prevention with the combination of surface and underground operations is systematically expounded. A three-dimensional prevention and control method of “surface advanced pre-extraction for outburst reduction – underground enhanced extraction for outburst elimination – coordinated governance of multiple coal seams” is constructed. By integrating the advantages of spatiotemporal advance of surface wells and the precise control ability of underground operations, a three-level progressive prevention and control system of mine-level regional pre-control, mining area-level coordinated governance and working face-level precise outburst elimination is formed. According to the different characteristics of near and far coal seam groups, the outburst prevention modes of “wide coverage by surface wells and efficient extraction underground” and “enhanced pressure relief underground and multi-source extraction by surface wells” are respectively proposed. By comprehensively using numerical simulation, theoretical analysis and field test methods, a parameter optimization technology for multi-branch horizontal wells with key elements such as the angle between the main well and branch wells and the number of branch wells is systematically constructed. A precise docking technology between surface multi-branch wells and underground directional boreholes is formed by integrating the spatial magnetic field induction model of horizontal well bits and the data of high-precision sensors. The coupling evolution law of the stress field, fracture field and gas seepage field is analyzed, and the distribution characteristics of gas enrichment target areas in deep coal seams are revealed. Combined with the geological conditions and the requirements of the spatiotemporal connection of extraction, the collaborative layout modes of “maximization of a single well area” and “intensive layout in the whole area” for multi-source well groups are proposed. The high-efficiency extraction technology for near coal seam groups is applied in Shaqu No.1 Coal Mine. The total gas production of three multi-branch horizontal wells SQN–0501 after one-year extraction is 7 273 175.4 m³, with an average daily gas production of about 20 000 m³. The key technology of pressure relief extraction for far coal seam groups is applied in Zhuji West Coal Mine. The surface wells have cumulatively extracted 7.283 million m³ of gas from the No.13–1 coal seam, with an extraction rate as high as 81.4%, and the residual gas content is significantly reduced. The effectiveness of this technical system in improving gas extraction efficiency and reducing outburst risks is verified, providing important technical support for the safe mining of deep coal seam groups.