Key technology and practice of directional drilling for gas drainage in all the mining time and space in underground coal mine

To meet the urgent need for efficient gas control in high gas,and coal and gas outburst mines and realize a comprehensive and accurate gas drainage,the modes of gas drainage in the broader stope area of medium hard coal seam,the region of broken soft coal seam and the mining area for borehole instead of roadway are proposed. Taking advantage of accurate and controllable directional borehole trajectory and long distance extension along the target stratum,the gas drainage for medium hard coal seam,broken soft coal seam and roof stratum in a large region of underground coal mines can be accurately covered. The whole period of pre mining,production process and mined gas can be continuously extracted,so as to realize the gas drainage in different formations and mining times,and complete extraction to the greatest extent. The requirements and gas treatment for gas control under the different geological conditions of coal seam and mining stages are comprehensively expounded,the technical difficulties of directional drilling in medium hard coal seams,broken soft coal seams and complex roof strata are systematically analyzed. On this basis,the directional drilling technology for super long borehole in the medium hard coal seam,the pneumatic directional drilling technology in the broken soft coal seam,and the large diameter directional drilling technology in the complex roof strata are developed,and the applicable conditions and main characteristics of each key technology are analyzed. The industrial test and demonstration application are carried out in typical underground coal mining area in China. The engineering practice shows that the maximum directional borehole depth in a medium hard coal seam is 3 353 m,which realizes the gas drainage and control in a broader stope area of the mine. The borehole forming rate in a broken soft coal seam with a directional borehole depth of more than 300 m reaches 76%,which realizes the accurate extraction of coal roadway strip and advanced area of coal face. The depth of directional borehole in a complex roof strata generally reaches more than 500 m,and the diameter of one time reaming can reach 200 mm,which promotes the technological development of boreholes instead of roadways for gas drainage. The research can provide technical equipment support for the realization of the goal of “zero overrun” of mine gas and “zero outburst” of coal seam.