Practice and effect analysis of ultra-long directional borehole gas extraction in coal seam

Based on the requirements for improving the production capacity of the mine and mining in the deep area of Baode Coal Mine, a gas advanced treatment mode with the panel as the unit has been put forward. That is to say, the panel is covered at one time by using a group of ultra-long directional boreholes. Through long-term, stable and efficient gas drainage, comprehensive advanced treatment of gas in the panel before mining can be achieved. This paper introduces the borehole completion technology and complete set of drilling equipment for ultra-long directional boreholes for gas drainage along the coal seam. Through engineering practice, technical breakthroughs in the depths of ultra-long directional boreholes along the coal seam of 2 311 m, 2 570 m and 3 353 m have been completed successively. On this basis, the statistics of gas drainage data from ultra-long directional boreholes along the coal seam for more than five years have been carried out. The cumulative pure gas drainage amounts of the three boreholes have exceeded 8.43 million cubic meters, 7.54 million cubic meters and 12.81 million cubic meters respectively. The gas drainage amounts in the past three years have been analyzed, and the variation trends of the gas drainage amounts and drainage concentrations of ultra-long directional boreholes along the coal seam with the drainage time have been revealed. Through budgetary estimates, the drainage radii of the three boreholes have reached 153 m, 123 m and 160 m respectively. Practice shows that the gas drainage amount of ultra-long directional boreholes along the coal seam decays slightly over time and has the conditions for long-term and stable drainage, which can realize the advanced treatment of gas in large areas of large modern high-gas coal mines.