Improvement of drilling quality using precision directional drilling technology

The problem of boreholes deflection in coal mines is common, especially in soft and hard composite coal seams. As a result, the distribution of boreholes is uneven and forms a blank zone in the drainage area, which fails to achieve the regional pre-draining, causing gas explosion or coal and gas outburst accidents. Aiming at the above problems, this paper developed the technology of anti-inclination for drilling based on the causes of borehole deflection in detail. The anti-inclination advice integrates straight keeping, slag removal and smooth back drilling with reasonable technical parameters. Full hole drilling was adopted to realize straight drilling. Three spiral grooving, vertical grooving and three-edge short-circuit were adopted for collaborative slag removal. Three alloy pieces were welded at the rear end of anti-inclination device to act as reverse drill bit, realizing smooth drilling withdrawal. For sticking problems, we improved the anti-inclination device. Three 20 mm millimeters wide vertical grooves were milled in each 120° direction around the device. After using the improved anti-inclination device, the average deviation of dip and azimuth was only 4.8 and 4.5 degrees, respectively, which were reduced by 51 and 44%. The borehole offset was reduced from 9.9 m to 2.9 m, a decrease of 71%, which improved the gas drainage effect and ensured the safe production of the mine.