Application of pneumatic directional drilling technology for soft-fragmentized coal seam in Qinglong Coal Mine

In view of problems of rotary drilling technology for soft-fragmentized coal seam, such as shallow borehole completed depth, uncontrollable borehole trajectory, low drilling efficiency and poor gas drainage effect, pneumatic directional drilling technology was put forward to carry out gas drainage borehole construction in soft-fragmentized coal seam. Compressed air output by underground explosion-proof air compressor is used as drilling power and slag discharge medium. Wired measurement while drilling device is used to obtain borehole trajectory parameters. Compressed air monitoring device is applied to monitor parameters such as air supply pressure, temperature and flow rate in real time, which provide basis for judgment of working condition in borehole. In order to realize efficient coal dust treatment, compressed air dust removal device is used to purify coal dust in orifice. The field test was carried out in drilling field of southern region of 21608 roadway in Qinglong Coal Mine of Yankuang Guizhou Nenghua Co., Ltd. The pneumatic directional drilling technology was adopted to construct directional boreholes in soft-fragmentized coal seam with firmness coefficient of 0.37. The maximum borehole depth is 345 m, and the average effective footage of single shift is more than 30% higher than that of ordinary rotary borehole.The average gas drainage volume fraction of single borehole remains at about 70%, which is about 60% higher than that of ordinary rotary borehole. The average gas drainage volume fraction of main pipeline in drilling field is 71.2%, the average gas drainage purity is up to 4.0 m3/min, and accumulated gas drainage volume reaches 115 000 m3, which effectively covers gas drainage area of 300 m roadway to be excavated. The pneumatic directional drilling technology has advantages of controllable borehole trajectory, long borehole completed depth, high drilling efficiency and good gas drainage effect. It can be applied to gas regional drainage and pre-drainage in soft-fragmentized coal seam, which provides a new technical approach for gas control in soft-fragmentized coal seam.