Research on efficient drilling technology in hard-soft compositecoal in Changping Mine

In order to solve the problem of shallow drilling hole in Changping coal seam, the research on efficient drilling technology in hard-soft composite coal was carried out. According to the characteristics of hard-soft composite coal seam, the drilling technology which uses medium to high speed, wide blade and high helix compound drilling method is put forward. Based on the mechanism of slag discharge of helix drill, two different drilling tools that were ø110/63.5 mm spiral drill pipe +ø120 mm three-wing alloy drill bit and ø95/60.3 mm spiral drill pipe +ø110 mm three-wing scraper PDC drill bit, are designed and manufactured, and the high speed unit head of ZDY6000LR drilling rig is improved. Using ZDY3000LG, ZDY6000LR drilling rigs combined with the manufactured drilling tools, a three-stage industrial test was carried out. Accordingly, a helix compound drilling technique which mainly includes the mechanical discharge by means of medium to high speed helix supplemented with fly-ash discharge by using wind power is formed. The rate of resultant boreholes in Changping Coal Mine with depth greater than 150 m is up to 52% and thus the drilling efficiency in the borehole along the hard-soft composite coal seam has been further improved.