Development on PDC drill bit used for directional large diameter directional long borehole in borehole instead of roadway

GAO Xiaoliang

doi:10.11799/ce202602029

Abstract：The borehole-instead-of-roadway technology has been gradually promoted and applied in gas extraction from coal mine goafs due to its ability to effectively increase fracture connectivity in the strata,enlarge the gas emission channel area,and thereby improve gas extraction efficiency.Based on the demand for existing large-diameter near-horizontal high-level directional drilling,we employed the helical cutter layout principle to optimize the circumferential arrangement of the blades,enhancing the bit's adaptability to near-horizontal boreholes.The bit profile was optimized to improve steering performance,and the waterway structure was adjusted to ensure effective flushing.Surface additive technology was selectively applied to harden the bit surface.Field trials were conducted with the newly developed bit in high-level"borehole instead of roadway"drilling at a coal mine in Huainan.The results show that when drilling into sandstone and siltstone layers in the coal seam roof,the average service life of two bits reached 1898.5 m.Compared with conventional PDC bits,the new bit shows significant improvements in service life,drilling efficiency,and steering accuracy.During drilling,the bit followed the preset trajectory smoothly,with stable drilling pressure,no whirling,eccentric wear,or cutter breakage.Cuttings were discharged smoothly without pump blockage,and no bit balling or nozzle clogging occurred after tripping out,verifying the rationality of the cutter layout and waterway design.The bit body showed no wear,cracks,or spalling,indicating that the surface additive process is appropriate.The bit meets the requirements for large-diameter directional drilling in"borehole instead of roadway"applications,providing a new solution for the design and manufacture of large-diameter directional bits.