Integrated drilling-reaming-discharging technology for pressure relief and permeability enhancement in downward holes of broken soft coal seam

This study addresses the challenges of low coal-breaking efficiency and water accumulation in downward holes within broken soft coal seams. An integrated drilling-reaming-discharging equipment for pressure relief and permeability enhancement was developed, with key operational parameters such as drill rotation speed and propulsion speed being determined. The integrated pressure relief and permeability enhancement technology based on drilling-reaming-discharging was proposed and subsequently applied in Zhongmacun Coal Mine. The field application results demonstrate that the integrated drilling-reaming-discharging technology is unaffected by the submerged environment of downward holes. When the drill rotation speed reaches from 170 r/min to 180 r/min, the resulting centrifugal force controls the opening of the cutting arm, enabling rapid reaming. Positive circulation slag discharge achieves a coal removal rate exceeding 90%, while reverse circulation effectively removes accumulated water from the borehole, thereby ensuring efficient hole construction and unobstructed gas drainage pathways. Following the application of this integrated mechanical cavitation technology, the borehole diameter was enlarged from 120 mm to 600 mm, the effective gas drainage duration was extended from 20 days to 60 days, and within 80 days, the average gas drainage concentration increased from 52.9% to 74.7%, with the average pure gas drainage rate rising from 0.026 m³/min to 0.083 m³/min. These findings indicate that the integrated drilling-reaming-discharging mechanical cavitation technology can effectively address the challenges of pressure relief, permeability enhancement, and slag discharge in downward holes of broken soft and low-permeability coal seams. The research outcomes provide technical support for pressure relief and permeability enhancement in such geological conditions.