Abstract
Outburst coal seam and high gas coal seam and using borehole to extract coal seam gas are the main measures to prevent coal and gas outburst, reduce gas emission and reduce air flow gas overrun in working face. Increasing borehole diameter and improving coal seam permeability are one of the common methods to improve the effect of this measure. In this paper, the drilling and expanding integrated bit is developed and designed to improve the construction efficiency. Firstly, the mechanical analysis of high-pressure water jet combined with coal breaking of drilling teeth is carried out to provide the basis for the optimization of drilling and expanding integrated bit. The optimization principles of bit and nozzle are put forward respectively. The bit material is optimized. The hardness is increased by 20 ~ 40 times by using diamond composite chip (PDC) bit. Through numerical simulation analysis, it is determined that when the nozzle l/d value is 2, the jet development can maintain good stability. The nozzle is arranged with 2 ~ 3 nozzles in radial direction and 1 ~ 2 nozzles in axial direction, and the best contraction angle is 13 ° ~ 15 °. The field test shows that the average equivalent diameter of coal 6 after reaming is 720mm, which is 9.6 times that before reaming, and the effect of reaming and pressure relief is remarkable.
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