Slag discharge characteristics and engineering application of prismatic grooved drill pipe in borehole collapse

Gas drainage through underground boreholes is the main method for gas control and utilization in soft high gassy seam. However, this method has technical problems including shallow drilling depth, low drilling efficiency, and frequent engineering accidents. This paper proposes a prismatic grooved drill pipe. To verify its slag discharge effect, a numerical model of the slag discharge of the borehole collapse area was established. Furthermore, the running time, velocity, and static pressure of the drill cuttings in the borehole were tracked and analyzed. The research results show that the prismatic grooved drill pipe forms three slag discharge channels in the collapse area. This improves the slag discharge efficiency and reduces the probability of clogging in the collapse area. These, in turn, can effectively overcome the influence of the collapsed hole on the drilling. The prismatic grooved drill pipe was used in the Xinyuan Coal Mine. The field test results show that (1) the slag discharge effect was good, (2) the drill pipe did not get stuck or broken during drilling, (3) the average borehole depth attained a design depth of 130 m, and (4) the deepest borehole was 200 m.