Movement Law of Methane Drained by Large-Diameter Borehole Drilling Machine in the Goaf

Abstract

To study the movement law of methane in the goaf drained by a large-diameter borehole drilling machine under “U”-shaped ventilation, a simulation on a coal mine was conducted on Fluent to find the optimal spacing between large-diameter boreholes and the most appropriate distance between the borehole and the upper corner. The variation of borehole drilling and the methane concentration in the upper corner were obtained through a field test. Results show that the method of drilling large-diameter boreholes greatly reduces the methane concentration in the goaf and the upper corner, with the optimal borehole spacing being 30 m and the most appropriate distance between the borehole and the upper corner being 15 m. When the large-diameter borehole is drilled 25 m deep down into the goaf, it penetrates into the stress impact area, and the methane concentration increases rapidly, with the maximum being 3.7%. When the borehole is drilled 35 m down into the goaf, the methane concentration slightly decreases as a result of the drainage superposition effect. The methane concentration in the upper corner increases as the borehole is drilled deeper and is farther away from the upper corner. As a result of the drainage superposition effect, the methane concentration in the upper corner varies from 0.32% to 0.51% in a cyclical way.