Numerical simulation of gas drainage from goaf via high-level borehole in gently inclined seams

Gas disasters pose a significant constraint on the safe development of coal mines. Focusing on the problem of gas over-limits in the upper corner of a hard roof, this study takes the I010206 working face of Kuangou Coal Mine as a case study and proposes a high-level borehole gas extraction method. Initially, FLAC3D was employed to analyze the development pattern of the “three zones” in the overlying strata of the working face. The results revealed that the height of the fractured zone in the I010206 working face is approximately in the range of 30–90 m. Subsequently, COMSOL was utilized to elaborate on the effective extraction radius of boreholes. The influence laws of factors such as extraction time and borehole arrangement on the extraction effect were analyzed, and an optimized borehole-layout plan for high-level borehole gas extraction was put forward. Furthermore, based on the above-mentioned analysis, FLUENT was used to establish a borehole gas extraction model to study the gas extraction effect of high-position boreholes arranged in the fractured zone. The research demonstrated that the triangular-pyramid-type borehole layout is reasonable and effective. In addition, the optimal vertical height for high-level drilling was found to be 28–32 m from the roof, and the optimal horizontal distance is 10–15 m from the model boundary. These findings are expected to offer technical references and guidance for gas control in the upper corners of hard roofs.