Gas seepage law and drainage borehole layout considering coal body creep

In order to research influence of deep coal body creep on gas seepage, mathematical models of multi-field coupling including coal body deformation field, gas diffusion field and gas seepage field were established considering creep action. Based on gas storage and geological conditions of Shaanxi Binchang Hujiahe Mining Co., Ltd., dynamic variation laws of gas drainage from coal seam were analyzed by numerically simulation. The validity, rationality, reliability and project usability of the mathematical models were verified by field test. The research results show that: ① The gas pressure in coal seam increases with distance increase from drainage borehole. The closer to the borehole, the larger the gas pressure gradient is and the greater the coal body permeability ratio is. The gas pressure and permeability ratio are gradually stable at the place away from the borehole. ② During the initial stage of gas drainage, gas pressure near the borehole decreases greatly. With the extension of drainage time, gas pressure reduction becomes slower gradually. During the initial stage of gas drainage, permeability ratio of coal body near the borehole increases greatly. With the extension of drainage time, coal body creep deformation causes permeability ratio to increase slowly under combination effects of stress and gas pressure. ③ Compared with single-borehole gas drainage, double-borehole gas drainage can significantly reduce gas pressure in coal seam. The smaller the boreholes spacing is, the smaller the gas pressure gradient between two boreholes is at different drainage time, but lower the drainage efficiency is with the extension of drainage time. According to gas storage conditions of Shaanxi Binchang Hujiahe Mining Co., Ltd., the optimal boreholes spacing of gas drainage is 2 m.