考虑煤体蠕变的瓦斯渗流规律及抽采钻孔布置

Gas seepage law and drainage borehole layout considering coal body creep

为了研究深部煤体蠕变对瓦斯渗流的影响,建立了考虑蠕变作用下煤体变形场、瓦斯扩散场及瓦斯渗流场多场耦合的数学模型,以陕西彬长胡家河矿业有限公司煤层瓦斯赋存及地质条件为依据,模拟分析了煤层瓦斯抽采动态变化规律,通过现场监测验证了数学模型的正确性、合理性、可靠性及工程适用性。研究结果表明:①煤层瓦斯压力随距抽采钻孔距离的增加而增大,距钻孔越近,瓦斯压力梯度越大,煤体渗透率比值越大,在远离钻孔处瓦斯压力和渗透率比值均逐渐趋于稳定。②在瓦斯抽采初期,距钻孔越近煤体的瓦斯压力降低幅度越大,随着抽采时间延长,瓦斯压力降低的幅度逐渐变缓;在瓦斯抽采初期,距钻孔较近煤体的渗透率比值增加幅度较大,随着抽采时间的延长,在应力和瓦斯压力共同作用下,煤体的蠕变变形导致渗透率比值增加的趋势趋于平缓。③与单孔瓦斯抽采相比,双孔抽采可显著降低煤层瓦斯压力;钻孔间距越小,不同抽采时间内两钻孔间的瓦斯压力梯度越小,但随着抽采时间延长,瓦斯抽采效率越低;结合陕西彬长胡家河矿业有限公司瓦斯赋存条件,确定其瓦斯抽采钻孔最合理间距为2m。

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:①The 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.②During 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.③Compared 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.