探究抽采过程中钻孔瓦斯渗流演化特征对钻孔布置和瓦斯高效抽采具有重要意义.基于双重孔隙介质假设,考虑围岩应力重分布现象对煤层瓦斯渗流特性的影响,建立巷道与钻孔交叉三维结构的煤层瓦斯渗流模型,并对模型进行数值计算,得出煤层中抽采钻孔中瓦斯压力与瓦斯渗流速度的时效特性.结果表明,抽采初期钻孔内外煤层的负压差值比较大,抽采负压为影响瓦斯流动的主要因素.继续抽采孔隙基质发生收缩效应,瓦斯流速幅度△vf逐渐减小并趋于零,并且处于缓慢层流状态.距钻孔不同距离渗透率呈现出较大变化、不稳定性、逐渐减低3种特性,通过判定,3种特性的影响范围为0～1.02 m、1.02～2.75 m,大于2.75 m.
Coupling effect of stress field and seepage field in gas extraction borehole of outburst coal seams
Exploring the evolution characteristics of gas seepage during the extraction process is of great significance for borehole layout and efficient gas extraction.Based on the assumption of dual porous media,and considering the influence of stress redistribution in surrounding rock on the characteristics of coal seam gas seepage,a three-dimensional model of coal seam gas seepage with intersecting roadway and borehole is established,and numerical calculations are carried out on the model to obtain the time-effect characteristics of gas pressure and gas seepage velocity in coal seam's extraction boreholes.The results show that in the early stage of gas extraction,the negative pressure difference between the inner and outer coal seams of the borehole is relatively larger,and the negative pressure of gas extraction is the main factor affecting gas flow.Continuing extraction leads to the shrinkage effect of pore matrix,and the amplitude of gas flow velocity △vf gradually de-creases and approaches zero,and it is in a slow laminar flow state.The permeability shows three characteristics:significant changes,instability,and gradual decrease at different distances from the borehole.The influential ranges of the three charac-teristics are 0～1.02 m,1.02～2.75 m,and greater than 2.75 m.
intersection of roadway and boreholedrilling pressure reliefcoupling calculationgas seepage
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