有效应力对煤样变形和渗透性的影响研究

Effects of the effective stress on deformation and permeability of coal

为了研究渗透率随有效应力的变化特征,利用含瓦斯煤热–流–固耦合三轴伺服渗流装置,在外部应力不变、降低进口气体压力,外部应力、进气口压力同步降低2种实验条件下,观测了赵各庄煤矿9号煤层样品的应变和气相(氦气)渗透率,研究有效应力对煤样变形和渗透性的影响。实验结果显示,随着有效应力升高,煤样的收缩应变加剧,有效应力为5.2~6.5 MPa,收缩体积应变与有效应力之间符合线性关系,有效应力大于6.5 MPa或小于5.2 MPa,应力–应变曲线发生偏折,部分煤样出现扩容现象;气体渗流速度随进口气体压力的降低而降低;升高或降低有效应力,煤样渗透率均随着进口气体压力的降低而增大。由此可见研究有效应力变化条件下的渗透率变化特征,应适当考虑气体滑脱效应的影响。

In order to investigate the effect of the effective stress on deformation and permeability of coal,the strain and permeability of coal cores from No. 9 coal seam of Zhaogezhuang Coal Mine in Kailuan Mine area were measured with the triaxial servo-controlled seepage device. The experiments were carried out under two types of conditions. One type of condition was to reduce the inlet gas pressure while the confining stress was kept constant. Another type of condition was to reduce the gas pressure and confining stress synchronously. The coal shrinkage was found to increase with the effective stress. There was a linear correlation between the volumetric strain of coal and the effective stress within the range of 5.2 MPa and 6.5 MPa. When the effective stresses were outside the range,the stress-strain lines were not straight anymore,and coal dilatation was observed from some samples. The gas flow velocity decreased with the decreasing of gas pressure of inlet port. However the coal permeability increased regardless the decreasing or increasing of effective pressure. Therefore the effect of gas slippage should be considered when the coal permeability change with effective stress is investigated.