煤基质变形影响下含瓦斯煤渗透率动态变化规律

Dynamic change laws of the permeability of coal containing gas under the effect of coal matrix deformation

煤层渗透率不仅直接影响着煤层气(俗称瓦斯)抽采的效果,而且还是计算瓦斯涌出量的关键参数。为了明确不同压力条件下含瓦斯煤渗透率的变化规律,通过考虑有效应力和甲烷吸附/解吸对煤渗透率的综合影响,建立不同压力下含瓦斯煤渗透率动态演化模型;进而以山西晋煤集团岳城矿钻取的煤样为样品,开展了三轴应力状态下的渗透率测试实验,并将实验测试结果和模型计算结果进行对比,进而探讨不同压力下含瓦斯煤渗透率的动态变化规律。研究结果表明:①渗透率与压力的关系曲线呈不规则的“U”形,在相对低压阶段,随着压力增加,煤基质表面的甲烷吸附量增加,煤岩膨胀变形对渗透率的影响占主导地位,渗透率迅速减低,随着压力逐渐增加,甲烷吸附量达到饱和,有效应力对渗透率的影响占主导地位,渗透率小幅度回升;②实验结果和模型计算结果基本吻合,并且变化趋势也一致。结论认为,所建立的含瓦斯煤渗透率动态演化模型可靠,可以为煤与瓦斯突出防治及煤层气有效开采提供技术支撑。

Coal permeability not only has a direct effect on the exploitation effect of coalbed methane(commonly called gas),but also is the key parameter in the calculation of gas emission.In order to investigate the variation laws of the permeability of coal-containing gas under different pressures,it is necessary to establish a dynamic evolution model of the permeability of coal-containing gas under different pressures by considering the comprehensive effects of effective stress and gas adsorption/desorption on coal permeability.Then,a permeability measurement experiment under triaxial stress state was carried out on the coal samples taken from Yuecheng Mine Field of Shanxi Jinmei Group.Moreover,the experimental results and model calculation results were compared.Finally,the dynamic variation laws of the permeability of coal-containing gas under different pressures were discussed.And the following research results were obtained.First,the permeability–pressure relationship curve is in an irregular"U"shape.In the phase of lower pressure,as the pressure increases,the amount of the gas adsorbed by the surface of coal matrix increases,the influence of coal rock expansion deformation on the permeability is dominant and the permeability decreases rapidly.As the pressure gradually increases,the gas adsorption capacity gets saturated,the effect of effective stress on permeability gradually dominates and the permeability increases slightly.Second,the experimental results and the model calculation results are basically accordant and their variation trends are also consistent.It is concluded that the proposed dynamic evolution model for the permeability of coal-containing gas is reliable and can provide technical support for the prevention of coal and gas outburst and the effective exploitation of coalbed methane.