蠕变-渗流耦合作用下水力冲孔周围煤体渗透率时空演化规律

Reseach on coal permeability spatio-temporal evolution around hydraulic flushing based on creep-seepage coupling

为了研究水力冲孔周围煤体瓦斯运移规律,研究了水力冲孔周围煤体的应力、体积应变和孔径变化规律,建立了蠕变-渗流耦合作用下的水力冲孔周围煤体渗透率动态演化模型,揭示了水力冲孔周围煤体渗透率的时空演化规律,阐明了蠕变变形和基质收缩对渗透率的控制作用机理。研究结果表明:水力冲孔措施可以大幅度提高钻孔周围煤体的渗透率,在空间上煤体渗透率随距离呈负幂函数关系迅速降低(K=2×10^(-16) r^(-2.4));在时间上煤体渗透率随抽采时间的延长而逐渐增大,但是增加梯度会逐渐降低;水力冲孔周围煤体渗透率的增加主要受到煤的蠕变变形控制,基质收缩效应虽然有利于渗透率的增加,但对渗透率的贡献远小于煤体的蠕变变形;钻孔由于蠕变变形会产生缩孔现象,很容易堵塞抽采通道,此时即使渗透率大幅度的提高,也很难保证抽采效果,因此迫切需要制定相应的防堵孔措施。

In order to study gas migration rule around hydraulic flushing,the stress,volumetric strain and borehole aperture variation were analyzed,the dynamic evolution model of coal around hydraulic flushing based on creep-seepage coupling,the coal permeability spatio-temporal evolution around hydraulic flushing was revealed,and the control mechanism of creep deformation and matrix shrinkage on permeability was illuminated. The results show that： hydraulic punching measures can greatly improve the coal permeability around boreholes,the coal permeability decreases quickly in negative power function with increasing of hole wall distance（K=2×10^（-16）r^（-2.4））,and the coal permeability increases gradually with increasing of extraction time,but the increase gradient will reduce gradually; The increase of coal permeability around hydraulic flushing is mainly affected by creep deformation,and the matrix shrinkage effect is conducive to the increase of permeability,but it is much smaller than the contribution of creep deformation; shrinkage phenomenon of borehole occurs over time because of creep deformation,which is easy to block gas drainage channel,In this case,even if permeability is greatly improved,it is difficult to improve drainage effect,so there is an urgent need to develop anti blinding measures.