煤层注水驱替瓦斯前缘的渗流规律研究

Study on Seepage Law for the Front of Gas Displacement by Coal Seam Water Injection

煤层注水驱替瓦斯前缘在数学上是一个气水交接的间断界面,渗流过程比较复杂。为了研究间断界面上水驱气前缘水相饱和度的变化规律,采用Comsol Multiphysics有限元多物理场耦合模拟软件对煤层注水驱替瓦斯渗流过程进行了数值模拟。根据模拟得出的气水两相相对渗透率的变化情况,引入一维块网格系统的三阶TVD格式和四阶TVD格式进行驱替前缘的计算。从而得出注水前沿的水相饱和度分布规律：两相驱替前缘水相饱和度在0.2-0.7之间下降很快,呈先下降,后保持平稳值的趋势。该方法具有很好的间断捕捉能力,对于间断的可压缩流体运动有较高的分辨率又不产生虚假数值震荡,为进一步研究分析注水提高煤层瓦斯运移的机理提供基础。

The forefront of coal seam water injection gas displacement in mathematics is a transition discontinuous interface of gas and water,the seepage process is relatively complex.In order to study the change law of the water saturation on the discontinuous interface,the seepage process of gas displacement by coal seam water injection is simulated with Comsol Multiphysics finite element simulation software.According to the changes of the relative permeability of gas phase and water phase by simulation,the third order TVD format and fourth order TVD format of one dimensional black grid system has been used to calculate the front of gas displacement.The water saturation distribution law of water injection front is obtained that the water saturation decreases rapidly at 0.2 to 0.7,which decreases at first and then maintains a steady trend.This method has a good intermittent capture ability,which has higher resolution for the compressible fluid motion and does not produce false numerical oscillation.The results provide the basis for further study on mechanism of the coal seam water injection to improve gas migration.