煤层中双重孔隙介质渗流理论的应用

 考虑煤层气稳定解吸和不稳定解吸特征,提出了两类窜流方式不同的双重孔隙介质煤层不定常渗流模型——双重孔隙介质煤层拟稳态和不稳态窜流不定常渗流模型.用有限体积法对其求解,并分析了两类模型在不同地质参数情况下的特征曲线.结果表明,稳定解吸和不稳定解吸现象的存在都延缓了煤层中压力波的传播;解吸系数的增大使煤层压降变缓,且在压力和压力导数曲线上表现为边界距离的增大.对于不同的煤层,当窜流系数过大或过小,或煤层储能系数过大时,计算得到的理论曲线不能表现出双重孔隙介质特征.这与现场测试资料曲线较难出现双重孔隙介质特征一致,从而找到了现场煤层测试难以出现双重介质特征问题的根源.

Theory of Dual-porosity Media in Coal Bed Methane and Its Application

Considering the effects of both steady and unsteady desorption of Coal Bed Methane(CBM), two kinds of dual-porosity unsteady seepage models are developed, including pseudo-steady cross-flow model and dual-porosity unsteady cross-flow model. The two models are solved by finite volume method and their characteristic curves are analyzed by considering different geological parameters. The calculation results show that both steady desorption and unsteady desorption of CBM delay the propagation of pressure wave; the increase of CBM desorption coefficients makes the pressure draw down slowly in the coalbed, it manifests the increase of boundary distance in pressure and pressure derivative curve. For different coalbeds, when either the cross-flow flow coefficient or the fracture storage coefficient is oversize, the dual-porosity media characters in theoretical curves will be covered up. The fact is consistent with the field test data which are difficult to appear the dual-porosity media characters. Therefore the root of the problem is discovered based on the research, while the field test data is hard to show the dual-porosity media characters.