考虑解吸作用的低渗透煤层中双重介质渗流理论研究

根据煤层低渗透和赋存特征,考虑启动压力梯度及解吸的影响,建立了煤层非稳态窜流方式的双重介质渗流模型。利用基于delaunay网格的有限体积法(FVM)对模型进行求解,得到了双重介质低渗透煤层试井理论曲线,并分析了模型在不同地质参数情况下的双对数曲线的特征。结果表明:基质储能系数越大,对生产越有利。只有当压力梯度大于启动压力梯度时,流体才能流动。解吸现象的存在延缓了煤层中压力波的传播,因此煤层气(CBM)开发早期需要缓慢排水,尽可能将压力降落传播到较大范围形成面积降压,有利于提高CBM的最终采收率。

Dual Porosity Modeling with Desorption for Low Permeability Coal Seam

According to the unusual characteristics of low permeability and adsorption of coal seam, the unsteady crossflow of dual porosity model which considers the effects of desorption and starting pressure gradient is established. The model was solved by finite volume method (FVM) on delaunay to gain the type curves, and the characteristics of different parameters were analyzed. The results show: the larger storage coefficient of matrix is, the better for production. Only when the pressure gradient is greater than the starting pressure gradient, fluid can flow. The phenomenon of desorption delays the propagation of pressure wave in coal seam. Therefore, the early development of coal bed methane (CBM) requires drainage slowly. The ultimate recovery of CBM can be improved by spreading the area of pressure propagation.