考虑二次梯度项及动边界的双重介质低渗透油藏流动分析

Flow Analysis of Fluid in Low Permeability Reservoir with Double Porosity Including Effects of Quadratic Gradient Term and Moving Boundary

在传统试井模型的非线性偏微分方程中根据弱可压缩流体的假设,忽略了二次梯度项,对于低渗透油藏这种方法是有疑问的。低渗透问题一个显著的特点就是流体的流动边界随着时间不断向外扩展。为了更好地研究双重介质低渗透油藏中流体的流动问题,考虑了二次梯度项及活动边界的影响,同时考虑了低渗透油藏的非达西渗流特征,建立了双重介质低渗透油藏流动模型。采用Douglas-Jones预估-校正差分方法获得了无限大地层定产量生产时模型的数值解,分别讨论了不同参数变化时压力的变化规律及活动边界随时间的传播规律,还分析了考虑和忽略二次梯度项影响时模型数值解之间的差异随时间的变化规律,做出了典型压力曲线图版,这些结果可用于实际试井分析。

According to the assumption of slightly compressible fluid, the quadratic gradient term in non- linear partial differential equation of the traditional well test models for liquid flow is usually neglected. This method is questionable for low permeability reservoirs. The fluid flowing boundary extends outwards continuously with time is the remarkable feature of low permeability reservoirs. Here, to study the flow problem better, not only the influence of the quadratic gradient term and moving boundary, but also the characteristic of non-Darcy flow in low permeability reservoir were considered for the flow system of low permeability reservoir with double porosity. The flow model of double porosity in low permeability reservoir was built. The numerical solution of the flow model was obtained by Douglas-Jones predictor corrector method at a constant rate production for an infinitely large system. The changing rules of pressure when various parameters change and the moving rule of the moving boundary were addressed. The changing rule of the difference between the pressure solution of traditional model and the new model considering the quadratic gradient term was analyzed. The plots of typical pressure curves were given, and the results can be applied to well test analysis.