低渗透储层非线性渗流压力传播规律

Transmission of pressure in low permeability reservoir with non-linear seepage

低渗透油藏流体在地层中的流动一般表现出非达西渗流的特征,其在储层中的压力传播过程和压力分布规律与达西渗流明显不同.本文从分析开发中的不稳定渗流过程入手,建立了不同驱替压力梯度条件下的分段渗流数学模型,并采用稳定逐次逼近法,求解得到了拟线性渗流区与非线性渗流区的压力分布方程;基于实际油田开发情况,还系统地研究了在生产过程中非线性渗流条件下的压力传播规律,以及压力传播边界的压力分布规律,并对比分析了不同流动状态下的压力分布差别.研究表明:在生产过程中,随着压力波的向外传播,流体的流动由线性渗流转变为非线性渗流;而储层中的压力分布存在线性渗流分界点,且线性渗流分界点与井壁之间的距离随着压力波的传播先增大后减小,使得非线性流动区域不断增大.

Fluid flow in low permeability reservoir conforms to non-Darcy seepage,the distribution and transmission of pressure are obviously different in Darcy and non-Darcy seepage.This paper starts with the analysis of the process of unstable seepage in the oilfield development,and set up a multi-stage mathematic model,which in different pressure gradient is taken into accounted.A method of steady-state successive approach to unsteady-state solution is used to get the equation of the distribution of pressure in quasi-linear and non-linear seepage region in different condition of displacement pressure gradient.Based on oilfield cases,the transmission and distribution of pressure in the condition of non-linear seepage are studied systematically,besides,the difference of distribution of pressure in different flow state is analyzed.The analysis shows that,in the process of production,the flow of fluid is changed from the linear Darcy flow to the non-linear seepage flow;In the condition of non-linear seepage,there is a linear seepage demarcation point,and the distance between borehole wall and linear seepage demarcation point increases to the maximum and then starts to decrease,while the non-linear seepage region increases with the transmission of pressure.