超低渗透油藏非线性不稳定渗流特征研究

启动压力梯度和介质变形是油气在低渗透储层中渗流规律偏离达西定律的主要原因。基于超低渗透岩心非线性渗流实验,建立了在低速情况下渗流定律数学模型和同时考虑启动压力梯度及介质变形的超低渗透油藏非线性不稳定渗流数学模型。由于不稳定渗流数学模型的解法复杂,主要原因是控制方程具有强烈的非线性,同时流体流动边界也会随时间的变化而发生改变。为简化计算,在前人研究基础之上利用油藏压力分布近似表达式,研究了超低渗透油藏非线性不稳定渗流压力分布特征,并讨论了不同非线性因素对不稳定渗流的影响结果。

The Study on Characterization of Non-Linear unstable Flow in Ultra-low-Permeability Reservoirs

Non-linear seepage flow is caused chiefly by medium deformation and threshold pressure gradient (TPG) in low and ultra-low permeability reservoirs. Based on low-permeability laboratory experiment on non-linear flow, the mathematical models of single-phase non-linear steady flow are set up in consideration of medium deformation and TPG. Furthermore, corresponding mathematical solutions are put forward, and analysis of influencing on influential factors shows that: In the non-linear flow, the pressure and rate of yield decrease at the same radius as the minimum pressure gradient increases; Pressure of formations with the same minimum starting pressure gradient decreases as flow exhibits greater non-linearity while the rate of yield decreases; As the stress-sensitive coefficient gets larger, the formation pressure holding the same radius is also higher, and so is the average pressure.