低渗透油藏孔喉细小、孔隙结构复杂,固液界面相互作用力很大,在靠近孔喉壁面处存在一层流体边界层,阻碍流体在孔喉中的流动。为研究流体边界层对低渗透油藏流体渗流特征的影响,以去离子水在半径分别为10.0,7.5和5.0μm的微圆管中流动的实验数据为基础,通过数据拟合分析,确定了流体流动速度、边界层厚度与压力梯度之间的关系。结果表明,由于流体边界层的存在,低压条件下,去离子水在不同半径微圆管中的流动偏离经典的达西流动规律,表现出非线性特征,且存在启动压力梯度;随着管径的降低,流动偏离达西渗流规律的程度增大,非线性越发明显;随压力梯度增加,流体边界层厚度呈指数规律递减,压力增大到一定程度后,趋于定值。运用不等径毛管束模型,给出低渗透油藏单相流体渗流公式。

A fluid boundary layer would impede the flow of fluid near the pore and the throat of the rock in the low-permeability reservoir because of the small size of pore-throat, the complex pore structures and the large solid-liquid interfacial force. In order to study the influence of the fluid boundary layer on the fluid flow in a low permeability reservoir, the relationships between the fluid flow rate, the boundary layer thickness and the pressure gradient are obtained through analysis and fitting data, based on the experimental results of deionized water flowing through microtubes of radii of 10.0, 7.5 and 5.0μm, respectively. It is indicated that, due to the existence of the fluid boundary layer, the flow of deionized water through microtubes with different radii deviates from the classical Darcy flow pattern and shows nonlinear characteristics with a threshold pressure gradient under low pressure conditions. The degree of deviation of the flow pattern from the law of Darcy flow increases and the nonlinearity of the flow becomes more significantly with the decrease of the tube diameter. The fluid boundary layer thickness decreases exponentially with the pressure gradient and tends to assume a stable value when the pressure gradient approaches a critical value. The formula for single-phase fluid seepaging in a low permeability reservoir is obtained based on the non-equivalent diameter capillary module.