低渗透油藏毛细管压力动态效应的数值模拟研究

Numerical research on dynamic effect of capillary pressure in low permeability reservoirs

实验分析和理论研究表明毛细管压力存在动态效应,即其与润湿相流体的饱和度变化率相关,已有的物理实验表明低渗透油藏中的毛细管压力动态效应对于油气渗流存在着较大的影响。该文首先根据23个低渗岩心渗流曲线的数值拟合分析结果,建立了各项物理意义明确的非线性渗流运动方程,然后通过构造三种不同的饱和度变化速率的润湿相流体饱和度时变曲线,利用有限元数值方法模拟了三种饱和度曲线对应下的一维水驱油过程,并在完全基于数学方法较少依赖于物理实验的基础上计算了毛细管压力曲线。数值模拟的结果表明,低渗透油藏中存在较为明显的毛细管压力动态效应,且动态系数与介质的固有渗透率负相关,与润湿相流体的黏滞系数正相关。并通过与达西线性渗流模拟结果的对比表明了低渗油藏中非线性渗流产生的毛细管压力动态效应更为明显,动态系数也更大。

Physical experiments and theoretical analysis indicate that the capillary pressure is not only related to saturation of the wetting phase, but also to the time derivative, which is called dynamic effects. And the previous research shows that the porous flow process is effected by the dynamic effect in low permeability reservoirs. Based on the fitting analysis results of thev- p curves of 23samples, a nonlinear moving equation of porous flow is obtained. Three different saturation curves varying by time is introduced, and corresponding to which three FEM numerical simulations of physical process of 1D water drive displacement and the calculation of capillary pressure are accomplished. The FEM numerical results show relatively visible dynamic effects of capillary pressure in low permeability reservoirs. There is a negative correlation between dynamic coefficients and the intrinsic permeability, and a positive correlation between dynamic coefficients and the viscosity of wetting phase. The comparison results between the Darcy and the nonlinear porous flow indicate that the dynamic effects of capillary pressure in the low permeability reservoirs are more obviously and significant.