基于孔隙网络模型的非稳态两相渗流模拟研究

Simulation on unsteady two-phase seepage based on pore network model

为了解决微观驱油中存在的严重黏性指进问题,将动态网络模拟算法与非稳态渗流理论相结合,研究了多孔介质中的非稳态两相渗流机理和压力传播过程。在验证模拟方法可靠性的基础上,分析了非稳态两相渗流过程中流体渗流与压力传播的规律,得出了注入流体速度、不利黏性比、压力传播和渗透率梯度等因素对黏性指进的影响规律,进而得到抑制黏性指进的措施。研究结果表明:孔隙尺度渗流过程中,孔隙流体压力传播影响压力波及区域内流体黏滞力和毛细管压力之间的平衡,进而影响两相流体界面移动,因此在孔隙尺度渗流模型中,考虑压力传播是准确描述两相流体界面移动的重要前提。在此基础上,提出了抑制黏性指进的措施:①在渗透率梯度减小的方向上,压力传播速度逐渐降低,注入流体能够在压力波及范围内进行较为均匀地推进,从而有助于提高流体波及效率;②以较慢的注入速度和沿孔喉半径减小的方向注入驱替介质将能够有效地稳定驱替前缘,从而达到提高微观驱油效率的目的。

During microscopic displacement,serious viscous fingering is likely to happen.So,the unsteady two-phase seepage mechanisms and the pressure propagation in porous media were figured out via both dynamic network simulation algorithm and unsteady seepage theory.After the reliability of the simulation was verified,several fluid-seepage and pres⁃sure-propagation laws in the process of unsteady two-phase seepage were analyzed,and the influences of fluid injection rate,adverse viscosity ratio,pressure propagation,and permeability gradient on the viscous fingering were clarified.Further⁃more,some measures to inhibit viscous fingering were made so as to improve microscopic displacement efficiency.Results show that in the process of pore-scale seepage,the pressure propagation in pore fluid may affect the balance between vis⁃cous force and capillary force of fluid in a pressure sweep region,and then the migration of two-phase fluid contact.There⁃fore,introducing the pressure propagation in the pore-scale seepage model is an important premise to describe this migra⁃tion accurately.In addition,the measures include that(1)at one direction toward permeability-gradient decrease,with a gradual decrease of pressure-propagation speed,some injected fluid can advance uniformly in the pressure sweep region,so as to improve the fluid sweep efficiency;and(2)at another direction toward a decrease of pore-throat radius,keeping a lower injection rate and injecting displacement medium can stabilize the displacement front,so as to improve the micro⁃scopic displacement efficiency.