盲端孔道内黏弹性聚合物驱油两相渗流规律

Two-phase Fluid Flow of Viscoelastic Polymer Flooding in Dead End Channels

已有的聚合物溶液单相渗流理论与实验研究均已证实聚合物的弹性特征能够扩大其在多孔介质内的波及效率。在黏弹性聚合物溶液单相渗流理论的基础上,针对黏弹性聚合物溶液、原油两相流动中弹性对两相渗流的作用机制问题,建立了黏弹性流体、牛顿流体的两相渗流控制方程,用VOF方法进行两相界面追踪,以Open FOAM为平台,运用有限体积法对控制方程组数值求解,研究了黏弹性聚合物溶液在盲端孔道内的流动规律。从饱和度分布、速度分布、驱替压差和第一法向应力差变化特征方面,揭示了黏弹性聚合物溶液的微观渗流机理。结果表明:随着松弛时间的增加,即聚合物溶液弹性的增大,两相界面向盲端内部扩展越深,驱油效率越高;当驱替时间达23. 0 s时,松弛时间为0. 100 s的聚合物溶液驱油效率,比松弛时间为0. 001、0. 010 s时分别高19. 0%、9. 2%;聚合物溶液的弹性越大,附加压降越大,其第一法向应力差也越大,在一定程度上可提高驱油效率。研究结果为油田三次采油聚合物驱油体系设计、筛选提供了重要理论支持,同时有益于丰富黏弹性聚合物溶液的驱油机理。

Both theoretical and experimental studies on single phase fluid flow of polymer solutions have proved that the elastic properties of polymers can increase their sweep efficiency in porous media. On the basis of single phase fluid flow theory of viscoelastic polymer solution, aiming at the active mechanism of elasticity to two-phase fluid flow in viscoelastic polymer solution and crude oil two-phase flow, the two-phase fluid flow control equation of viscoelastic fluid and Newtonian fluid was established, the VOF method was used to trace the two-phase interface, and the finite volume method was used to solve the numerical value of control equation set on the OpenFOAM platform to study the flow law of viscoelastic polymer solution in the dead end channel. The microscopic filtration mechanism of viscoelastic polymer solution was revealed from the behavior of saturation distribution, velocity distribution, displacement pressure difference and first normal stress difference. The study results show that with the increase of relaxation time, i.e., the increase of elasticity of polymer solution, the deeper the two-phase interface propagates into the dead end, the higher the oil displacement efficiency is;when the displacement time is up to 23.0 s, the oil displacement efficiency of polymer solution with relaxation time of 0.100 s is 19.0% and 9.2% higher than that of 0.001 s and 0.010 s respectively;the greater the elasticity of polymer solution, the greater the additional pressure drop, and the greater the first normal stress difference, which can improve the oil displacement efficiency to some extent. The study results provide important theoretical support for the design and screening of polymer flooding system in tertiary oil recovery of oilfield, and simultaneously are beneficial to the enrichment of oil displacement mechanism of viscoelastic polymer solution.