纳米颗粒表面活性剂对多孔介质中黏性指进现象的抑制

Inhibition of viscous fingering phenomenon in porous media by nanoparticle surfactants

多孔介质中不稳定的两相驱替会导致黏性指进现象,对实际工业中的两相流动过程产生不利影响.已有文献证明水相中的表面功能化纳米颗粒和油相中的功能化基团聚合物可以在油水界面发生反应生成纳米颗粒表面活性剂,降低界面张力并诱发界面黏弹性.本文提出使用纳米颗粒表面活性剂抑制多孔介质中黏性指进的新方法,通过微流体可视化实验,研究了纳米颗粒表面活性剂对多孔介质中驱替界面特性的影响规律.结果表明,纳米颗粒表面活性剂可以有效抑制多孔介质中的黏性指进现象,驱替效率对比纯水纯油提高了约2.5倍.通过分析基于不同毛细数与黏度比下的驱替模式分布相图,得到了多孔介质中纳米颗粒表面活性剂稳定驱替和黏性指进两种驱替模式的转变界限,证明纳米颗粒表面活性剂驱替对比纯水纯油大幅提高了黏性指进出现的临界毛细数和黏度比,在不同的参数范围内对黏性指进都有显著的抑制作用,为多孔介质中黏性指进的抑制提供了新的思路.

Two-phase flow in porous media is common in many natural and industrial processes,i.e.,oil displacement in undergroundporous media,where the competition and replacement between the invading and defending phases is crucial.In particular,the efficiency of two-phase displacement is governed by various factors,such as the two-phase interfacial tension,porestructure,and fluid viscosity.It is important to study the mechanism of flow regulation to improve the replacementefficiency.However,the interfacial instability of two-phase displacement in porous media can lead to the viscous fingeringphenomenon.It is characterized by finger-like protrusions at the displacement interface,which may significantly decreasethe two-phase displacement efficiency.Therefore,it is usually required to realize a stable displacement mode and avoidingthe emergence of finger displacement mode in the practical application process.Recently,it has been demonstrated thatnanoparticles dispersed in water and end-functionalized polymers in oil can react at the oil-water interface to formnanoparticle surfactants.These surfactants can significantly reduce the water-oil interfacial tension and induce interfacialviscoelasticity.Therefore,in this study,a new method is proposed to inhibit viscous fingering in porous media by usingnanoparticle surfactants.A microfluidic visualization system was established to explore the influence of nanoparticlesurfactants on the interfacial stability of water-oil two-phase flow in porous media.The interfacial dynamical propertieswith the addition of different displacement agents were investigated,i.e.,nanoparticles alone,polymers alone,andnanoparticle surfactants.It is demonstrated that nanoparticle surfactants can effectively inhibit the viscous fingeringphenomenon.Under the same conditions of fluid viscosities and interfacial tension,nanoparticle surfactants induce ahigher fractal dimension and larger displacement efficiency compared to the case of pure water and oil.Besides,the effectsof nanoparticle surfactant concentration on the interfacial dynamical properties were also investigated,and the underlyingphysical mechanisms of nanoparticle surfactants inhibiting the viscous fingering phenomenon were further explored.It wasfound that increasing the concentration of nanoparticle surfactants significantly enhances the interfacial stability of wateroildisplacement in porous media with different structures,while the type of nanoparticle surfactants has little effect.Theeffect of nanoparticle surfactants on the interfacial tension properties of oil and water was analyzed,it is concluded that theelastic film generated by nanoparticle surfactants at the water-oil interface is the most important reason for the inhibition ofviscous fingering.By analyzing the phase diagram of interfacial stability of water-oil displacement in porous media basedon the capillary number and the viscosity ratio,the transformation boundaries of stable displacement and viscous fingeringof nanoparticle surfactants displacement in porous media is obtaine.We found that nanoparticle surfactants substantiallyincrease the critical capillary number and viscosity ratio required for viscous fingering to occur,and the inhibitory effect onviscous fingering was significant at different parameter ranges.This provides a theoretical basis for the oil-water interfaceregulation technology based on nanoparticle surfactants.