Inhibition of viscous fingering phenomenon in porous media by nanoparticle surfactants
Two-phase flow in porous media is common in many natural and industrial processes,i.e.,oil displacement in underground porous 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,pore structure,and fluid viscosity.It is important to study the mechanism of flow regulation to improve the replacement efficiency.However,the interfacial instability of two-phase displacement in porous media can lead to the viscous fingering phenomenon.It is characterized by finger-like protrusions at the displacement interface,which may significantly decrease the two-phase displacement efficiency.Therefore,it is usually required to realize a stable displacement mode and avoiding the emergence of finger displacement mode in the practical application process.Recently,it has been demonstrated that nanoparticles dispersed in water and end-functionalized polymers in oil can react at the oil-water interface to form nanoparticle surfactants.These surfactants can significantly reduce the water-oil interfacial tension and induce interfacial viscoelasticity.Therefore,in this study,a new method is proposed to inhibit viscous fingering in porous media by using nanoparticle surfactants.A microfluidic visualization system was established to explore the influence of nanoparticle surfactants on the interfacial stability of water-oil two-phase flow in porous media.The interfacial dynamical properties with the addition of different displacement agents were investigated,i.e.,nanoparticles alone,polymers alone,and nanoparticle surfactants.It is demonstrated that nanoparticle surfactants can effectively inhibit the viscous fingering phenomenon.Under the same conditions of fluid viscosities and interfacial tension,nanoparticle surfactants induce a higher fractal dimension and larger displacement efficiency compared to the case of pure water and oil.Besides,the effects of nanoparticle surfactant concentration on the interfacial dynamical properties were also investigated,and the underlying physical mechanisms of nanoparticle surfactants inhibiting the viscous fingering phenomenon were further explored.It was found that increasing the concentration of nanoparticle surfactants significantly enhances the interfacial stability of water-oil displacement in porous media with different structures,while the type of nanoparticle surfactants has little effect.The effect of nanoparticle surfactants on the interfacial tension properties of oil and water was analyzed,it is concluded that the elastic film generated by nanoparticle surfactants at the water-oil interface is the most important reason for the inhibition of viscous fingering.By analyzing the phase diagram of interfacial stability of water-oil displacement in porous media based on the capillary number and the viscosity ratio,the transformation boundaries of stable displacement and viscous fingering of nanoparticle surfactants displacement in porous media is obtaine.We found that nanoparticle surfactants substantially increase the critical capillary number and viscosity ratio required for viscous fingering to occur,and the inhibitory effect on viscous fingering was significant at different parameter ranges.This provides a theoretical basis for the oil-water interface regulation technology based on nanoparticle surfactants.
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