| The demand for petroleum,as an important energy source,is increasing year by year.It is crucial to enhance oil recovery while increasing the intensity of exploration and development.As a new oil displacing agent,nano silica fluid has great application potential in improving oil recovery.However,the current research mainly focuses on the ability of nan silica to reduce the oil-water interfacial tension and its macroscopic oil displacement evaluation,lacking research on the interfacial adsorption mechanism of nano silica and the mechanism of oil droplet stripping and the migration characteristics of nanoparticles after stripping.The nano silica flooding technology has many uncertainties,which limits its application and promotion.Therefore,it is important to study the interfacial adsorption behavior of nano silica and establish the mechanism of nano silica on oil droplets stripping and migration.In this study,a nano silica system with interfacial activity was prepared by physical modification.The oil-water interfacial adsorption behavior and solid-liquid interfacial adsorption behavior of active nano silica was studied by using interface rheometer,molecular dynamics simulation and ultraviolet spectrophotometer.The oil droplet stripping mechanism was revealed by using nuclear magnetic resonance analysis and imaging technology analysis,combined with the performance of active nano silica.The three-dimensional microscopic pore throat model and optical microscopy system were used to study the rupture and coalescence behavior during oil droplet migration,and the migration characteristics of oil droplets in porous media were analyzed.The results showed that the DTAB molecules migrated along the surface of the nano silica particles to the contact between the nano silica particles and the oil phase when the active nano silica particles were adsorbed on the oil-water interface from the solution,forming a Janus structure.The active nano silica particles were closely arranged at the interface to form a solidlike film.When the concentration of DTAB increased,the concentration of nano silica particles at the interface increased,the distance between its mass center and oil-water interface were closer,the curvature of the interface decreased,the capillary force decreased and the swept volume increases during the displacement process.The active nano silica could reduce the oilwater interfacial tension to 19.55 m N/m,forming a wedge-shaped nanofluid film structure between the oil droplet and the core surface.The oil droplets were effectively stripped under the action of the structural separation pressure,improving the oil washing efficiency.The oil droplets loaded with nanoparticles were easily broken after interface being stretched when passing through the pore throat structure.Since the active nano silaca particles were hardly desorbable at the oil-water interface,the interface is difficult to shrink when the oil droplets coalesced.Therefore,the oil droplets could be recovered under smaller size after rupturing and pass through the subsequent pore structure with less flow resistance.The adsorption capacity of active nano silica on the surface of sandstone was 3.63 times than that of nano silica and its adsorption on the surface of sandstone could adjust the wettability of core surface to neutral water-wet.There were streaming around and fluid channeling phenomena in the hydrophilic and lipophilic reservoirs respectively and the recovery rate was low.The neutral water-wet reservoir had the highest recovery rate.Core flooding results showed that active nano silica flooding could increase oil recovery by 8.09% compared with water flooding. |
PDF Full Text Request