Modification Of Nano-SiO₂ Particles To Change Rock Wettability And Oil Displacement Effect

The pore throat in the matrix of low permeability reservoir is micro nano level,with large specific surface area.It is difficult to inject conventional oil displacement agent and the adsorption loss is too large,which makes the remaining oil difficult to use.Nano materials are easy to be injected into the reservoir because of their particle size matching with the low permeability pore roar,which can basically achieve the whole reservoir sweep and greatly improve the recovery rate.However,because of its huge surface energy,the common nanoparticles are not stable and easy to agglomerate due to the changes of the formation environment,blocking the pore throat channel and causing reservoir damage.And,the current research focuses on the application of nanoparticles in oil displacement,there are few studies on the change of wettability of lipophilic solid surface.In this paper,a kind of modified nano silica particles with amphiphilic structure is used as the nano oil displacement agent to enhance oil recovery in low permeability reservoir,and its wettability and oil displacement effect are systematically studied.The physicochemical properties and interfacial tension of the modified nano silica particles were characterized by FTIR,SEM,particle size analyzer and rotary drop interfacial tension meter;the concentration,temperature,metal ion concentration and mineralization parameters of the nano silica particles were changed;the influence of different factors on the dispersion stability was studied by measuring zeta potential of the nano solution;the ability of nano particles to change the wettability of solid surface is analyzed by measuring contact angle,and the influencing factors are studied;the core physical model is used to compare the wettability and recovery degree of core before and after displacement,and the injection parameters and permeability applicable limits of nano solution are optimized.The experimental results show that the modified nano silica particles have good sphericity and monodispersity,the average particle size is 50 nm,and the 0.1wt%modified nano particles reduce the interfacial tension between oil and water from42m N/m to 0.31m N/m;the results of zeta potential test showed that the stability of nano solution was good between 25?and 55?,and decreased with the increase of Na⁺,Ca²⁺,salinity;the stability of nano solution is the best under the condition of strong acid or strong base;the modified nano silica particles have good ability to change the wettability of lipophilic solid surface,which can change the lipophilic surface into a hydrophilic surface with the best concentration of 0.1wt%;the increase of temperature has no obvious effect on the ability of the nano particles to change the wettability of the lipophilic solid surface;strong acid,strong alkali,high salinity and monovalent and divalent metal ions make the hydrophobic quartz surface become strong hydrophilic;in the oil displacement experiment,the modified nanoparticles can greatly improve the oil recovery of low permeability core,and the wettability of core surface changes to hydrophilic before and after displacement;the optimal results of core injection parameters are as follows:nano-particle concentration 0.1wt%,injection rate0.1m L/min,injection volume 0.5PV,core permeability between 5×10^-3?m²and22×10^-3?m²,and enhanced oil recovery is between 25.53%and 28.74%;the amphiphilic structure of modified nano silica particles can change the wettability of the surface of the amphiphilic solid and greatly improve the recovery of low permeability reservoir,which has great potential for field application.