Research On Formation And Oil Displacement Performance Of Nano-emulsion System

The low permeability sandstone reservoirs possess the characteristics of poor physical property,strong heterogeneity and tiny pore throats,leading to the problems such as high injection pressure,rapid water-cut rising and low recovery efficiency in waterflood development.Aiming at the deficiency of traditional operation,a nano-emulsion is prepared and evaluated,for the purpose of enhancing oil recovery and reducing injection pressure in low permeability sandstone reservoirs.Firstly the improved method HLB-PTS method are implemented on screening the emulsifiers including surfactants and cosurfactants to synthesize the homogeneous bicontinuous microemulsion.Oil-in-water nano-emulsion is then formed through microemulsion dilution method.The stability mechanism and influencing factors of microemulsion and nano-emulsion are explored.Nano-emulsion properties,e.g.the electrical conductivity,the interfacial tension（IFT）,the ability of altering the rock wettability,the particle size and the microstructure are analyzed.Finally,the displacement efficiency of nano-emulsion is evaluated by corefloods and spontaneous imbibition experiments in sandstone.And the action mechanisms of nano-emulsion are also analyzed.Through the research above,micro-emulsion,that includes 37wt%a mixture of emulsifiers SJW-511（SDS:JFC:n-pentyl alcohol=5:6:11）,21wt%organic solvent（d-Limonene）and42wt%the Na Cl solution（0.12 mol/L Na Cl）is synthesized.Different kinds of nano-emulsion are obtained by diluting the microemulsion to different proportions.It turns out that both the microemulsion and nano-emulsion are transparent and homogeneous.The characteristics experiment shows that the nano-emulsion,which is initially prepared as a kind of homogeneous bicontinuous microemulsion,possesses the nanoscale particle size,ranging from 80-110 nm.This size allows the nano-emulsion to enter the tiny pores of low permeability reservoirs.The interfacial tension measurements show that the oil/nano-emulsion interfacial tension drops down to 3×10^-3 m N/m,which is in the range of ultra-low interfacial tension.In addition,result shows that the nano-emulsion alters the rock wettability from oil wet to water wet.Experimental observations in imbibition test and corefloods demonstrate that nano-emulsion,following water and surfactant floods,can effectively improve the tertiary oil recovery by about 28%,and reduce the injection pressure by 10%compared to the waterfloods.