Study On Spontaneous Emulsification Flooding System For Low Permeability Reservoirs

Low permeability reservoirs have become an important development direction for our country to increase oil/gas production and ensure energy security.However,due to several problems like poor physical properties,small pores and throats,large capillary force,and strong Jiamin effect,the oil recovery efficiency is low for the conventional water flooding process.Surfactant flooding is one of the effective ways to reduce the residual oil.The formation,stabilization and migration of the emulsions in a reservoir can play a crucial role in improving the microscopic oil displacement efficiency and enlarging the macroscopic sweeping volume.Since a spontaneous emulsification method can significantly enhance the emulsification performance and generate adjustable emulsion droplets under very low or even without external energy.Therefore,we proposed a flooding method which could produce the fast spontaneous emulsification of crude oil.The method could spontaneously emulsify the crude oil under the flow in the porous medium of formation,and form the emulsion droplets with smaller size compared to the relative porous medium.Thus,the remaining oil could be effectively started and displaced.Firstly,a green anionic alkyl polyglucoside surfactant(APGSHS)with high surface(interfacial)activity was synthesized.Its structure and physicochemical properties were subsequently characterized.Secondly,APGSHS was combined with conventional cationic,anionic and zwitterionic surfactants to produce a spontaneous emulsification system with ultra-low oil/water interfacial tension,which consisted of 3000 mg/L APGSHS/CTAB anionic/cationic surfactant with a molar ratio of 6:4.The system could fast spontaneously emulsify the crude oil and form emulsion droplets with an average particle size of 0.2 ?m by bottom-up the bottle once,and the distribution of droplets size was relatively uniform.Then,the dynamic light scattering(DLS),static multiple light scattering(S-MLS)and three-phase rheology methods were used to study the performance and mechanism of spontaneous emulsification.Afterwards,by changing the concentrations,combined molar ratios and symmetry of the combined structures,the influence and synergetic mechanism of the ultra-low interfacial tension behaviors from the spontaneous emulsification system were explored.The results showed that the APGSHS/CTAB system,with appropriate anionic and cationic surfactant structure asymmetry,could exhibit good water-solubility and produce ultra-low oil/water interfacial tension in large concentration and combined molar ratio ranges.Notably,the combined system possessed an optimal structural parameter.Moreover,the salt-tolerance capacities of the system were studied,and the formation mechanism of the ultra-low interfacial tension of the spontaneous emulsification system was analyzed by several micellar models and theoretical calculation methods.The low permeability core flooding experiments showed that the optimal spontaneous emulsification flooding system could effectively start the remaining oil after water flooding process,and further improve the oil recovery efficiency by 11.95%?14.14%of the initial oil in place(IOIP).The spontaneous emulsification flooding system could effectively displace the remaining oil in the porous medium through the ultra-low interfacial tension and fast spontaneous emulsification mechanisms,with the interfacial disturbance and shearing action during the flow process.These results provided theoretical basis and technical support for the development and application of new technologies for improving water flooding efficiency and enhancing oil recovery in low permeability reservoirs.