Study On The Spontaneous Emulsification Flooding System And Its Displacing Performance For Low Permeability Reservoir

For low permeability reservoirs,there are still a large amount of residual oil and remaining oil in the formation after conventional water flooding.Polymer flooding technology,which is widely applied in middle and high permeability layers,cannot be used in low permeability reservoirs due to high injection pressure.Therefore,a spontaneous emulsification system screening method based on oil/water interfacial tension and spontaneous emulsification evaluation was proposed in this paper.This method aimed at improving the stability of simulated O/W emulsion.Using the synergistic effect of emulsifier,alkali and conventional surfactant,the optimized formula of spontaneous emulsification system for Dagang crude oil is composed of 4000 mg/L(APG1214:HABS=7:3)+ 1000 mg/L NaOH(Referred to as AHN).The emulsification properties of the spontaneous systems and microscopic characteristics of the simulated O/W emulsions were characterized.Meanwhile,Turbiscan Lab Expert Stabilizer and Physica MCR301 Rheometer were employed to expound the mechanism of enhancing emulsification and emulsion stabilization of spontaneous emulsification system in this thesis.It is found that the alkali could in situ produce surface active substances by reacting with organic acid,which displays synergistic effect with other two surfactants.This would reduce the oil/water interfacial tension as well as enhance oil/water interfacial strength.Thereby the rate of coalescence of oil droplets and floating are weakened,so as to enhance the emulsion stability.The EOR efficiency of spontaneous emulsification flooding systems after water flooding was identified.The spontaneous flooding systems could significantly enhance the crude oil recovery efficiency in both middle and low permeability cores.The mechanism of displacing residual oil by spontaneous emulsification system in low permeability reservoir is proposed.Residual oil saturation in the formation could be reduced using spontaneous emulsification flooding system.As the spontaneous emulsification system could reduce the interfacial tension and show interfacial "pulling" and "squeezing" oil effect,crude oil will be spontaneously emulsified into small oil droplets and flood without capillary force.Thereby,the oil recovery is significantly improved.