Experimental Study On Viscosity Reducing By Emulsifying For Enhancing Heavy Oil Recovery

China has rich heavy oil reserves and has huge exploitation potential.Heavy oil has high viscosity and poor fluidity.Due to the great difference in water-oil mobility ratio during water flooding,the viscous fingering phenomenon is serious and the sweep coefficient is small.It has long-term strategic significance to overcome the technical problems and develop heavy oil resources efficiently.Viscosity Reducing by Emulsifying composite flooding is a potential method to improve oil recovery.The principle is to make heavy oil form O/W emulsion under the action of surfactant.It can reduce flow resistance of oil phase,improve fluidity and producing degree by reducing the viscosity of heavy oil.Aiming at conditions of ordinary heavy oil reservoirs,with viscosity reducing by emulsifying composite system and two conventional ultra-low interfacial tension composite systems as an example,this paper investigated viscosity reducing by emulsifying composite system Oil and water injection in same time seepage characteristics and the capability of enhanced recovery,and made comparison with two ultra-low interfacial tension composite systems.The apparent viscosity,interfacial tension and emulsification properties of the composite system were studied by laboratory evaluation.The results showed that the surfactant systems with ultra-low interfacial tension and its binary composite systems(SP)were easier to emulsify heavy oil,but its emulsion stability was poor.Viscosity reducing by emulsifying system with higher interfacial tension was difficult to emulsify heavy oil,but its emulsion was more stable.It indicated that there was no correlation between emulsion stability and ultra-low interfacial tension.Viscosity reducing by emulsifying characteristics of different oil displacement systems were studied by water and oil injection seepage experiment in porous media.The results showed that viscosity reducing by emulsifying system could significantly reduce the flow resistance and improve fluidity of heavy oil in porous media,while the conventional ultra-low interfacial tension flooding system had no similar effect.Based on the emulsifying properties of different oil displacement systems,it was considered that emulsion stability was the key to improve the fluidity of heavy oil through emulsification.The oil displacement tests under homogeneous conditions showed that the viscosity reducing by emulsifying composite system could increase oil recovery 15.6% OOIP,which was significantly higher than ultra-low interfacial tension composite systems(about 10.0%).This indicated that emulsion stability and viscosity reduction by emulsifying ability played an important role in the displacement of common heavy oil by binary compound flooding system.However,the choice of system was related to the viscosity of oil.When the oil viscosity was 60 m Pa·s,the two systems have similar effect in improving oil recovery.Under heterogeneous conditions,the viscosity reducing by emulsifying composite system could improve the fluidity of heavy oil in low-permeability sand pack and the water-oil mobility ratio.It had a larger oil recovery increase compared with the ultra-low interfacial tension composite system.The results of injection parameter optimization in homogeneous model show that,considering economic benefit and oil displacement efficiency,the optimum injection concentration,volume and rate were determined to be 3000 mg/L,0.3 PV-0.5 PV and0.25 m L/min by optimization of laboratory experiments.In this condition,it had good viscosity reducing by emulsifying effect and relatively high oil recovery increasing value(15.6%-18.5%).