The Mechanisms Of Interfacial Tension Reduction And Emulsification By Surfactant On Residual Oil

Surfactant flooding is one of the important methods for tertiary oil recovery.It is of great significance to clarify the start-up mechanism of different surfactant properties on residual oil and quantify its EOR efficiency for optimizing surfactant in actual reservoir.The interfacial tension,emulsifying performance,adsorption and wettability-changing ability of surfactants were evaluated by interfacial tension meter,emulsion stability analyzer,ultraviolet spectrophotometer and contact angle meter.Two kinds of surfactants,Sodium Oleate(SOL),whose interfacial tension reaches ultra-low level,and Sodium Dodecylbenzene Sulfonate(SDBS)which can rapidly emulsify and have similar adsorption and wetting reversion ability with SOL were selected.The designed hydrophilic structural simulation model and dimension simulation model were used to carry out micro displacement experiment.The starting-up of different residual oil after water flooding and surfactant flooding with different production parameters were observed and quantitatively analyzed by optical microscope.The mechanism and recovery effect of interfacial tension and emulsification on different kinds of residual oil were analyzed.The results show that the main kinds of residual oil after water flooding are clustered,columnar,blind-end and island residual oil,and water flooding has little effect on the recovery of blind end residual oil.At low velocity,the total amount of residual oil in the small pore model is 30% higher than that in the pore model,which is mainly due to the cluster and blindend residual oil.However,the residual oil content in the macropore model is higher at high velocity,which is mainly due to the cluster residual oil.Both SOL system and SDBS system have excellent oil displacement performance.Among them,SOL system can effectively start all kinds of residual oil,and its effect on macropore model is more significant,which can enhance oil recovery by 3%-5%,mainly starting island and cluster residual oil.In SDBS system,the EOR effect of small pore model at low speed is 37% higher than that of large pore model,which mainly starts cluster residual oil.While at high injection speed,it is 2% lower,due to cluster and columnar residual oil.In addition,SDBS system has higher oil recovery than SOL system when injection volume is small,which indicates that emulsion system has better economic effect.After extreme water flooding,the recovery of SDBS in small pore model is40% higher than that of SOL.In the case of non-limit water flooding,the oil recovery of SOL system is higher than that of SDBS system only after high injection volume water flooding in macrospore models.Due to the Marangoni Effect,low interfacial tension system is easy to penetrate into the interface layer between oil and solid wall,peel off the oil from solid wall,and start up columnar and cluster residual oil.In addition,the blind-end residual oil can be elongated and deformed by one side infiltration.SDBS system transforms cluster residual oil into emulsion droplets and starts by emulsion carrying.The pressure fluctuation when the emulsion droplet passes through the throat makes the columnar residual oil extruded.The island residual oil is coalescence as columnar residual oil or squeeze out.