Emulsification Of Crude Oil By Surfactants And Its Role In Enhancing Oil Recovery

Emulsification is one of important mechanisms of EOR in surfactant flooding,given increasing importance in recent years.Taking Sha second 2+3 block in west of Pucheng oilfield as an example,emulsification of surfactants and its role in EOR are studied in the paper.The two surfactants YD-1 and SHY-1 suitable for this block were selected.The two surfactants have similar ability of reducing interfacial tension,adsorptive property and performance of changing wettability,but different emulsifying behavior.The emulsifying power of YD-1 is much higher than that of SHY-1.YD-1 could emulsify oil more easily than SHY-1 under low emulsification strength.The emulsion of YD-1 developed under high emulsification strength is relatively stable,while that of SHY-1 separates water soon and demulsifies.The emulsification of YD-1 is much higher than that of SHY-1.The surfactants both have high oil washing efficiency in low concentration,YD-1 relatively higher.During the simultaneous injection of oil and surfactant solution,the pressure and produced liquid are observed to determine whether the surfactants emulsify the oil or not.The critical emulsification speed is defined as the minimum flow rate at which oil could be emulsified by surfactant in the porous media.The critical emulsification speed of 0.5% YD-1 and oil is 0.25 mL/min,while that of SHY-1 is higher than 1 mL/min.In homogeneous porous media,the plugging performance of emulsion developed by shearing in the porous media is evaluated.The plugging performance is better with the more emulsion injected,the bigger oil volume fraction and the lower permeability of target formation.When the injection is higher than 0.5 PV,the oil volume fraction is larger than 10% and the permeability of target formation is lower than 1μm2,the emulsion could block off the target formation,increases injection pressure enormously.In heterogeneous porous media,the emulsion developed by shearing in the porous media could reduce the fractional flow of the high permeability sand pack.the bigger of the permeability contrast,the worse the profile control effect.When the emulsion injection is 0.5 PV,profile control is favorable in the formation whose permeability is about 2,while bad in the formation whose permeability is about 5.The oil displacement experiments shows YD-1 with fine emulsifying capability could emulsify the oil.The emulsion developed during oil displacement has mobility control ability,could increase injection pressure and expand sweep efficiency.No matter in the homogeneous and heterogeneous porous media,YD-1 flooding could improve 5%OIIP more,compared with SHY-1,which has similar interfacial tension,worse emulsifying capability.