Research And Application Of Surfactant Flooding System With Low Interfacial Tension

In China,the technology of chemical flooding based on surfactant is the main method in the enhance of oil recovery.However,with the progress of oilfield development,the complex reservoir conditions and fluid characteristics lead to poor salt tolerant and cloud point in the use of anionic and non-ionic surfactants.The fatty alcohol polyoxyethylene ether sulfonate as a nonionic-anionic surfactant has the advantages of low and high interfacial tensions and high tolerant,became the most promising surfactant in EOR.In this paper,fatty alcohol polyoxyethylene ether?AEO?was used as raw material to synthesized fatty alcohol polyoxyethylene ether sulfonate?AESO?by olefin addition method through two steps:allylation and sulfonation.The reaction conditions was optimized by signal factor and orthogonal experiment.In the allylation reaction,PEG-600 was used as the phase transfer catalyst,the reaction temperature was 120°C,the reaction time was 7h and the molar ratio of allyl chloride and polyoxyethylene ether was 1.8.In the sulfonation reaction,sodium nitrate was used as the catalyst,the reaction temperature was 100°C,the reaction time was 9h and the sulfonating agent to allyl polyoxyethylene ether molar ratio was 1.9.A series of fatty alcohol polyoxyethylene ether sulfonate surfactants with different oxyethylene groups were synthesized according to the above optimized conditions,the properties of different oxyethylene vinyl alcohol ethoxylates were compared and the effect of the number of oxyethylene groups on the interfacial tension of the surfactant was discussed.It founds that with the number of oxyethylene groups increasing,the surface and interfacial tension shows a“V”shape curve.AESO-6 has the best performance:the critical micelle concentration was 0.049mmol/L and the interfacial tension was 6.03×10^-2mN/m.Research was carried out on the mixed surfactant system of the fatty alcohol polyoxyethylene ether sulfonate and the common surfactant.A surfactant displacement system with a mass concentration of 0.3%was selected,which made up of fatty alcohol polyoxyethylene ether sulfonate and petroleum sulfonate by 1:3.The surfactant displacement system can reduce interfacial tension to 10^-3mN/m under the condition of different temperature and stability.Simulated oil displacement test shows that the mixed surfactant flooding can enhance oil recovery efficiency by more than 7%based on water flooding efficiency.Based on the results of laboratory research,pilot test of surfactant flooding was carried out in Yanchang oilfield,the daily oil production of well group increased by 1.26t and total water cut decreased by 0.9%.It provides a strong theoretical and practical basis for the application of this technology in low permeability oilfield.