Construction Of Ultra-low Interfacial Tension System And Oil Displacement Performance Evaluation In Changqing Low-permeability Reservoir

Low-permeability oil reservoirs are important resources for increasing reserves and production in China's petroleum industry for a long time to come.Surfactant flooding is a very effective method to improve the recovery of low-permeability reservoirs.However,the existing surfactants are difficult to promote and apply in the oil field due to the low interface activity and high cost.Gemini surfactants have highly effective interfacial activity and excellent synergistic effects.Hence,it has great application potential.Based on GAES,an anionic-nonionic gemini surfactant synthesized in the laboratory,an ultra-low interfacial tension flooding system was obtained by screening the types of surfactants,proportions and the dosage.The formation mechanism of the ultra-low interfacial tension system was analyzed.The emulsification properties of the system were evaluated.The effects of temperature and mineralization on the interfacial tension of the system were investigated.With the help of physical simulation oil displacement experiments,the oil displacement performance of the system was evaluated and the oil displacement mechanism was revealed.The results show that GAES can complex with stearyl trimethyl ammonium bromide(STAB)to form ultra-low interfacial tension with Changqing crude oil in a wide concentration range(100?1000 mg/L)and compound ratio(9: 1?5: 5).The formation mechanism of ultralow interfacial tension is related to the strong interaction between anionic and cationic surfactants.1000 mg/L GAES/STAB complex exhibits the best emulsification effect at a compounding ratio of 1: 1,and can form an easily emulsified and weakly stable emulsion.The results of physical simulation flooding experiments show that the GAES/STAB complex has the highest flooding efficiency of 18.67%,as well as the best effect of injection pressure reduction with the pressure reduction rate of 44.55%.The combined effect of ultra-low interfacial tension and emulsification effectively reduces residual oil saturation and improves oil displacement efficiency.The complex will provide a new way to enhance the oil recovery of low-permeability oil reservoirs.