Studies on interfacial tensions of betaine and anionic-nonionic surfactant mixed solutions

Betaines and anionic-nonionic surfactants are suitable for applying in enhanced oil recovery (EOR) in the high-temperature and high-salinity reservoir conditions. We have used the spinning drop method to investigate the interfacial tension (IFT) values of alkyl carboxylicbetaine (ACB) and five types of anionic-nonionic surfactant (C14E3C, C16E3C, C18E3C, C18E5C and C18E10C) with different ethylene oxide (EO) numbers and different alkyl chain lengths against hydrocarbons and crude oil. Thereafter, under the same conditions, the IFT values of ACB and anionic-nonionic surfactant mixed solutions have also been investigated. The experimental results exhibit that for achieving ultralow IFT the proper hydrophilic-lipophilic balance (HLB) is prerequisite, but the tightness of the adsorption film is the key factor, which is controlled by the consistency of the spaces occupied at the oil side and the water side of an interface. This mechanism is so called "size compatibility". The ultralow level IFTs have been reached during wider concentration ranges as the mixed systems against crude oil, which have not happened when the hydrocarbons are the oil phase. These phenomena demonstrate the strong synergistic effect among ACB, anionic-nonionic surfactant and natural surface-active materials, which is important for the development of high-temperature and high-salinity oil reservoirs. (C) 2020 Published by Elsevier B.V.