Studying the factors determining the ultralow interfacial tensions of betaine solutions against crude oil

Betaine surfactants reduce oil-water interfacial tension (IFT) to an ultralow level through the synergistic effects between the surfactants and the active components of crude oil. These surfactants exhibit potential for applications in chemical flooding. However, the synergistic effect is affected by the structure of betaine and the properties of the aqueous phase. In this study, the dynamic and equilibrium IFTs of a series of betaine surfactant solutions against crude oil were measured under different aqueous phase conditions. The results indicate that the sizes of the hydrophobic and hydrophilic groups of betaine considerably affect its ability to reduce the IFT against crude oil. In addition, the weak base sodium bicarbonate (NaHCO3) in formation water reacts with petroleum acid and considerably promotes the mixed adsorption of crude oil components at the interface. As a result, the synergistic effect of IFT reduction between betaine and crude oil is strongly enhanced. Therefore, betaine molecular size and aqueous -phase pH are two major factors affecting the synergistic effect between betaine and crude oil. This study provides theoretical and practical guidance for chemical flooding to achieve enhanced oil recovery.