Efficiency of a sulfobetaine-type surfactant on lowering IFT at crude oil–formation water interface

A hydroxyl sulfobetaine surfactant (SBET-16) was synthesized, and the dynamic interfacial tension (DIFT) between the surfactant solutions and three types of crude oil from Shengli Oilfield were measured. The results indicated that, for Gudao and Gudong heavy oil, SBET-16 was efficient in lowering the IFT in alkali-free conditions. The result showed that the betaine surfactant had potential utility for alkali-free combination flooding. To investigate how betaine decreases the IFT, the oil was cut by distillation. Based on cutting temperature, the three types of heavy oil were cut into four distillates: fraction 1 (<180 °C), fraction 2 (180–350 °C), fraction 3 (350–500 °C) and fraction 4 (>500 °C). The IFT between SBET-16 and the distillate oils of three Shengli crude oils was measured. The results showed that the interfacial properties between betaine and vacuum residue (fraction 4) of the three types of crude oil were poor. However, for other distillate oil, the IFT values decreased correspondingly with increasing acid numbers of distillate oil. The gas chromatographic (GC) analysis of the crude oil also showed that the interfacial properties between SBET-16 and the crude oil containing more isoalkane were much better than those containing more n-alkanes. The study can be used to guide the design of surfactants for alkali-free combination flooding.