The structure effect on the surface and interfacial properties of zwitterionic sulfobetaine surfactants for enhanced oil recovery

Abstract

The surface and interfacial properties of five zwitterionic surfactants, including three propyl sulfobetaines CSB (where the carbon atom number of the alkyl chain is 12, 14 and 16, respectively) and two hydroxypropyl sulfobetaine surfactants CHSB (where the carbon atom number of the alkyl chain is 12 and 14, respectively), were studied at both air–water and oil–water interfaces. The surface activity of these surfactants at the air–water interface in aqueous solutions was investigated by the Wilhelmy plate method at 30 °C and ambient pressure. The values of the critical micelle concentration (CMC) and surface tension at CMC (γ_CMC) were determined from the surface tension measurements. The obtained results indicate that CMC and surface tension strongly depend on the surfactant molecular structure. An increase in the alkyl chain length results in a decrease in the CMC and γ_CMC values. The presence of a hydroxyl group causes an increase in CMC values and a decrease in γ_CMC values. The hydroxypropyl sulfobetaine surfactants have better surfacial properties. In addition, the interfacial activity at the oil–water interface among the crude oil–reservoir water–surfactant systems was investigated by use of the spinning drop method under harsh reservoir conditions of high temperature (90 °C) and high salinity (11.52 × 10⁴ ppm, including 7040 ppm Ca²⁺ and 614 ppm Mg²⁺). It is interesting that the transient minimum dynamic interfacial tension (DIT_min) could be observed in a specific concentration range. The time to reach DIT_min is different with different surfactant molecular structures and surfactant concentrations. The hydroxypropyl sulfobetaine surfactant C₁₄HSB shows excellent interfacial properties: it can reduce interfacial tension (IFT) between oil and water to an ultralow level at a very low concentration, and the ultralow IFT phenomenon only occurs in a specific concentration range from 0.03 to 0.10 wt%. In this work, hydroxypropyl sulfobetaine surfactants exhibit remarkable ability and are good candidates for chemical agents to enhance oil recovery in harsh reservoirs.