Rheology and microstructure of zwitterionic-anionic surfactant for enhanced oil recovery

Abstract Surfactants have been widely used in enhanced oil recovery. The zwitterionic surfactant possesses a high critical micelle concentration, that its use requires an increased concentration and thus it is uneconomical. In this paper the use of erucic acid amidopropyl- betaine (EDAB, C22) and sodium alkyl sulfate (SDS) is proposed to construct a worm-like micelle with mass ratio of 1.5:1. The viscoelasticity and the structural morphology of worm-like micelle systems were studied using cryo-transmission electron microscopy, dynamic light scattering (DLS) and rheology. The results showed that EDAB/SDS with a mass concentration of 0.3% (0.18% EDAB + 0.12% SDS) exhibited viscoelastic fluid behavior when the pH value was 9.15 at 43 °C. The shear viscosity of the EDAB/SDS system is greater than that of the EDAB system. It shows that longer linear worm-like micelle and larger entangled three-dimensional network structure are formed in the EDAB/SDS system. The rheological properties EDAB/SDS system are affected by pH, temperature and inorganic salts. The viscoelasticity of the EDAB/SDS system increases first and then decreases with the increase of temperature and NaCl concentration. The electrostatic interaction between EDAB and SDS can be adjusted by changing the pH value to affect the aggregation behavior of worm-like micelle molecules. Worm-like micelles continue to grow longitudinally with the increase of pH value and form larger aggregate structures, which are manifested by an increase in viscosity.