Rheological behavior of a wormlike micelle and an amphiphilic polymer combination for enhanced oil recovery

Amphiphilic polymers have been widely studied and applied in oil fields as effective enhanced oil recovery (EOR) agents. However, the viscosity of their aqueous solution is low at low concentration. In order to improve their poor viscosity-thickening ability at low concentrations, a combined system was used by mixing a zwitterionic surfactant (erucyl dimethyl amidopropyl betaine, EDAB) and an amphiphilic polymer (APC16) at the mass ratio of 2:1. The rheological properties and aggregate microstructure of the EDAB–APC16 combination system were investigated by rheometry, scanning electron microscopy, transmission electron microscopy, and fluorescence spectroscopy, and the EOR efficiency was measured using core flood tests. The results showed that EDAB can significantly increase the viscosity of the APC16 solution, even though the polymer concentration is lower than its critical aggregation concentration. In the EDAB–APC16 combination system, the wormlike micelles of EDAB can synergistically interact with APC16 through hydrophobic association and electrostatic attraction to achieve a thickening effect. Furthermore, the effects of temperature, pH, and the inorganic salts on the viscoelasticity of the EDAB–APC16 system were investigated. An optimized EDAB–APC16 system at 1500 mg/l [pH = 7.5 and c (NaCl) = 5000 mg/l] was selected to be the oil displacing agent, which achieved an EOR of 18.4% after the initial water flood. The polymer–surfactant composite system under development exhibited great potential as an effective chemical EOR agent.