New insights into the mechanism of surfactant enhanced oil recovery: Micellar solubilization and in-situ emulsification

Reducing the oil-water interfacial tension (IFT) to ultra-low is believed the primary mechanism for surfactant-based enhanced oil recovery (EOR) process. However, field trials have shown that low concentration surfactant flooding can also improve oil recovery without ultra-low IFT. To clarify the mechanism behind, the currently-used surfactant, naphthenic arylsulfonate (NAS), was used to unravel its function during surfactant flooding from the horizon of micron- and nano-scale. The solubilization capacity of NAS micelle to petroleum fractions was evaluated through light absorbance strategy, small-angle neutron scattering, dynamic light scattering and transmission electron microscopy. It was found that micellar solubilization plays a significant role during the surfactant flooding. In-situ emulsification was visualized in microfluidics with three types of microchips, respectively. A series of displacement tests were carried out with NAS solution pumping into oil-saturated chip. The results show that in-situ emulsification improve oil recovery mainly through blocking and entrainment effects. Results from this work aid in understanding the interaction between surfactant solution and petroleum fractions at low surfactant concentration, which is helpful for design surfactant-based displacing system for EOR process.