Characterization of rock-fluid and fluid-fluid interactions in presence of a family of synthesized zwitterionic surfactants for application in enhanced oil recovery

Zwitterionic surfactants are gaining importance for their application in enhanced oil recovery (EOR) because of their favourable thermodynamic and surface properties. A family of carboxybetaine based surfactants with hydrophobic tail length of 12, 14, 16 and 18 carbons were synthesized and characterized by FTIR and H-1 NMR spectroscopy. Critical micelle concentration (CMC) of the surfactants were found to be very low as compared to the conventional surfactants and thermodynamic studies revealed better surface and micellization activity. Salt tolerance study and Krafft point analysis indicated the suitability of the surfactants in the harsh reservoir conditions. Reduction of interfacial tension (IFT) between crude oil and surfactant solutions significantly decreased with increase in carbon chain length. Presence of salt and alkali were found to have synergetic effect in IFT reduction by the surfactants. Phase behaviour study showed formation of Winsor type III microemulsion which is desirable to displace the trapped oil by miscibility mechanism. The surfactants were also found to be effective in altering the wettability of oil-wet rock to water-wet, resulting better oil recovery. Sand pack experiments showed an additional oil recovery of 30.82% of original oil in place (OOIP) by injection of a small pore volume of surfactant slug in combination with alkali and polymer.