Screening of amphoteric and anionic surfactants for cEOR applications using a novel approach

Surfactants are used in chemical enhanced oil recovery (cEOR) to increase the capillary number by decreasing the oil/water interfacial tension (IFT). In this work, carboxybetaine based amphoteric and propoxylated anionic surfactants were evaluated for application in cEOR. Thermal stability of the surfactants was assessed using a novel approach based on FTIR, NMR and TGA analyses. The anionic surfactant showed lower initial IFT compared to the amphoteric surfactant. After aging at 90. °C for a period of 10 days, the amphoteric surfactant maintained its IFT, while almost two orders of magnitude increase in the IFT of the anionic surfactant was observed. TGA analysis showed that the two surfactants were thermally stable for short exposure times. For long term stability, both FTIR and NMR analyses showed structural changes in the aliphatic region after aging in the anionic surfactant. The thermally stable amphoteric surfactant was further evaluated at different concentrations, temperatures and salinity. By increasing the surfactant concentration, IFT decreased initially and then increased with the increase in surfactant concentration. The oil/water IFT decreased by adding salts and increased with the increase in temperature. The results of NMR, FTIR and TGA techniques showed good correlation with IFT measurements and showed the potential of using these techniques in screening surfactant.