Evaluating the Potential of Zwitterionic Surfactants for Enhanced Oil Recovery: Effect of Headgroups and Unsaturation

Surfactants increase the capillary number and resultantly pore-scale displacement efficiency by lowering interfacial tension (IFT) and changing wettability of the rock. However, conventional surfactants precipitate under harsh reservoir conditions such as high temperature and high salinity, thereby limiting their efficiency for oil recovery. As compared to other surfactants, zwitterionic surfactants have good salinity and thermal tolerance. In this work, six in-house developed zwitterionic surfactants with sterling thermal and salinity tolerance were investigated for their behavior at the oleic-aqueous interface. The IFT behavior was investigated by varying the hydrophilic headgroups and the degree of unsaturation in the hydrophobic tail of the surfactants. Additionally, the wettability alteration behavior of the surfactants was evaluated at elevated temperature and pressure. Experimental results depict that the synthesized betaine-type surfactants demonstrated exemplary stability and efficiency for EOR. The surfactants reduced the IFT at the oleic-aqueous interface and changed the wettability of carbonate porous media toward aqueous-wetting conditions. The surfactant headgroup influenced wettability alteration behavior in the order hydroxysulfonate > sulfonate > carboxy group. Meanwhile, the introduction of unsaturation decreased the surfactant wettability alteration behavior. Finally, oil recovery results from the spontaneous imbibition experiment on carbonates depict that the zwitterionic surfactants recovered 31.3-44.1% OOIP.