Efficacy of f-MWCNT-CTAB nano-complex in low-salinity seawater EOR operation

Nanoparticles (NPs) of various types have gained attention for utilization in chemical enhanced oil recovery (CEOR) studies. This is because they can potentially take part in interfacial interactions due to their tiny size and unique characteristics, which would otherwise lead to more efficient EOR operations. Among various NPs, multi-walled carbon nanotubes (MWCNTs), due to functionalization capability, the abundance of carbon sources, and reasonable price, could be a promising option. In this study, a novel nano-complex was synthesized based on the surface modification of the functionalized MWCNTs (f-MWCNTs) with cetyltrimethylammonium bromide (CTAB). The synthesized f-MWCNT-CTAB nano-complex was then used, for the first time, in low salinity (12-fold diluted) seawater (LSSW) to discern interfacial interactions between LSSW and crude oil/dolomite. The results showed great potential of the nano-complex to reduce the crude oil/brine interfacial tension (IFT). Accordingly, the critical micelle concentration (CMC) of the nano-complex in the LSSW/crude oil interface was obtained to be 20 ppm of the nano-complex, for which a low IFT value of 0.33 mN/m was recorded. Moreover, despite the low adsorption of nano-complex on the dolomite surface, a profound wettability alteration of the dolomite rock surface from oil-wet to water-wet state was also observed. Finally, a tertiary flooding study resulted in 21% increase in oil recovery after secondary water injection, which is assumed to be due to the integrating effect of nano-complex and low salinity brine.