Secondary oil recovery using graphene-based amphiphilic Janus nanosheet fluid at an ultralow concentration

Nanofluid of graphene-based amphiphilic Janus nanosheets produced high-efficiency tertiary oil recovery at a very low concentration (0.01 wt %). The more attractive way is to use nanofluid during the secondary oil recovery stage, which can eliminate the tertiary stage and save huge amounts of water, especially at times when the price of oil is low. Here, we continue to report our findings on the application of the same nanosheets in secondary oil recovery, which increased oil recovery efficiency by ≤7.5% at an ultralow concentration (0.005 wt %). Compared with nanofluids of homogeneous nanoparticles, our nanofluid achieved a higher efficiency at a much lower concentration. The nanosize dimension of this two-dimensional carbon material improves transport in rock pores. After single-side surface hydrophobization of oxidized graphene with alkylamine, the partial restoration of the graphitic sp² network was detected by Raman, ultraviolet.visible, etc. The amphiphilic Janus nature of nanosheets led to their unique behavior at toluene.brine interface. Oil immersion testing clearly showed the change in the shape of the droplet. The three-phase contact angle decreased from 150° to 79°, indicating the change in the wettability of the solid surface from oleophilic to oleophobic. On the basis of the measured three-phase contact angles, the interfacial tension in the presence of the nanosheets was further calculated and was lower than the interfacial tension without the nanosheets. These interfacial phenomena can help residual oil detach from the solid surface, which contributes to the improved oil recovery performance.