Multiphase flow displacement application of novel green nanoparticle synthesis in glycerol and reconfigurable nanoemulsions in reservoir-on-a-chip

Nanofluids and oil in water (O/W) nano/micro emulsions have been extensively investigated for their potential in multiphase displacement applications such as enhanced oil recovery (EOR). However, the potential of metal nanofluids and water-in-oil nanoemulsions (W/O) has not been readily studied and the under-lying mechanisms are yet to be investigated. Moreover, most nanofluids pose toxicity risks to reservoirs, and a high polydispersity index of conventionally syn-thesized nanofluids adversely impacts displacement efficiencies. Hence, in this study, we synthesized two injection fluids including, a novel green nanofluid comprising of ultra-small silver nanoparticles (NPs) in glycerol and reconfigurable nanoemulsions to investigate their impact on displacement efficiencies. We have carried out the synthesis of green nanofluid comprising silver NPs in a customized microfluidic (Mf) chip, with 18 omega-shaped micromixers, by using glycerol as a promising green solvent and reducing agent at various concentrations (10-80 %), and simultaneous comparison of the results from batch synthesis. Interestingly, the experimental findings depicted that by varying different parameters, the spherical silver nanoparticles with an average ultra-small particle diameter of < 2nm were obtained at all glycerol concentrations (10-80 %) and variables, as compared to batch synthesis (giving a yield of 10-fold larger particles). The synthesis was then confirmed by Dynamic Light scattering (DLS), UV-visible spectroscopy, and Tunnelling Electron Microscope (TEM). Subsequently, the dis-placement efficiencies were then investigated in a reservoir-on-a-chip platform (filled with fluorescence-doped oil) for real-time visualization, quantification and pore-scale investigation. The measurement data for green nanofluid revealed the wettability alteration and IFT reduction with the increase in viscosity and size of NPs. No significant effect of the IFT on sweep efficiencies was observed, however, the contact angle of the injection fluids shifted from an oil-wet state (101◦-113◦) towards an intermediate wettability state (90◦-97◦) over 2 minutes. A shift to-wards intermediate wettability in a short time indicated the influence of AgNPs in displacing oil ganglia by structural disjoining pressure. It was reported that a critical glycerol viscosity (30 %) was essential to increase the sweep efficiency by 5 % in microfluidics-synthesized nanofluid (1.7 nm) and by 8 % in benchtop synthesized nanofluid (3.3 nm). Finally, the NPs-surfactant assemblies between SiO2 and Poly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane] copolymer were in-vestigated for the synthesis of reconfigurable nanoemulsions. The buckling phenomena was confirmed between pH 5 and 6 and nanoemulsions were synthesized with 3 different Oil: NPs concentrations i.e., 80:20, 70:30 and 60:40 at pH 3, 5, 6, and 8 (pH 3 and 8 taken as control groups). The sweep efficiency gradually increased in the order of 60:40 < 70:30 < 80:20, with the highest sweep efficiency obtained in the case of 80:20 nanoemulsions at pH 5, pH 6 and pH 5 in case of 70:30 nanoemulsions respectively, due to the displacement of oil because of formation of wedge film and in-situ emulsification.