Synergistic effect of silica nanofluid and biosurfactant on bitumen recovery from unconventional oil

In this paper, the nanofluid (bionanofluid) was prepared by dispersing SiO2 nanoparticles (NPs) in water (biosurfactant-sophorolipid) solution. The nanofluid (bionanofluid) stability was measured through zeta potential measurement, DLS (dynamic light scattering) measurement and steady-state fluorescence measurement. The critical salt concentration (CSC) for bionanofluids was 3%. The results indicated that sophorolipid could improve the nanofluids stability in liquid, and the steady-state fluorescence measurement and zeta potential illustrated the sophorolipid adhered on the surface of the SiO2 nanoparticles, and then the steric hindrance between different nanoparticles increased significantly. It was also found that the silica nanoparticles and biosurfactant had obvious synergistic effect on bitumen recovery from unconventional oils. The nanofluids and bionanofluids viscosities increased with high nanoparticles concentration and high salinities. The bionanofluid alter the solid wettability from oil-wet to inter medium-wet, the contact angle (oil-minerals) increased from 58.5° (in deionized water) to 87.6° (bionanofluid solution). The bionanofluid could reduce the oil-water interfacial tension, and the interfacial tension was lower than the surfactant solution used only. The toluene/deionized water interfacial tension was 36.1 mN/m, when deionized water was replaced by the sophorolipid solution, the interfacial tension was 8.4 mN/m, but the interfacial tension of toluene/bionanofluid solution was decreased to 7.1 mN/m. The similar downward path of interfacial tension occurred when the oil phases were cyclohexane, n-heptane and bitumen. The oil/water interfacial tension decreased with higher surfactant concentration and nanoparticles concentration. In the end, the structural disjoining pressure was calculated to explain the synergistic effect. The structural adjoining pressure is proportional to the nanofluid velocity of enhancing oil (VC). VC increased with the decrease diameter of nanofluids, but VC decreased with the decrease of effective nanofluids concentrations. The bionanofluids could decrease the nanofluids diameter and increase the nanofluids effective concentrations, leading to the increasing of VC ,structural adjoining pressure and the oil recovery.