Pore-scale crude oil displacement: a contribution from nanofluids

Abstract

Immiscible fluid displacement in porous media is one of mechanism in the crude oil production and in enhance oil recovery (EOR), which can be manipulated by chemical additives to engineer the process toward a greater turn-out. Although recent advances in nanofluids have been reported to influence such a process, their interfacial phenomena are likely controversial and need independent cross-examinations. As non-energetically interfacial responsive nanoparticles, silica cores adorned with polyvinylpyrrolidone were examined for their direct contribution to crude oil displacement performance at relatively low concentrations, ranging from 10 to 500 ppm, in the current study. The crude oil displacement was experimented via water-wet borosilicate micromodel and visualized to elucidate pore-scale interfacial phenomena involved. Concentration-dependent property of nanofluids was found, evidenced by different pore-scale mechanisms observed. At low concentrations (10 and 50 ppm), wetting layer flow controlled the oil displacement and led to swelling into pore-space, inducing snap-off event and hence high oil ganglia trapped (>300 ganglia). At higher concentration (100 ppm), nanoparticle self-arrangement at the water wedge was more effective, which induced oscillatory structural disjoining pressure between the oil-aqueous and solid-aqueous interfaces leading to a narrow nanofluid spreading, with snap-off hardly observed. The spatiotemporal displacement performances were decreased. At 500 ppm, structural disjoining pressure developed due to meniscus expansion that pushed oil away from solid phase, and slightly improved oil displacement efficiency with a faster displacing dynamics. The findings amplify nanofluid contribution and emphasize its concentration dependence on immiscible fluid flow in porous media, a potential applicability to various fields including enhanced oil recovery and CO2 geological storage.