When Size Matters: How CO₂ Nanobubbles Outperform Microbubbles in Two-Phase Flow

We study the effect of gas bubble size on immiscible two-phase flow in porous media by directly comparing CO₂ nanobubbles (~100–200 nm) and microbubbles (~10–100 µm). Both are introduced into surfactant solutions and injected into model porous systems under controlled flow conditions. Nanobubbles significantly reduce interfacial tension and contact angle, leading to a shift in capillary number and wettability. Flow visualization and pressure-drop measurements reveal that nanobubbles produce more uniform displacement fronts and reduce early breakthrough, while microbubbles generate unstable fingering and preferential flow paths. We hypothesize that the enhanced performance of nanobubbles arises from their ability to enter smaller pore throats and locally alter interfacial stresses. This scale-dependent interaction is expected to influence capillary trapping, phase connectivity, and the stability of the displacement front. By controlling bubble size and interfacial properties, it may be possible to tune two-phase flow behavior in porous media for improved fluid redistribution and reduced channeling.