Oil recovery enhancement by Nanobubbles: Insights from High-Pressure micromodel studies

Aqueous nanobubble solutions (NBs) have demonstrated a remarkable ability to displace hydrophobic fluids (e.g. oil) from porous media compared to blank water, although the underlying mechanisms remain unclear. Through detailed characterization of fluid behavior within porous spaces under controlled conditions, microfluidics can help uncover the fundamental origins of the NB-induced effects.

We systematically evaluate the impact of NBs on two-phase flow dynamics within porous media by applying glass micromodels that mimic both extreme wettability conditions: strongly hydrophilic (water-wet "WW") and strongly hydrophobic (oil-wet "OW"). An innovative system that combines membrane dispersion technique with microfluidic flow was used to generate NBs at elevated pressures for flooding tests.

In OW scenarios, NBs demonstrated superior sweep efficiency compared to distilled water, achieving more uniform front propagation and reducing bypassed oil volumes. The improvement can be attributed to the interfacial activity of NBs along with their specific interactions with solid surfaces. In particular, NBs lowered the interfacial tension (IFT) between the oil and aqueous phases, leading to weaker capillary forces that aid in effective oil mobilization. At the pore walls, NBs induced a slippage effect that reduced the pressure drop across OW media, further facilitating displacement. Aside from these fundamental insights, our results demonstrate the utility of N₂ NBs for oil recovery and related applications at elevated pressures, which are often encountered in practical settings.