Wettability Regulated Two-Phase Flow of Supercritical CO₂ and Water in Confined Nanochannels

Supercritical carbon dioxide (scCO₂) has emerged as a promising agent in enhanced oil recovery (EOR) due to its ability to reduce interfacial tension and enhance oil mobility in reservoirs. Water is ubiquitous in oil reservoirs, yet the underlying mechanisms governing scCO₂ transport in the presence of water within nanoscale channels remain inadequately understood. Using molecular dynamics simulations combined with analytical models, this study explores the two-phase flow behavior of scCO₂ and water in confined nanochannels, emphasizing the effects of water saturation (S_w) and channel wettability. It is found that in hydrophilic nanochannels, water preferentially adsorbs onto channel walls, forming thin films that coalesce into a water bridge at higher S_w. This water bridge drastically impedes scCO₂ transport, reducing the flow capacity by up to 95%. Conversely, hydrophobic nanochannels exhibit water clustering in the channel center, which facilitates a higher scCO₂ mobility. At elevated S_w, the flow pattern transitions from Poiseuille to Couette flow, further mitigating the decline in the scCO₂ transport capacity. Analytical models accurately predict these behaviors, highlighting the interplay among channel wettability, S_w, and nanoscale confinement in dictating scCO₂ transports. This research deepens our understanding of scCO₂-water interactions and offers a theoretical foundation for optimizing scCO₂-EOR processes under realistic reservoir conditions.