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 (Sw) 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 Sw. 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 Sw, 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, Sw, 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.