Pore-Scale Gas Invasion and Residual Liquid Trapping in a Hydrophilic Microfluidic Network

Abstract Gas invasion into liquid-saturated hydrophilic porous media is governed by interfacial, wetting, viscous, and pore-scale effects that control pathway selection and residual liquid trapping. However, how liquid composition influences gas-pathway establishment, postbreakthrough redistribution, and final liquid retention remains insufficiently understood. Here, nitrogen displacement was visualized in a hydrophilic glass microfluidic network initially saturated with 12 liquid systems, including water, 3.5 wt % NaCl brine, and formulations containing ethanol, polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), or sodium dodecylbenzenesulfonate (SDBS). Breakthrough time, liquid-saturation evolution, final residual liquid saturation, stabilization time, and final gas morphology were quantified. Three invasion modes were identified: preferential-channel flow, dendritic expansion, and network-like expansion. Breakthrough times ranged from 1 to 67 s, showing that rapid formation of a spanning gas pathway did not necessarily correspond to extensive liquid removal. PEG system W5 showed the highest final residual liquid saturation (∼0.42), whereas SDBS system W11 showed the lowest (∼0.07), corresponding to a final gas occupancy of ∼0.93. SDS system W8 and SDBS system W10 both exhibited high final gas occupancy together with relatively short stabilization times. Lower measured air–liquid surface tension was associated with broader branched invasion in some systems, while final liquid removal likely reflected coupled effects of viscosity, wettability, and pore-structure heterogeneity. Film-like residual liquid and locally isolated gas regions further showed that extensive gas occupation did not necessarily ensure complete connectivity among the optically resolved gas-filled regions. These results reveal a decoupling between breakthrough dynamics and final liquid removal and provide mechanistic pore-scale insight relevant to evaluating water-block mitigation in hydrate-bearing sediments.