Pore–Scale Coupling of Invasion Dynamics and Gas Trapping during Water–Lock Mitigation in Gas–Saturated Porous Media

Abstract

Water-lock effects can impair gas transport in low-permeability hydrate-bearing clayey-silt sediments. However, current screening strategies for candidate mitigation formulations rely primarily on macroscopic measurements and provide limited insight into pore-scale liquid invasion and gas trapping. Previous microfluidic studies have focused mainly on fundamental two-phase displacement behavior, whereas systematic pore-scale frameworks for comparing multiple candidate water-lock mitigation formulations remain limited.In this study, microfluidic visualization and quantitative image analysis were used to compare the invasion behavior of 12 solution systems, including deionized water, simulated seawater, and alcohol-, polymer-, and surfactant-based formulations, in an initially gas-saturated pore network. The A–B transport time (tAB) ranged from 26 to 161 s, whereas the final residual gas saturation (Sgr) ranged from 0.118 to 0.682. A short tAB did not necessarily correspond to low Sgr because several rapidly advancing formulations propagated predominantly along preferential pathways and bypassed substantial portions of the pore space. In contrast, more stable displacement fronts were associated with broader pore-scale sweep and lower residual gas trapping, suggesting that displacement-front stability is closely associated with the final gas distribution and liquid occupancy. Among the tested systems, the C4 formulation, containing 10 wt % polyethylene glycol (PEG), 3.5 wt % NaCl, and 86.5 wt % deionized water, provided the most favorable balance between final liquid-phase occupancy and stabilization time. The 20 wt % ethanol formulation (C3) achieved the lowest Sgr but required a longer stabilization time. These results indicate that formulation screening should jointly consider A–B transport time, displacement-front stability, and final liquid-phase occupancy rather than use propagation rate as the sole criterion. The proposed framework provides a pore-scale basis for the preliminary screening of candidate water-lock mitigation formulations, although further validation in hydrate-bearing clayey-silt sediments is required.