Pore-throat structure evolution governs multiphase flow in sustainable subsurface carbon and energy engineering

Pore-throat structure evolution plays a critical role in controlling immiscible multiphase flow in subsurface systems relevant to carbon sequestration, hydrogen storage, hydraulic fracturing, acidizing, and microbially induced mineralization. However, how such structural changes reshape flow regimes and displacement efficiency remains insufficiently understood. This work integrates multiscale experiments and pore-scale simulations to elucidate the governing mechanisms. Two-dimensional nuclear magnetic resonance measurements on shale samples exposed to slickwater demonstrate that different pore-size classes respond unevenly to chemical perturbation: clay-scale pores contract slightly, mesopores expand, and macropores remain largely unchanged. These alterations collectively modify pore occupancy and transport properties. To isolate the intrinsic effect of pore-throat geometry, pore-scale numerical simulations were performed by uniformly scaling grain sizes using a geometric factor α. Smaller pore throats (α = 1.0) produce highly unstable capillary fingering dominated by recurring snap-off and coalescence, generating extensive cluster populations. Moderate enlargement (α = 0.9) reduces these interfacial instabilities, while further enlargement (α = 0.8) yields more compact invasion with no snap-off events. The combined experimental and numerical results demonstrate that pore-throat evolution governs multiphase flow by modulating capillary thresholds, interface stability, and cluster dynamics. This framework enhances mechanistic understanding of displacement behavior in evolving porous media and informs the sustainable design of subsurface carbon and energy engineering processes.