Dynamic CO2 trapping mechanisms driven by pore-scale capillary heterogeneity

초록

Capillary heterogeneity, resulting from spatial variations in pore size and wettability that control capillary entry pressure, influences how carbon dioxide (CO2) migrates and becomes trapped in geologic formations. Although its influence is widely acknowledged, direct experimental evidence at the pore scale has remained limited. To address this gap, we apply an integrated approach that combines mineralogical and pore-structure characterization, two-phase flow experiments, synchrotron-based mu CT, and numerical simulations to capture how CO2 migrates through a heterogeneous sandstone. Our results show that microporous zones formed by intergranular minerals act as capillary barriers that locally restrict CO2 migration, leading to selective bypassing behavior and underutilization of pore space. These flow restrictions create spatial contrasts in capillary entry pressure, which govern time-dependent ganglion redistribution. Even under steady injection, CO2 ganglia undergo fragmentation, reconnection, and reconfiguration driven by capillary and viscous forces. Importantly, this dynamic behavior persists beyond breakthrough, as CO2 rearrangements continue even after initial displacement, progressively accessing previously unswept regions. While some regions remain permanently inaccessible due to persistent capillary barriers, others become increasingly invaded as local thresholds are overcome. These findings indicate that CO2 trapping is not instantaneous but evolves dynamically in response to heterogeneous pore structures. Incorporating such time-dependent processes into reservoir-scale models is essential for improving predictions of CO2 plume migration, sweep efficiency, and long-term storage performance. The pore-scale mechanisms observed here also provide insight into broader multiphase flow systems, including hydrogen storage and enhanced oil recovery, where fluid redistribution under capillary control plays a critical role in system behavior.

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