CO ₂ Exsolution and Residual Trapping Influenced by Heterogeneity During Imbibition in Conglomerates: A Core‐Scale Multiphase Flow

Abstract Although conglomerates composed of clasts and matrix are commonly interbedded with sandstones at geologic CO 2 storage sites, their residual trapping behavior remains poorly understood. This study investigates the influence of clast‐induced heterogeneity on residual CO 2 trapping during water imbibition, using two natural conglomerate cores from the Janggi Basin, Republic of Korea. Petrophysical characterization revealed wide permeability variations and distinct spatial variations of clasts across the two cores, which were incorporated into core‐scale multiphase flow simulations. Results show that clasts not only act as flow barriers but also govern the internal pressure field, leading to localized CO 2 exsolution and heterogeneous trapping behaviors. Pressure gradients across clasts triggered phase transitions from dissolved to supercritical phase CO 2 , which accumulated and became immobilized within narrow matrix pathways and clast interiors that are typically inaccessible to supercritical phase CO 2 . Additionally, clast‐induced preferential water flow stabilized residually trapped CO 2 by limiting dissolution and mobilization, thereby expanding the spatial domain of residual trapping and enhancing its efficiency. Despite pronounced heterogeneity, the residual trapping efficiencies observed (34%–78%) were comparable to those reported for homogeneous sandstone and carbonate formations. These findings highlight the potential of well‐characterized conglomerates as viable targets for geological CO 2 storage.