Residual NAPL Architectures in Fractures: Insights From Microfluidic Experiments

Abstract Understanding residual non‐aqueous phase liquid (NAPL) architectures in fractures is crucial for predicting NAPL dissolution and depletion in fractured aquifers. Although NAPL infiltration and dissolution in porous media have been widely studied, residual NAPL architectures and associated mechanisms in fractures remain poorly understood. To address this, we conducted 162 water‐NAPL displacement experiments using microfluidics. Three distinct residual NAPL architectures were identified, Pools Pattern (PP), Ganglia Pattern (GP), and Mixed Pattern (MP), affected by aperture heterogeneities and flow rates. Experiments combined with numerical simulations revealed that aperture anisotropy, roughness and flow rate determine balance between local capillary and viscous forces, driving NAPL entrapment mechanisms that form observed architectures. Capillary‐trapping leads to NAPL pools (PP), viscous‐trapping leads to ganglia (GP), and a combination of both mechanisms leads to MP. This work elucidates the mechanism of residual NAPL architectures in fractures and lays a foundation for modeling residual NAPL dissolution in fractured aquifers.