Wettability-controlled fracture-to-matrix transition in salt precipitation in hydrophilic fractured rocks

• Small wettability shift drives fracture-to-matrix salt transition • Stable corner film promotes aggregated crystal growth and fracture clogging • Receding films at higher contact angle shift salt growth into the matrix Evaporation-induced salt precipitation during gas injection can significantly reduce reservoir permeability and injectivity in subsurface energy systems and geological CO 2 storage. Although wetting and capillary processes play a central role in these phenomena, the impact of wettability variations within the hydrophilic regime on salt precipitation in fractured porous media remains poorly understood. Here, we investigate how subtle changes in surface wettability regulate capillary transport, evaporation dynamics, and salt crystallization behavior through the impact on corner-film persistence. Using dual-porosity microfluidic chips comprising fracture channels and microporous matrix networks, we investigate the brine drying and salt precipitation dynamics across contact angles (θ) ranging from 8° to 31°. The chips were saturated with saline water and then subjected to gas injection, followed by evaporation-induced salt precipitation. Time-lapse microscopy was used to track brine redistribution and salt crystallization during drying, with quantitative analysis of the final salt morphology and spatial distribution. Three distinct precipitation regimes are identified: (1) a fracture-dominated regime (θ < 10°), characterized by stable corner films and continuous aggregated salt crystal growth in fractures; (2) a matrix-dominated regime (θ > 25°), where corner film recession limits connectivity and promotes bulk crystal formation in the porous matrix; and (3) a transitional regime (10° < θ < 25°) exhibiting mixed behaviors. Our results demonstrate that even minor wettability variations within hydrophilic regimes can dramatically alter salt precipitation dynamics and the fracture sealing behavior, with distinct implications subsurface energy projects and systems.