Quantifying Regime Transition of Mineral Precipitation in a Microfluidic Fracture

Abstract Mineral precipitation is ubiquitous in subsurface environments, influencing processes such as karst evolution and carbon mineralization. While precipitation dynamics have been extensively studied in porous media, the pattern formation and transitions in fractured media remain underexplored. In this study, we develop a novel experimental system to investigate precipitation dynamics in microfluidic fractures by integrating charge‐coupled device camera, micro‐PIV, and confocal microscopy. Flow‐through experiments on CaCO 3 precipitation are performed by co‐injecting Na 2 CO 3 and CaCl 2 under controlled flow rates Pe and saturation indices SI. Real‐time imaging of precipitation dynamics and velocity fields revealed two distinct patterns. At low Pe and low SI, mineral precipitation exhibits precipitation band acting as a barrier that inhibits mixing of the reactants and results in minimal permeability reduction. In contrast, at high Pe and high SI, the system transitions to precipitation clusters, characterized by widespread particle distribution that significantly reduces permeability. We demonstrate that this pattern shift is governed by the balance between fluid shear forces and repulsive forces between CaCO 3 particles. When repulsive forces dominate, particles cannot aggregate, leading to band formation, whereas shear‐induced aggregation promotes cluster growth. Theoretical analysis is developed to interpret the regime transition, and a phase diagram mapping precipitation regime as a function of Pe and SI shows well agreement with experimental results. These findings provide critical insights into fracture mineral precipitation, which are crucial for predicting injectivity and permeability in CO 2 mineralization processes.