Pore Size and Structural Effects on Salt Precipitation During CO2 Injection in Geo-Sequestration: A Microfluidic Study

CO2 geological sequestration represents a critical strategy to achieving carbon neutrality and mitigating anthropogenic greenhouse gas emissions. However, salt precipitation during CO2 injection induces pore-scale clogging, thereby threatening long-term storage integrity. Existing pore-scale investigations have predominantly idealized homogeneous models, which limit the understanding of salt precipitation dynamics in realistic heterogeneous and fractured systems. In this study, six microfluidic models—covering homogeneous, heterogeneous, and fractured networks—were developed using a self-designed visualization platform integrated with an image-recognition algorithm. This approach enabled direct observation and quantitative characterization of the coupled processes of brine evaporation, salt precipitation, and pore blockage. The results demonstrate that pore geometry and structural heterogeneity exert dominant control over salt precipitation behavior. Smaller pores promote brine retention and accelerate localized evaporation, whereas enhanced heterogeneity facilitates preferential CO2 migration pathways, intensifying residual brine entrapment and promoting heterogeneous salt precipitation. In fractured networks, early drying and precipitation trigger capillary-induced brine backflow from the matrix, resulting in secondary precipitation and a self-enhanced clogging mechanism. These findings elucidate the fundamental pore-scale mechanisms governing salt precipitation dynamics and provide a mechanistic foundation for improving predictive models and optimizing CO2 injection strategies.