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Abstract This study investigates the impact of initial injection conditions on colloid transport and retention in porous media. Employing both uniform and flux‐weighted distributions for the initial colloid locations, the research explores diverse flow scenarios, ranging from simple Poiseuille flow to more complex geometries. The results underscore the pivotal role the injection mode plays on the shape of colloid retention profiles (RPs), particularly those that display anomalous non‐exponential decay with distance. Broadly, uniform injection yields multi‐exponential profiles, while flux‐weighted injection can lead to nonmonotonic profiles in certain conditions. The study identifies preferential flow paths as a key factor in producing nonmonotonic RPs. Notably, variations in fluid velocity, colloid size, and ionic strength affect attachment rates near the inlet but do not significantly alter the qualitative transition between multi‐exponential and nonmonotonic profiles. The study emphasizes that the chosen injection mode dictates retention profile shapes, highlighting its crucial role in porous media colloid transport. These insights provide a possible partial explanation of previously observed anomalous transport behaviors, urging consideration of injection conditions in interpretations of experiments, where they can be difficult to accurately control and measure with high precision. 

This study introduces a novel theoretical model for upscaling colloid transport from the grain scale to the Darcy scale under both favorable and unfavorable conditions. The model integrates colloid interception history, where an interception occurs when colloids enter the near-surface zone within 200 nm of a collector, to capture the traditional exponential retention profile, as well as the anomalous, non-exponential behaviors observed under unfavorable conditions. The development of this theoretical model is based on a two-stage framework: first, upscaling from the grain scale to the single-interception scale, followed by upscaling from the single-interception scale to the Darcy scale. The initial stage addresses the distribution of colloids corresponding to a given interception order. The second stage focuses on the distribution of colloids across multiple interception orders. The key innovation of this work is the inclusion of the colloid removal process, where a fraction, denoted by $$\alpha$$, is removed at each encountered interception, rather than with each grain passed, as specified by classical colloid filtration theory. Our model accounts for scenarios under unfavorable conditions wherein if $$\alpha$$ remains constant, the distribution is exponential, albeit shallower relative to favorable conditions. Additionally, the model considers cases where $$\alpha$$ varies with interceptions, leading to multi-exponential and nonmonotonic retention profile shapes. In both scenarios, the proposed theoretical model offers a mathematical representation of colloid retention profiles under favorable and unfavorable conditions, including those exhibiting anomalous shapes.