Pore-scale modeling of complex reacting flow by cross-linked polymers in porous media

Cross-linked polymer gels are widely employed as deep profile control agents to enhance oil recovery, effectively mitigating channeling and improving sweep efficiency in heterogeneous reservoirs. However, the underlying mechanisms coupling cross-linking reactions, transport processes, and subsequent water flooding—particularly at the pore scale—remain inadequately understood. In this study, a novel micro-continuum reactive–transport solver was developed within the OpenFOAM-based Darcy–Brinkman–Stokes framework, incorporating a non-Newtonian constitutive model and kinetic source terms for cross-linking reactions. This solver was used to simulate the reaction–transport behavior of cross-linked polymers in porous media. Following validation, we systematically investigated polymer behavior across different stages and under varying reaction–transport regimes. The results reveal that during the injection stage, the spatial distribution of reaction products is predominantly controlled by the first Damköhler number (DaI). With increasing DaI, the morphology of polymer deposits evolves from dispersed low-concentration zones to highly concentrated accumulations near the inlet, resulting in the significant flow blockage. Throughout the gelation stage, the interplay between the DaI and the second Damköhler number (DaII) leads to four distinct spatial distribution patterns, each corresponding to a specific dominant mechanism. These patterns critically influence gel placement, concentration gradients, and sweep efficiency during the subsequent flooding. In the water flooding stage, the evolution of the residual resistance factor is highly dependent on the initial gel structure. Different spatial patterns exhibit markedly distinct flow resistance behaviors, with gels formed under high-reaction and low-diffusion conditions demonstrating superior stability against water flush. This work establishes a quantitative pore-scale framework for unraveling the coupled dynamics of reaction, transport, and scouring in cross-linked polymer systems.