Anomalous transport in vesicular porous media

Transport of chemical species in complex structured vesicular porous media with mesoscale fluid-filled vugs and cavities exhibit anomalous features that cannot be captured by Fickian transport approaches. The anomalous behavior originates from the occurrence of non-Gaussian and multiscale velocity distributions caused by porous medium structural complexities. Local flow instabilities, vorticities, stagnant zones, and reverse flow result in a significantly different velocity distribution for the tracer compared to the fluid. We investigate the nonreactive transport of particles in a porous medium with an embedded cavity located at the center. The Darcy-Stokes flow is solved for the matrix and cavity system, then the transport is modeled via particle tracking method. The effect of the size and shape of the cavity and the flow field features on tracer transport is quantified. Breakthrough curves confirm anomalous transport at the cell problem. We derive the upscaled continuous time random walk (CTRW) framework for the vesicular medium with a high degree of disorder. The key controlling factors that substantially affect the spread of tracer across all scales of heterogeneity are addressed.