Anomalous Transport in a Porous Medium with Randomly Packed Ellipse Cavities

We investigate the transport of nonreactive tracers in a binary porous medium with randomly packed ellipse fluid-filled cavities. Anomalous transport features, such as early arrival time and long tailing, are observed due to the high contrast in medium properties and highly complex structure of fluid velocity. We use a particle tracking method to quantify the transport features of the domain. Then, a continuous time random walk (CTRW) framework builds on the tracer transitions in time and space to represent an upscaled model. We study the effect of several key parameters on the anomalous transport process. The parameters include: cavity aspect ratio, porous background permeability, and Peclet (Pe) number. With the increase in Pe, a longer tailing and a larger residence time are observed, which presents a stronger anomalous feature. A similar situation corresponds to decreased porous medium permeability, which results in wider breakthrough curves. A longer tailing arises in the case of elongated cavity.The purely advective transport in the medium is investigated at Pe=$\infty$. This is considered a limit case for the anomalous behavior of the system. One can refer to this case as the most extended tail possible for each cavity arrangement. The widest breakthrough curves for a Pe=infty correspond to larger aspect ratios of the cavity and a lower permeable matrix.We show that the upscaled CTRW model can closely predict breakthrough curves in a binary medium with randomly distributed ellipse cavities.These findings give new insights into transport in vesicular and vuggy porous media.