EPJ E Colloquium - Convective mixing in porous media: A review of Darcy, pore-scale and Hele-Shaw studies

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Published on 19 December 2023

When a porous medium is filled with two fluid layers of different density, with the heavier fluid sitting on top of the lighter one, the system may become unstable. Due to the vertical density contrast, convective finger-like structures can form and accelerate fluid mixing. This configuration is representative of a variety of systems of practical interest, particularly in geophysical processes.

The regular polygonally patterned ridges observed in dry salty lakes are the surface signature of the convective transport of salt in the subsurface porous soil, a fundamental process in arid regions. Formation of sea ice or solidification of multicomponent alloys may originate mushy layers, which consist of porous media filled by a multicomponent fluid subject to density gradients. It follows that the consequent convective motions control the solidification dynamics. The long-term storage of carbon dioxide in underground geological formations is also driven by convection. These examples are representative of why understanding convective mixing in porous media is crucial, for instance, to tackle grand societal challenges like energy transition, or to predict how environmental systems respond to climate change.

The fluid mechanics underlying porous media convection is made complex by the multiscale and multiphase character of the flow. As a result, a combination of different complementary approaches has been deployed to elucidate the intricate physics of convection in porous media. In a new Colloquium published in EPJE, Marco De Paoli (University of Twente, The Netherlands and TU Wien, Austria) reviews recent numerical, experimental, and theoretical findings, discusses their limits of applicability, and highlights possible future research directions.