Chaotic Mixing and Biochemical Reactions in Porous Media

Orateur : Tanguy LE BORGNE (Observatoire des Sciences de l’Univers de Rennes, Université de Rennes 1)

Mixing and reaction of chemical elements and bacteria transported in flow through soils and rocks, and through industrial and biological porous media, play a fundamental role in a range of applications in the field of water resources (water quality, soil remediation, artificial recharge, filtration), energy (geothermal energy, enhanced oil and gas recovery, CO2 sequestration), and the study of biogeochemical cycles in hydrological systems (carbon and nitrogen fluxes in watersheds, microbial processes in soils and river beds). We have recently demonstrated, from high resolution simulations and Laser Induced Fluorescence experiments (Figure), that the topology of porous structures leads to the emergence of chaotic dynamics in laminar flows, calling into question current models of transport in porous media. I will first present the currently debated hypotheses to explain these phenomena and propose a theoretical framework relating the intensity of chaotic mixing to the porous media structures. I will then discuss the consequences of chaotic mixing for solute transport, chemical reactions and microbial processes using the lamellar theory of mixing. In this framework, we quantify the effect of chaotic stretching on concentration statistics, reaction kinetics and concentration gradient distributions, which control the response of bacteria to the transport and mixing of nutrients and biochemical signals in porous media.

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