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Digitation visqueuse dans les milieux poreux [Viscous fingering in porous media]

Lorsqu'un fluide déplace un autre fluide plus visqueux dans un milieu poreux, l'interface ne reste pas plane mais se déforme sour forme de ''doigts''. Nous étudions expérimentalement et théoriquement l'influence de cette digitation visqueuse sur l'étalement d'échantillons en relation avec des applications en chromatographie chimique, en pollution des sols et en séquestration de dioxyde de carbone liquéfié. [ When a fluid displaces a more viscous one, the interface between the two fluids does not remain flat and perpendicular to the flow axis. Instead, since, for a given pressure gradient, the less viscous fluid moves faster than the more viscous one, it deforms the interface into fingers growing in time. Such a fingering instability occurs typically when less viscous water displaces more viscous oil in underground reservoirs leading to viscous fingering which produces flow nonuniformity and reduces oil recovery. Fingering poses also problems in contaminant transport in aquifers, in packed bed reactors, and is particularly detrimental to chromatographic separation techniques. Indeed, since samples injected in chromatographic columns or pollution zones have generally a viscosity different from that of the carrier fluid, fingering occurs at the front or tail of the sample zone when the sample viscosity is, respectively smaller or larger than that of the invading fluid. In any case, this instability leads to distortion and broadening of the samples. The resulting deterioration of the separation can be serious, especially for highly concentrated samples in preparative, with polymeric samples in size-exclusion chromatography and highly viscous aquifer contaminants. In this context, it is our goal to investigate both experimentally and theoretically the influence of viscous fingering on the spreading of viscous samples. ]



équipe


Fabian BRAU


disciplines et mots clés déclarés


Chimie théorique

chromatographie digitation pollution