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Dissolutional instabilities in fractured and porous rocks

21 mai 2013

Dissolutional instabilities in fractured and porous rocks

Prof. Tony Ladd, University of Florida (Gainesville)

Jeudi 20 juin à 10 h 30

Amphithéâtre Nougaro

Abstract :

Reactive infiltration instabilities occur in a wide range of geophysical and geotechnical systems. The simplest such instability occurs when fluid flows between two soluble plates, which is an idealized model of fractured limestone. Even when the initial aperture is uniform at the nanoscale, an instability in the reaction front develops leading to the formation of pronounced solutional channels or “wormholes”. We have suggested that this instability may explain the onset of large underground caves systems, by allowing a much deeper penetration of reactant than is possible by uniform opening of the fracture.

Predictions of a linear stability analysis in porous rocks vary considerably depending on the underlying model assumptions. In this talk.
I will outline how these different theoretical approaches can be viewed as limiting cases of a more general theory. Our results span the range of geologically feasible Peclet and Damkohler numbers. In particular we show that the convective limit is singular, with a wavelength selection and growth rate that is very sensitive to small amounts of diffusion. We also show that the opposite limit of diffusion-dominated dissolution spans a smaller parameter range than has been supposed.

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