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Article Dans Une Revue Physical Review Fluids Année : 2022

CO2 convective dissolution in a three-dimensional granular porous medium: An experimental study

Résumé

Geological storage of CO2 in deep saline aquifers is a promising measure to mitigate global warming by reducing the concentration of this greenhouse gas in the atmosphere. When CO2 is injected in the geological formation, it dissolves partially in the interstitial brine, thus rendering it denser than the CO2 -devoid brine below, which creates a convective instability. The resulting convection accelerates the rate of the perennial trapping of CO2 by dissolution in the brine. The instability and resulting convection have been intensively discussed with numerical and theoretical approaches at the Darcy scale, but few exper- imental studies have characterized them quantitatively. By using both refractive index matching and planar-laser-induced fluorescence, we measure the onset characteristics of the convective dissolution instability in a three-dimensional porous medium located below a gas compartment. Our results highlight that the dimensional growth rate of the instability remains constant when the CO2 partial pressure in the compartment is varied, in clear discrepancy with the theoretical predictions. Furthermore, within the CO2 partial pressure range studied, the measured growth rate is one to three orders of magnitude larger than the predicted value. The Fourier spectrum of the front is very broad, highlighting the multiscale nature of the flow. Depending on the measurement method and CO2 partial pressure, the mean wavelength is one to three times smaller than the predicted value. Using a theoretical model developed recently by Tilton [J. Fluid Mech. 838, 129 (2018)], we demonstrate that these experimental results are consistent with a forcing of con- vection by porosity fluctuations. Finally, we discuss the possible effects of this forcing by the porous medium’s pore structure on the CO2 flux across the interface, measured in these experiments about one order of magnitude higher than expected. These results obtained in model laboratory experiments show that accounting for sub-Darcy-scale flow heterogeneities may be necessary to correctly predict convective dissolution during CO2 subsurface sequestration.
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Dates et versions

hal-03608494 , version 1 (14-03-2022)

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Christophe Brouzet, Yves Méheust, Patrice Meunier. CO2 convective dissolution in a three-dimensional granular porous medium: An experimental study. Physical Review Fluids, 2022, 7 (3), pp.033802. ⟨10.1103/physrevfluids.7.033802⟩. ⟨hal-03608494⟩
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