Experimental study of miscible Rayleigh-Taylor convection in a granular porous medium
Résumé
More than 60% of greenhouse gas emissions are due to CO2 released from fossil fuels and
industrial processes [1]. It is expected that by 2035, the expected increase in CO2 emissions will be
37.2 Gt/yr [2]. To reduce the resulting further adverse effects in climate changes, geological
sequestration of CO2 provides an effective solution for carbon capture and storage (CCS) [2-4].
Dissolution trapping of CO2 in deep saline aquifers is a trapping mechanism that allows for long
term storage. When CO2 is injected into the subsurface geological layers, the supercritical CO2
(sCO2) dissolves into the aquifer’s aqueous solution positioned below. The formation of a layer of
CO2-enriched brine at the upper interface of the liquid domain results in unstable stratification
which evolves into gravitational convection [2-5].
To evaluate the storage capacity and the efficiency of the trapping, it is necessary to understand
the dynamics of the instabilities and convection, and the affect of granular media properties on
them. To do so, we perform a 2D experimental study in a 3D granular medium and use Darcy
scale simulations to complement our experimental findings [6]. Analog experiments are
performed by using two miscible fluids with a density contrast between them. In doing so we
decouple the gravitational instability process from the dissolution process; the latter is not
modeled in our experiment. We match the refractive index of the fluids to that of the granular
medium to allow for optical measurement of the concentration field. We observe that there is
substantial difference in convection development time scales between the experimental results
and the Darcy scale simulations performed with the experimental macroscopic parameters
(porosity, permeability, dispersivity lengths, density contrast). We attribute this to the role played
by pore scale heterogeneity of the velocity field, which cannot be predicted by Darcy scale models.
This would suggest that Darcy scale simulations [2, 4,6] significantly overestimate the typical time
scale of the convection.
[1] Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change, IPCC 2014.
[2] Emami-Meybodi, H., Hassanzadeh, H., Green, C. P., & Ennis-King, J. (2015). Convective dissolution of CO2 in saline aquifers: Progress in modeling and experiments. International Journal
of Greenhouse Gas Control, 40, 238-266.
[3] Bachu, S. (2008). CO2 storage in geological media: Role, means, status and barriers to
deployment. Progress in energy and combustion science, 34(2), 254-273.
[4] Pau, G. S., Bell, J. B., Pruess, K., Almgren, A. S., Lijewski, M. J., & Zhang, K. (2010). High-resolution
simulation and characterization of density-driven flow in CO2 storage in saline aquifers. Advances
in Water Resources, 33(4), 443-455.
[5] Nadal, F., Meunier, P., Pouligny, B., & Laurichesse, E. (2013). Stationary plume inducedby carbon
dioxide dissolution. Journal of Fluid Mechanics, 719, 203-229.
[6] Dhar, J., Meunier, P., Nadal, F. & Méheust, Y. (2021). Convection dissolution of CO2 in 2D and
3D porous media: the impact of hydrodynamic dispersion. Submitted to Physics of Fluids.
