Speaker
Description
Geological carbon dioxide (CO$_2$) sequestration in deep saline aquifers is a promising strategy for mitigating the impacts of anthropogenic CO$_2$ emissions on global climate change \cite{Huppert2014,Sahu_Neufeld_2023}. The effectiveness of CO$_2$ sequestration relies on efficient mixing of CO$_2$ with resident brine, which can be investigated through the study of gravity-driven flow or Rayleigh–Taylor instability in stratified porous media. While numerous studies \cite{Rapaka2008, MUSUUZA2009796, MUSUUZA2011417, PhysRevLett.106.104501, EMAMIMEYBODI2015238, Hewitt_2022} have examined density-driven flows in single-layer porous media to predict the onset of convective instability and the subsequent evolution of mass transport, natural aquifers and many engineered systems are inherently stratified, comprising layers with distinct permeabilities and porosities. Such heterogeneity can fundamentally modify both the onset of convective instability and the ensuing flow patterns, yet its influence remains poorly understood.
In this study, we investigate gravity-driven flow of a dense fluid in a two-layered porous medium using a combination of experimental and theoretical approaches. The system consists of two porous layers with different permeabilities, initially saturated with a lighter fluid in the lower layer and a denser fluid in the upper layer. Our objective is to determine the critical density difference required for the onset of fingering instability of the denser fluid penetrating into the lighter fluid under gravity, accounting for the restrictions imposed by permeability contrast between the layers and fluid viscosity. A mathematical model based on Darcy’s law and solute transport equations is formulated and analyzed using linear stability analysis to obtain the critical Rayleigh number for the onset of convective instability. The theoretical predictions are validated through laboratory experiments conducted in glass bead–packed columns.
The post-onset flow dynamics are further analyzed in terms of the growth rate and frequency of fingers, as functions of the density difference between the upper and lower fluids and the permeability ratio of the two layers. The results provide insight into the role of permeability contrast and fluid density differences in governing solute transport and mixing dynamics in stratified porous media, with direct relevance to geological CO$_2$ sequestration.
| Country | India |
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