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CO2 dissolution in a background hydrological flow

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Unwin, HJT 
Wells, GN 
Woods, AW 


We investigate the long time steady-state dissolution of CO2 in a deep saline aqquifer in the presence of a background hydrological flow. In steady-state, the distribution of CO2 in the groundwater upstream of the aquifer involves a balance between three competing effects: (i) the buoyancy-driven flow of CO2 saturated water; (ii) the diffusion of CO2 from saturated to under-saturated water; and (iii) the advection associated with the oncoming background flow. This leads to three limiting regimes. In the limit of very slow diffusion, a nearly static intrusion of dense fluid may extend a finite distance upstream, balanced by the pressure gradient associated with the oncoming background flow. In the limit of fast diffusion relative to the flow, a gradient zone may become established in which the along aquifer diffusive flux balances the advection associated with the background flow. However, if the buoyancy-driven flow speed exceeds the background hydrological flow speed, then a third, intermediate regime may become established. In this regime, a convective recirculation develops upstream of the anticline involving the vertical diffusion of CO2 from an upstream propagating flow of dense CO2 saturated water into the downstream propagating flow of CO2 unsaturated water. For each limiting case, we find analytical solutions for the distribution of CO2 upstream of the anticline, and test our analysis with full numerical simulations. A key result is that, although there may be very different controls on the distribution and extent of CO2 bearing water upstream of the anticline, in each case the dissolution rate is given by the product of the background volume flux and the difference in concentration between the CO2 saturated water and the original aquifer water upstream.



gravity currents, porous media

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Journal of Fluid Mechanics

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Cambridge University Press (CUP)
HJTU was funded by an EPSRC Doctoral Training Partnership scheme (grant EP/J500380/1). Data relating to this publication is available in Unwin & Wells (2015).