CO₂ dissolution in the presence of background flow of deep saline aquifers

Abstract

We study the effect of background flow on the dissolution and transport of carbon dioxide (CO 2 ) during geological storage in saline aquifers, and include the processes of diffusion, advection, and free convection. We develop a semianalytical model that captures the evolution of the dissolution in the absence of free convection. Using the semianalytical solution, we determine scaling relations for the steady rate of dissolution that follow either J st $ ffiffiffiffiffiffiffiffi Pe R p or J st $ Pe depending on the value of Pe/R, where R represents the ratio of the extent of CO 2 plume to the aquifer thickness and Pe is the Peclet number. Using direct numerical simulations, we provide detailed behavior of the convective mixing during the dissolution. We establish the criteria for forced and mixed (combined free and forced) convection in aquifers that is governed by the background flow. Accordingly, we provide the scaling relations J st $ ffiffiffiffiffiffiffiffi Pe R p and J st $ Ra R representing the forced and free convection asymptotes, respectively, where Ra is a Rayleigh number based on aquifer thickness. The results reveal that the background velocity can delay the onset of free convection and can alter the subsequent mixing. This phenomenon is more profound in the systems subject to strong background flows wherein horizontal component of the velocity field generated by background flow hinders the establishments of vertical component of the velocity field. Finally, by applying the proposed relations to several potential storage sites, we demonstrate the screening process in finding aquifers where the background flow exerts an important influence on the dissolution.

The Role of Water Flow and Dispersive Fluxes in the Dissolution of CO2 in Deep Saline Aquifers

“…The slope in the linear region of the curves increases as the horizontal flow rate decreases, with the no‐flow experiment showing the steepest slope. A decrease in the velocity of the convective fingers due to horizontal water velocity was also found in the numerical study of Emami‐Meybodi, Hassanzadeh, and Ennis‐King (2015). Notably, the slope of the theoretical propagation of the fingers is much higher than the slopes obtained for all flow rates.…”

“…Only a few numerical studies have examined the effect of groundwater flow and hydrodynamic dispersion on the dissolution rate (Emami‐Meybodi, 2017; Emami‐Meybodi, Hassanzadeh, & Ennis‐King, 2015; Hassanzadeh et al, 2009). These studies presented numerical and semianalytical solutions to the coupled flow and transport equations.…”

Instability of a Diffusive Boundary Layer beneath a Capillary Transition Zone

“…Over time, CO 2 gradually diffuses downwards into the resident brine, creating a diffusive boundary layer just beneath a capillary transition zone. This dissolution increases the density of brine, bringing the system to a gravitationally unstable state, which results in natural convection [1]. Such convective mixing increases the rate of dissolution and therefore decreases the likelihood of CO 2 leakage.…”

Semianalytical solutions for contaminant transport under variable velocity field in a coastal aquifer

“…Typical examples of this scenario could be the contaminants leaking through the confining unit from waste disposal and landfill sites, septic tanks, fuel storage tanks and pesticide spills (Woumeni and Vauclin, 2006;Kopp et al, 2010;Bakhtyar et al, 2013;Geng et al, 2016). An analytical solution pertaining to a similar scenario in an inland confined aquifer under uniform velocity field has been developed by Emami-Meybodi et al (2015). In the second scenario, the contaminant source is located upstream of the freshwater flow ( Figure 1b).…”