Abstract
Convective mixing of free-phase CO2 and brine in saline aquifers is an established technique to accelerate the CO2 dissolution process. Correct estimation of the convection onset time and rate of CO2 dissolution into brine are two crucial parameters regarding safety issues, as the timescale for dissolution corresponds to the same time over which the free-phase CO2 has a chance to leak out from the storage site. In real practice, underground formations are heterogeneous with a layered structure, but the convective mixing in heterogeneous porous media has received less attention than the homogeneous one. This study aims to develop a basic understanding of the role of layered permeability media (layered structure with variation in permeability vertically) on the behavior of convective mixing via well-controlled laboratory experiments. The effects of layering and layer properties on the rate of dissolution of CO2 in water and geometries of the formed convection fingers are studied using a precise experimental set-up with layered-permeability Hele-Shaw cell geometry. Qualitative (snapshots of convection fingers) and quantitative data (amount of the dissolved CO2 into water) are collected simultaneously for a better understanding of the process. The behavior of convection fingers (after the onset of convection) and the effects of model properties on this mixing process are also discussed.
Highlights
Carbon dioxide (CO2) storage in saline aquifers of huge volume has been recognized as an effective option for decreasing CO2 emission to the atmosphere
This study aims to develop a basic understanding of the role of layered permeability media on the behavior of convective mixing via well-controlled laboratory experiments
The timing of the onset of this instability and the dissolution rate across the phase contact of CO2 and brine solution are the two crucial operational issues when assessing the feasibility of a potential storage site
Summary
Carbon dioxide (CO2) storage in saline aquifers of huge volume has been recognized as an effective option for decreasing CO2 emission to the atmosphere. The associated risk to this leakage is reduced by understanding the trapping mechanisms of CO2 into the brine and by taking suitable measures One of these trapping mechanisms is the dissolution of supercritical CO2 into underground formation water, which is considered as a medium to long-term trapping mechanism. The CO2 dissolution into brine, subsequently causes an increase in density of the brine-CO2 solution, which overlies the less dense brine This situation initiates gravitational instability and eventually leads to density-driven natural convection and increasing the dissolution rate of free phase CO2 into the brine [1,2,3]. The timing of the onset of this instability and the dissolution rate across the phase contact of CO2 and brine solution are the two crucial operational issues when assessing the feasibility of a potential storage site
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