Geological Carbon Sequestration mitigates climate change by capturing
and storing carbon emissions in deep geologic formations. Dissolution
trapping is one mechanism by which CO2 can be trapped in a deep
formation. However, heterogeneity can significantly influenced
dissolution efficiency. This work addresses the injection of CO2 in
perfectly stratified saline formations under uncertainty. Monte Carlo
two-phase flow compositional simulations involving the dissolution of
CO2 into brine and evaporation of water into the CO2-rich phase are
presented. We systematically analyzed the interplay between
heterogeneity and buoyant forces, which is shown to control the
migration of the CO2 plume as well as the temporal evolution of
dissolution efficiency. Results show that when buoyant forces are
important, vertical segregation controls the overall behavior of CO2,
diminishing the influence of small-scale heterogeneity on dissolution.
However, when buoyant forces are relatively small compared to the degree
of heterogeneity, CO2 migrates preferentially through high permeability
layers and dissolution efficiency increases with heterogeneity due to
the stretching of the CO2 plume that enhances mixing. As a result, in
this situation, the upscaling of permeability leads to an
underestimation of the dissolution efficiency. A review of field sites
shows that dissolution is heterogeneity-controlled in most real systems.
Knowing that most numerical models cannot afford to represent
heterogeneity at an adequate scale, results indicate that dissolution
efficiency can be typically underestimated by a factor close to 1.5.