Carbon Dioxide (CO2) Dissolution Efficiency During Geological Carbon Sequestration (GCS) in Randomly Stratified Formations

Geological carbon sequestration mitigates climate change by capturing and storing carbon dioxide (CO2) emissions in deep geologic formations. Dissolution trapping is one mechanism by which CO2 can be trapped in a deep formation. However, heterogeneity can significantly affect the 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 (sigma(2)(Y) ) and gravity factor (G), which is shown to control the migration of the CO2 plume as well as the temporal evolution of dissolution efficiency. Results show that when G is important, vertical segregation controls the overall behavior of CO2 , diminishing the influence of small-scale heterogeneity on dissolution. However, when G is relatively small compared to sigma(2)(Y), CO2 migrates preferentially through high permeability layers and dissolution efficiency increases with sigma(2)(Y) 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.