Numerical Analysis of the Effect of Heterogeneity on CO2 Dissolution
Enhanced by Gravity Driven Convection
Abstract
Dissolution trapping of CO2 in brine can reduce the risk of leakage of
supercritical CO2 during long-term Geological Carbon Sequestration
(GCS). The dissolution of overlying gaseous CO2 into brine increases the
density of brine in its upper portion, which causes gravity-driven
convection (GDC) and thus significantly increases the rate of CO2
dissolution. To date, most studies on GDC-driven dissolution are based
on homogeneous media and only few studies exist on the effect of
heterogeneity on GDC-driven dissolution. Here, we study the effect of
heterogeneity on GDC-driven dissolution rate by using numerical
simulations with randomly obtained permeability fields. Dissolution
rates calculated by these simulations are related to properties of the
permeability field by using least-squares regression. We obtained two
empirical formulas for predicting the asymptotic GDC-driven dissolution
rate. In the first formula the dissolution rate is almost linearly
proportional to the dimensionless equivalent vertical permeability. In
the second one the dissolution rate is linearly proportional to a
dimensionless vertical finger-tip velocity. Both formulas show a
non-linear relation between dissolution and anisotropy with higher
anisotropy giving lower dissolution rates.