Premium
Two‐phase convective CO 2 dissolution in saline aquifers
Author(s) -
Martinez M. J.,
Hesse M. A.
Publication year - 2016
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2015wr017085
Subject(s) - dissolution , convection , brine , saturation (graph theory) , convective mixing , mass transfer , boundary layer , permeability (electromagnetism) , materials science , geology , mineralogy , thermodynamics , chemistry , chromatography , biochemistry , physics , mathematics , combinatorics , membrane
Geologic carbon storage in deep saline aquifers is a promising technology for reducing anthropogenic emissions into the atmosphere. Dissolution of injected CO 2 into resident brines is one of the primary trapping mechanisms generally considered necessary to provide long‐term storage security. Given that diffusion of CO 2 in brine is woefully slow, convective dissolution, driven by a small increase in brine density with CO 2 saturation, is considered to be the primary mechanism of dissolution trapping. Previous studies of convective dissolution have typically only considered the convective process in the single‐phase region below the capillary transition zone and have either ignored the overlying two‐phase region where dissolution actually takes place or replaced it with a virtual region with reduced or enhanced constant permeability. Our objective is to improve estimates of the long‐term dissolution flux of CO 2 into brine by including the capillary transition zone in two‐phase model simulations. In the fully two‐phase model, there is a capillary transition zone above the brine‐saturated region over which the brine saturation decreases with increasing elevation. Our two‐phase simulations show that the dissolution flux obtained by assuming a brine‐saturated, single‐phase porous region with a closed upper boundary is recovered in the limit of vanishing entry pressure and capillary transition zone. For typical finite entry pressures and capillary transition zone, however, convection currents penetrate into the two‐phase region. This removes the mass transfer limitation of the diffusive boundary layer and enhances the convective dissolution flux of CO 2 more than 3 times above the rate assuming single‐phase conditions.