Numerical Modeling Studies of The Dissolution-Diffusion-Convection ProcessDuring CO2 Storage in Saline Aquifers Page: 1 of 33
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Numerical Modeling Studies of The Dissolution-Diffusion-Convection Process
During C02 Storage in Saline Aquifers
Karsten Pruess and Keni Zhang
Earth Sciences Division, Lawrence Berkeley National Laboratory
University of California, Berkeley, CA 94720, U.S.A.
For purposes of geologic storage, C02 would be injected into saline formations at supercritical
temperature and pressure conditions, and would form a separate phase that is immiscible with the
aqueous phase (brine). At typical subsurface temperature and pressure conditions, supercritical
C02 (scCO2) has lower density than the aqueous phase and would experience an upward
buoyancy force. Accordingly, the C02 is expected to accumulate beneath the caprock at the top
of the permeable interval, and could escape from the storage formation wherever (sub-)vertical
pathways are available, such as fractures or faults through the caprock, or improperly abandoned
wells. Over time, an increasing fraction of C02 may dissolve in the aqueous phase, and
eventually some of the aqueous C02 may react with rock minerals to form poorly soluble
carbonates. Dissolution into the aqueous phase and eventual sequestration as carbonates are
highly desirable processes as they would increase permanence and security of storage.
Dissolution of C02 will establish phase equilibrium locally between the overlying C02 plume
and the aqueous phase beneath. If the aqueous phase were immobile, C02 dissolution would be
limited by the rate at which molecular diffusion can remove dissolved C02 from the interface
between C02-rich and aqueous phases. This is a slow process. However, dissolution of C02 is
accompanied by a small increase in the density of the aqueous phase, creating a negative
buoyancy force that can give rise to downward convection of C02-rich brine, which in turn can
greatly accelerate C02 dissolution. This study explores the process of dissolution-diffusion-
convection (DDC), using high-resolution numerical simulation. We find that geometric features
of convection patterns are very sensitive to small changes in problem specifications, reflecting
self-enhancing feedbacks and the chaotic nature of the process. Total C02 dissolution rates on
the other hand are found to be quite robust against modest changes in problem parameters, and
are essentially constant as long as no dissolved C02 reaches the lower boundary of the system.
17 November 2008
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Pruess, Karsten & Zhang, Keni. Numerical Modeling Studies of The Dissolution-Diffusion-Convection ProcessDuring CO2 Storage in Saline Aquifers, report, November 17, 2008; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc898341/m1/1/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.