Experimental
Determination of Reaction Rates and Modeling of the Long-Term Fate of CO2 in
Deep Geological Formations
Lu, Peng1, Qi
Fu2, William E. Seyfried2, Brain R. Strazisar3,
Sheila W. Hedges3, Zuoping Zheng1,
Chen Zhu1 (1) Department of Geological Sciences, Indiana University,
Bloomington, IN (2) Department of Geology and Geophysics, University of
Minnesota, Minneapolis, MN (3) National Energy Technology Laboratory, U.S.
Department of Energy, Pittsburgh, PA
The injection of CO2 into deep saline
aquifers is a potential option for greenhouse gas mitigation. However, several
key issues, such as underground storage time and the fate of the injected CO2,
must be studied before this option becomes economically and socially
acceptable. In order to the feasibility of CO2 injection, we conducted feldspar
dissolution experiments in CO2 impregnated brines. Feldspars dissolution rates
were calculated based on temporal change in solution chemistry. Analysis of
mineral reactants (SEM, TEM and XPS) following the experiments confirmed the
existence of abundant secondary mineralization associated with feldspar
surfaces. The reaction path and secondary minerals precipitation kinetics were
determined by reaction-path modeling. The slow kinetics of secondary minerals exert a strong control of feldspar dissolution. The
experimental work was supplemented with one-dimensional reactive mass-transport
modeling. The dissolution of the injected CO2 into brine causes a sharp drop in
pH, and consequently, the acidic brine aggressively reacts with aquifer
minerals. Our model also predicts the dissolution of aluminosilicate
minerals with the formation of secondary minerals and the precipitation and
dissolution of carbonate minerals and is consistent with laboratory-scale CO2
core-flooding experiments in the literature. The transport of carbon can be
significantly retarded with respect to the flow of the brine itself, and a
significant amount of injected CO2 is immobilized because of mineral trapping.
The carbon reactive transport is sensitive to the reaction rates used,
illustrating the need for improved knowledge of reaction kinetics.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California