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.