Implications of Coupling Fractional Flow and Geochemistry for CO2 Injection in Aquifers

Abstract

Summary The geochemical changes caused by carbon dioxide (CO2) injection into aquifers include acidification and carbonation of the native brine. There are also potential mineral-dissolution and mineral-precipitation reactions caused by the aqueous-composition changes. The latter are important for evaluating the potential CO2-storage capacity in the form of minerals. Reactions also may influence the performance of the injection well. The theories of geochemical flows and of fractional flow provide useful insight into several aspects of CO2 sequestration. This paper gives the mathematical formalism of combined geochemical reactions and multiphase flow. If the local-equilibrium assumption applies, the theory leads to a graphical solution, from which it is easy to see when and under what conditions mineralization will occur. The theory also illustrates the modes of CO2 trapping (hydrodynamic, solubility, mineral, residual saturation). Trapping mechanisms are identified analytically. We also show that the natural groundwater flow alters the modes of trapping significantly.