MONITORING CARBONATE PRECIPITATION AND DISSOLUTION DUE TO ELEVATED CO2 IN GROUNDWATERS

Protecting subsurface groundwater is an important component of carbon capture and sequestration (CCS) risk assessment. Reactive transport modeling and simulations can anticipate expected geochemical transformations due to CO₂ leaks within a given aquifer, but field experiments are still necessary to critique model predictions and to document in situ reaction rates. Geological formations associated with storage sites may include a wide range of reactive silicate, oxide, oxyhydroxide, carbonate, and sulfide minerals, and the stability of these minerals may be affected when aqueous chemical equilibria are modified by leaking CO₂. In this study, we propose the use of laser-induced breakdown spectroscopy (LIBS) to monitor the precipitation and dissolution of carbonate minerals in the presence of CO₂. The technique has successfully been used to conduct laboratory-scale experiments to measure calcium and other cations in aqueous samples. Stability fields for a wide range of carbonate minerals over a pH range of 5-8 were determined by geochemical modeling. Experiments using ICP analysis detected changes in dissolved divalent ions due to precipitation and dissolution reactions when CO₂ gas was added incrementally. The aim of this research is to develop a method for in situ monitoring of CO₂ leakage into groundwater aquifers.