Geochemical evaluation of Washita-Fredericksburg formation as a carbon storage reservoir.

Geological carbon sequestration is a promising technique to reduce atmospheric greenhouse gas emissions. The Washita-Fredericksburg formation in the southeastern United States is being considered as a prospective storage formation. This requires understanding the geochemical impact of CO2 injection on the formation, which is the focus of this work. Here, sandstone samples from the Washita-Fredericksburg formation are analyzed to understand their overall mineralogical composition and the potential geochemical processes that might occur following CO2 injection. Powder X-ray diffraction (XRD) analysis, Scanning Electron Microscopy (SEM) imaging, and image analysis were used to identify mineral phases. SEM images were processed to create a segmented mineral map, which was then used to calculate mineral volume fractions and porosity. Results show that the sample has a porosity of 20% and is mainly composed of quartz, K-feldspar, muscovite, and clays. Accessory minerals such as titanite were also found. Reactive transport models were constructed to assess potential CO2-brine-mineral interactions following CO2 injection. Simulation results suggest that the overall extent of mineral dissolution and precipitation reactions over 10,000 days is limited, with muscovite dissolution increasing porosity to 22%. Limited mineral reactions suggest more injected CO2 will exist in free and dissolved forms, which may require more extensive long-term monitoring.