Geochemical and mineralogical evaluation of CO2-brine-rock experiments: characterizing porosity and permeability variations in the Cambrian Mt. Simon sandstone

The Cambrian Mount Simon Sandstone has been targeted as a major reservoir for CO2 storage in the Illinois Basin. The Mount Simon Sandstone's geologic setting, mature quartz to arkosic composition, reservoir thickness, and generally low permeability of the overlying Eau Claire Formation seal make it an attractive candidate for long-term storage potential of carbon dioxide. Injection of CO2 has been shown to cause a range of chemical alterations that may causes dissolution of existing minerals and precipitation of secondary phases that can alter the porosity and permeability of the reservoir. This study focuses on conducting detailed microscopic analysis of compositionally and texturally dissimilar Mount Simon Sandstone samples from the Illinois Basin that were experimentally exposed to CO2-rich brines for 6 months at the National Energy and Technology Laboratory in collaboration with the Indiana Geological Survey. Our objective is to examine the experimental samples to determine how porosity texture and mineral abundance influence the types of reactions that occur with CO2 injection at various scales. Petrographic and geochemical analysis coupled with Geochemist Workbench's REACT module demonstrates how porosity and permeability amounts strongly influence rates of mineral precipitation and dissolution that occur over the observed 6-month and projected 1000-year period. These results, which represent the compositional and textural heterogeneities in the formation, provide a set of criterion for evaluating CO2 injection sites and long-term storage potential in the formation.