POTENTIAL FOR CARBON SEQUESTRATION IN THE SUBSURFACE TUSCALOOSA GROUP, SOUTHWESTERN ALABAMA

Glauconitic sands, sometimes referred to as greensand formations, are associated with continental shelf sediments typically deposited during Cambrian, Cretaceous, and Cenozoic strata. Previous studies suggest that they may be adequate reservoirs for geologic CO₂ storage. In this project, the Upper Cretaceous Tuscaloosa Group of the subsurface of southwestern Alabama is the geological unit analyzed for carbon sequestration purposes. The Tuscaloosa Group has an overall subsurface thickness of 183-369 m on the west of Alabama, and an approximate porosity of 25%. An essential part of this study was to observe and explore how the injected CO₂ fluid interacts with porous rocks, specifically with the mineral glauconite, and what type of pore occurring cement develops, and how does it change the porosity of the rocks. Samples from the drill core Julian F. McGowin No. 1. were collected for observing lithological changes, sedimentary structures and textures, vertical changes in grain size and mineralogy, as well as measuring porous thickness. Petrographic thin sections, as well as core observations, show evidence of glauconite throughout most of the core. XRD results show the mineralogical bulk composition of mostly quartz, glauconite, muscovite, K-feldspar, chlorite, and illite. An experimental plan for a hydrothermal experiment was made using brine data collected from the Geological Survey of Alabama. Upper Cretaceous brine is mostly composed of Na-Ca-Cl, with high concentrations of Mg. This part of the experiment took place inside a rocking autoclave apparatus, and the software Geochemist's Workbench was used to analyze the reaction path. According to previous studies, the Tuscaloosa Group qualifies as a near-limitless reservoir for storing CO₂ because of its composition, porosity, permeability, and depth. Based on observations made so far, the supercritical CO₂ fluid will not negatively affect the glauconitic sands. However, it is important to study and analyze carbon sequestration's effects before injecting any CO2 into any formation.