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Geological Characterization for CO2 Storage in Cretaceous Sandstone Kemper County Energy Facility, Kemper County, Mississippi


The Paluxy Formation and Tuscaloosa Group in the eastern Gulf of Mexico Basin constitute a widespread succession of sandstone and shale that presents a multi-gigatonne storage opportunity for anthropogenic CO2. Sealing strata, baffles, and barriers to flow include mudstone units in the Washita-Fredericksburg interval and the Tuscaloosa Group. Scanning electron microscopy coupled with energy dispersive spectroscopy analysis is widely used to characterize shale as a petroleum source rock and reservoir rock, but little work has been published evaluating mudstones as confining layers in CO2 storage complexes. Scanning electron microscopy and energy dispersive spectroscopy are being used to characterize microfabric, mineralogy, and pore systems within mudrocks at the Kemper County Energy Facility. Characterization has two-fold importance: (1) to characterize free and adsorbed storage potential and (2) to characterize potential migration of CO2 molecules into mudstone baffling layers and seals by capillary processes and diffusion, which can ultimately result in leakage from the primary injection targets. Mudstone in the Tuscaloosa Group supports free storage in interparticle pores as well as adsorption on organic matter and smectitic clay surfaces. Mudstone in the Paluxy Formation and Washita-Fredericksburg interval lacks significant organic matter, and so most adsorption is on clay. High water saturation in the Cretaceous mudstone units helps keep capillary entry pressure high, and mudrock permeability is on the order of 1 nD. These low permeability values indicate that the mudrock units are effective baffles, barriers, and seals and that slow permeation of the mudrock pore systems makes significant migration of injected CO2 out of the storage complex unlikely.