Conn L. Wethington, Jack Pashin, Oklahoma State University, Jamar Bynum, Baker Hughes
The Cretaceous and Tertiary deposits in Alabama, Mississippi, and the adjacent continental shelf constitutes a widespread succession of sandstone, mudstone, and carbonate that have proven to be important targets for geologic CO₂ storage in the onshore Gulf of Mexico basin. An integrated analysis of stratigraphy, sedimentology, and reservoir properties based on cores and geophysical well logs indicates that the Paluxy Formation and Washita-Fredericksburg interval present a gigatonne-class storage opportunity in east-central Mississippi. Previous research sponsored by the U.S. Department of Energy and the Southern States Energy Board in south Alabama as part of the SECARB Anthropogenic test established the Paluxy Formation as a safe and permanent carbon storage objective. The knowledge gained at Citronelle Field is being transferred to east-central Mississippi as part of the ECO₂S CarbonSAFE project at the Kemper County Energy Facility. Geologic characterization of the Mississippi Embayment at the energy facility has focused primarily on characterizing the depositional framework with an emphasis on storage complex definition. Integration of core analyses and geophysical well logs has yielded a high-resolution analysis of the targeted CO₂ storage reservoirs, baffles, barriers, and seals. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), and quantitative X-ray diffraction (XRD) was used to characterize microfabric, pore types, and mineralogy within mudstone at the Kemper County Energy Facility. This characterization has two-fold importance: (1) characterizing the storage resource and (2) characterizing the quality and behavior of mudstone baffles, barriers, and seals in the subsurface. High water saturation in the upsection Cretaceous mudstone units helps keep capillary entry pressure high, and mudrock permeability is on the order of 10’s nD. These low permeability values indicate that the mudstone units are effective confining intervals and seals that make significant migration of injected CO₂ out of the storage complex unlikely. A combination of free storage and organic-clay adsorption in the mudstone units has potential to trap any fugitive CO₂ that may migrate from the primary sandstone storage objectives, and the thick succession of sealing strata helps ensure the security of the storage complex