Mudstone characterization at a world-class CO2 storage site: Kemper County Energy Facility, Kemper County, Mississippi

Abstract

The Cretaceous and Tertiary deposits in Alabama, Mississippi, and the adjacent continental shelf constitutes a widespread succession of sandstone and shale that have proven to be an important target for geologic CO2 storage in the onshore Gulf Coast basin. An integrated analysis of stratigraphy, sedimentology, and reservoir properties based on cores and geophysical well logs indicates that the Paluxy Formation, Washita-Fredericksburg interval, and the Lower Tuscaloosa Group present a gigatonne-class storage opportunity. 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 in the Citronelle Field established the Paluxy 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 Kemper County Energy Facility focused primarily on delineating a stratigraphic framework with an emphasis on seal-rock analysis. Integration of core analyses and geophysical well logs has yielded a high-resolution stratigraphic analysis of the targeted CO2 storage reservoirs, baffles, barriers, and seals. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) was used to characterize microfabric, mineralogy, and pore types within mudstone of the east-central Mississippi Embayment at the Kemper County Energy Facility. This characterization has two-fold importance: (1) to characterize free and adsorbed storage potential and (2) to characterize potential migration of CO2 into mudstone baffling layers and seals by capillary processes and diffusion, which promote leakage from the primary injection targets. Mudstone in the Tuscaloosa Group supports adsorption and free storage in organic matter and smectitic mudrock. Mudstone in the Paluxy Formation and Washita-Fredericksburg interval lacks significant organic matter, and free storage and adsorption is in mudrock. High water saturation in the Cretaceous mudstone units helps keep capillary entry pressure high, and mudrock permeability is on the order of 1-100 nD. These low permeability values indicate that the mudstone units are effective baffles, barriers, and seals that make significant migration of injected CO2 out of the storage complex unlikely.