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Geologic Framework of an Anthropogenic Carbon Capture and Sequestration System at the Kemper County Energy Facility, East-Central Mississippi

Abstract

AAPG ACE 2019 - San Antonio, TX

Theme 6: Energy Sustainability and the Environment

Geologic Framework of an Anthropogenic Carbon Capture and Sequestration System at the

Kemper County Energy Facility, East-Central 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. Geologic characterization of these strata at the Kemper County Energy Facility in

east-central Mississippi as part of the U.S. Department of Energy’s CarbonSAFE program focuses on

delineating the stratigraphic framework with an emphasis on reservoir and seal analysis. Core studies in

conjunction with petrophysical well-log analyses from three exploration wells have yielded a high

resolution stratigraphic characterization of the targeted CO2 storage reservoirs, baffles, and seals. The

porosity of Cretaceous sandstone averages 30 percent, and permeability is locally as high as 16,000 mD.

Sealing strata, baffles, and barriers to flow include mudstone units in the Washita-Fredericksburg

interval and the Tuscaloosa Group.

SEM coupled with EDS 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. SEM and EDS 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. Entry of supercritical CO2 into the mudrock units greatly reduces

water saturation, and drying ultimately raises permeability by an order of magnitude. 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.