--> The Paluxy Formation in the East-Central Gulf of Mexico Basin: Geology of an Ultra-Giant Anthropogenic CO2 Sink

AAPG ACE 2018

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The Paluxy Formation in the East-Central Gulf of Mexico Basin: Geology of an Ultra-Giant Anthropogenic CO2 Sink

Abstract

The Paluxy Formation in Alabama, Mississippi, and the adjacent continental shelf constitutes a widespread succession of sandstone and shale that has proven to be one of the most important targets for geologic CO2 storage in the east-central Gulf of Mexico Basin. An integrated analysis of stratigraphy, sedimentology, and reservoir properties based on cores and geophysical well logs indicates that the Paluxy presents multiple Gt storage opportunity. Activities 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 and in east-central Mississippi as part of the ECO2S CarbonSAFE Project at the Kemper Energy Facility have established the potential for safe, permanent CO2 storage in the Paluxy Formation.

Paluxy strata are of Early Cretaceous age and are dominated by variegated sandstone and mudstone units that form a thick (200-300 m) redbed succession. The Paluxy sharply overlies the mudstone-dominated Mooringsport Formation and is overlain by the basal mudstone unit of the Washita-Fredericksburg interval. The Paluxy is composed of stacked, fining-upward sandstone-mudstone packages that are typically between 12 and 25 m thick. Depositionally, the sandstone units represent sandy bedload-dominated fluvial deposits, and the mudstone units represent interfluvial deposits, including vertic paleosols that formed under semi-humid to semi-arid conditions. The fining-upward sandstone-mudstone packages form aggradational to progradational sequence sets of complexly stacked reservoir units. Sequence frequency is on the order of 100 ky, suggesting sedimentation on an extensive sandy braidplain that was influenced by Milankovitch short eccentricity.

Core analysis of Paluxy sandstone indicates that porosity averages 23% and is locally >30%. Permeability locally exceeds 3,800 mD and has a geometric mean of 220 mD. The P50 capacity of the Paluxy commonly is on the order of 2 Mt/km (5 Mt/mi2), and the reservoir interval has areal extent of about 190,000 km2 (75,000 mi2), indicating an unscreened capacity of 380 Gt of CO2. Accordingly, the Paluxy presents an ultra-giant CO2 storage objective, and multiple baffles, barriers, and a thick topseal indicate commercial potential over large areas of the east-central Gulf of Mexico Basin.