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Multi-Zone Carbon Storage Potential in Cretaceous Saline Reservoirs of the Gulf Coast Basin, Southwest Alabama

Pashin, Jack 1; McIntyre, Marcella 1; Grace, Rashmi 1; Hills, Denise 1; Esposito, Richard A.2; Koperna, George 3; Petrusak, Robin L.3
1 Geological Survey of Alabama, Tuscaloosa, AL.
2 Southern Company Generation, Birmingham, AL.
3 Advanced Resources International, Arlington, VA.

The eastern part of the Gulf Coast Basin in southwest Alabama contains a succession of Mesozoic-Cenozoic sedimentary rocks ranging in thickness from 4 to 6 km. This succession is dominated by sandstone and shale and also includes carbonates and evaporites. Coal fired power plants in this area emit more than 15 Mt of CO2 annually, and strata in the Mesozoic section were characterized to determine the feasibility of permanent geologic storage of these emissions.

Saline reservoirs suitable for safe, long-term geologic storage of CO2 were identified in a multitude of Cretaceous-age sandstone units between depths of 1,250 and 4,000 m with additional capacity existing in older formations. These strata accumulated in diverse terrestrial through marginal-marine environments, forming a wedge of sediment that thickens southwestward toward the Gulf of Mexico. Subsurface mapping indicates that a large volume of reservoir-quality sandstone is available for CO2 storage from the base of the Paluxy Formation to the top of the Eutaw Formation. Mean porosity is 24.8 percent, and mean is permeability higher than 210 mD, thus indicating high capacity and injectivity.

Major geologic structures in the study area include the Mobile Graben, an associated series of faulted anticlines, and a series of salt-cored anticlines to the west of the graben. Fault juxtaposition of permeable strata within the Cretaceous-Tertiary section indicates that the faulted anticlines are not ideal storage sites. A nearly flat-lying structural panel west of the graben, by contrast, is highly prospective for long-term CO2 storage. Moreover, some salt-cored anticlines west of the graben form four-way structural closures with high storage potential.

Underground sources of drinking water are typically shallower than 2,000 feet and are limited to the Cenozoic section in the study area. Multiple shale and chalk seals, moreover, have regional extent and separate these drinking water sources from the storage interval. Clustered sandstone units in the upper part of the Washita-Fredericksburg interval and the Lower Tuscaloosa Group provide an excellent opportunity to maximize storage capacity in a narrow stratigraphic interval. With capacity in the Paluxy-Eutaw interval estimated between 20 and 40 Mt/mi2 at only 10 percent storage efficiency, it is clear that Cretaceous strata in southwest Alabama can support commercial sequestration operations at the millennial scale at current emission rates.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009