SEQUESTERING CARBON DIOXIDE WITHIN THE UPPER CRETACEOUS TUSCALOOSA GROUP OF THE US GULF COAST: COMPOSITION AND GEOCHEMICAL ANALYSIS

The Tuscaloosa Group is a thick sandstone and shale deposit that spans much of the Cenomanian-Turonian interval. Regionally, the Tuscaloosa Group is commonly subdivided into a sandy unit called the lower Tuscaloosa, a middle unit called the Marine Tuscaloosa shale, and a variegated sandstone-mudstone interval called the upper Tuscaloosa. The sands of the lower Tuscaloosa locally have porosity greater than 30% and permeability exceeding 16 D. The sandy portion of the Tuscaloosa (8 to 80 m thick) is composed primarily of poorly sorted, fine- to coarse-grained, cross-bedded and ripple-bedded sandstone. The sandstone is primarily sublitharenite and can range in composition between subarkoses and lithic subarkose. Modal analysis and whole-rock geochemical analysis suggests that the Tuscaloosa is highly weathered and thus has a high chemical index of alteration; its provenance is dominated by felsic plutonic rocks, including upper-grade metamorphic and metasedimentary sequences of the Inner Piedmont terrain of the southern Appalachians.

Tuscaloosa petrology is mainly clay-rich immature sands of braided fluvial, lacustrine, and heterolithic tidal origin. The Marine shale is a regional reservoir seal, and the saline formation water makes lower Tuscaloosa sandstone an ideal storage target. The chalk of the Selma Group and the mudstone of the overlying Porters Creek Clay are more than 600 m thick and add additional sealing security. Considering the depth and thickness of the lower Tuscaloosa Group, its petrology, and its vast lateral extent within the Gulf Coast geological province, the Tuscaloosa is an excellent target for injected storage of carbon-dioxide, and it has multi-gigatonne storage capacity.