RESOURCES FOR GEOLOGIC CARBON SEQUESTRATION IN THE STATE OF GEORGIA: POTENTIAL AND PITFALLS IN THE PALEOZOIC RIDGE AND VALLEY, THE MESOZOIC SOUTH GEORGIA RIFT BASIN, AND THE MESO-CENOZOIC COASTAL PLAIN

Permanent storage of captured CO₂ is an important component of strategies to avoid the worst impacts of anthropogenic climate change. Safe, efficient, and effective sequestration will be crucial to the U.S. energy economy, creating substantial demand for sealed pore space. Potential reservoirs for injection must have 1) substantial, permeable pore space; 2) P-T conditions keeping CO₂ as a supercritical fluid; and 3) impermeable overlying seals. Additional criteria include proximity to CO₂ capture sites, (i.e. power plants) and added value in enhanced oil or coalbed methane recovery.

Three potential Georgia reservoir regions are 1) Paleozoic strata; 2) Mesozoic rift basin fill; and 3) passive margin Coastal Plain deposits. In the Ridge and Valley, the lower Paleozoic section extends to sufficient depth, including the Cambrian Weisner Quartzite, Shady Dolomite, and the Conasauga Group. The Weisner has coarse facies capped by shales and recrystallized dolomite, but significant lateral facies changes are observed. Moreover, it is locally recrystallized to massive quartzite and is intensely faulted.

In the South Georgia Rift, lacustrine mudstones, sills, and lavas provide excellent confining layers. Coarse facies occur near border faults; these were sampled by Savannah River Site cores (Chowns et al., 1996). Thin sections and XRD of these arkosic conglomerates and sandstones exhibit silica and albite feldspar diagenetic cements, similar to those in other Newark Supergroup basins. Unless other areas of the basin escaped high temperature diagenesis, it is unlikely that the rift sediments have pore space sufficient for CO₂ injection.

Coastal Plain geophysical well logs suggest at least two regional reservoirs in the Georgia equivalent of the Tuscaloosa Formation, both capped by maximum flooding surfaces. Coarse sediment is also abundant in the undifferentiated Lower Cretaceous sediment, but confining units are not extensive. Stratigraphic architecture of the Georgia coastal plain is similar to other passive margin settings, including the Gulf Coast, but the absence of petroleum and natural gas reserves hints at poor regional seals. Nonetheless, if seal integrity can be demonstrated, Cretaceous sediments in Georgia likely hold the greatest potential in the state for carbon injection and storage.