Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Earth and Ocean Sciences

Sub-Department

Geology

First Advisor

Camelia C Knapp

Abstract

The Triassic-Jurassic South Georgia Rift (SGR) basin, buried beneath Coastal Plain sediments of southern South Carolina, southeastern Georgia, western Florida, and southern Alabama, consists of an assemblage of continental rift deposits (popularly called red beds), and mafic igneous rocks (basalt flows and diabase sills). The red beds are capped by basalts and/or diabase sills, and constitute the target for supercritical CO2 storage as part of a Department of Energy funded project to study feasibility for safe and long-term sequestration. This study addresses key stratigraphic, structural and petrophysical issues critical to determine subsurface suitability for CO2 storage as well as improved understanding of the Triassic basin's evolution and underline characteristics. Also unlike shale-capped CO2 reservoirs, very little is known about the ability of basalts and diabase sills to act as viable seals for CO2 storage.

New interpretations from reprocessed SeisData6 Coastal Plain, supported by analysis of well data, substantiate the presence of a buried Triassic basin in South East Georgia that is about 2.2 km deep and 170 km wide. It appears to coincide with the subsurface convergence of the southwest and northeast extensions of the Riddleville and Dunbarton basins that are subsidiaries of the main SGR basin. Contrary to previous study, this basin does not have basalt. Our data show no clear evidence for the Augusta fault that was identified in other studies in the vicinity of the Piedmont-Coastal Plain boundary in Georgia and South Carolina. Petrophysically, the SGR basin manifests distinct porosity-permeability regimes that are influenced by the depositional environments. New results also indicate the presence of thick, confined porous red beds with average porosity as high as 14%. However, the red beds' permeability is generally low and shows large numerical variations both locally and regionally. Low permeability is caused by poor sorting, small pore throats and tectonically induced compaction and diagenesis. Changes in porosity and permeability with depth are highly significant within the SGR basin, and suggest a compacted basin with a history of uplift and erosion. Analyses further show that the basalt flows and diabase sills in the southern South Carolina part of the SGR possess low porosity, high seismic velocity, and density that are favorable to caprock integrity.

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Geology Commons

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