AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Carbon Sequestration in the South Georgia Rift: Is the Ubiquitous "J" Reflection Synonymous with Basalt?
(1) Earth and Ocean Sciences, University of South Carolina, Columbia, SC.
(2) Earth Sciences and Resources Institute, University of South Carolina, Columbia, SC.
The South Georgia Rift (SGR) basin, a Triassic rift basin buried beneath the Coastal Plain of South Carolina, Georgia, Alabama, and Northern Florida, recently has received interest as a potential site for carbon sequestration. Several aspects make the SGR appealing, these include size, burial depth, lack of numerous deep exploration holes, and a presumed thick layer of basalt covering the majority of the basin. The areal extent of this basalt layer has been based on the seismic character of a high-amplitude, two-cycle reflection and is referred to as the “J” reflector which corresponds with the Jurassic Club House Crossroads basalt encountered in a test well near Summerville, SC. Recent analysis of seismic and nearby well data, however, calls into question the interpretation of the “J” reflector as being synonymous with basalt.
COCORP seismic surveys collected in western Georgia show a prominent reflector at the base of a subhorizontal, seaward-thickening reflection package that unequivocally corresponds to the Coastal Plain. The prominent basal reflector can be traced along COCORP Georgia Line 21 (GA-21) to the North and extrapolated to intersect the Fall Line at time 0. This same reflector also can be mapped on GA-10, 11, 12, 13, 14, 19, and 20. Previous workers interpreted this reflector to be the “J” reflector on GA-10, 11, 12, and 13 and proposed a different reflector as the base of the Cretaceous Coastal Plain. Reexamination of the well correlations, however, demonstrates this to be an unlikely scenario. Additionally, more recent well data have been examined and synthetic seismograms generated to better characterize the nature of the “J” reflection.
Our conclusion is that the “J” reflection is the result of the acoustic impedance contrast between the base of the low-velocity, unconsolidated Coastal Plain sediments and the higher-velocity and denser material beneath. This interpretation does not indicate that the SGR is no longer a viable reservoir for geologic sequestration of carbon dioxide, just that the regional extent of other potential seals, such as shales or diabase sills, will need to be carefully evaluated.