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GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 50 (2000), Pages 495-503

Surface Amplitude Mapping of 3D-Seismic for Improved Interpretations of Seafloor Geology and Biology from Remotely Sensed Data

Harry Roberts, James Coleman; Jesse Hunt, Jr., W.W. Shedd

Abstract

For the first time, the complex continental slope opposite Louisiana is covered with a high quality data base, other than bathymetry (multibeam), for interpreting seafloor geology. This data base consists of large adjacent and overlapping tracks of 3D-seismic data. The Minerals Management Service (MMS), in cooperation with university personnel, is utilizing these reasonably uniform data in conjunction with other supporting data sets to help improve interpretation of seafloor geology and biology for regulatory purposes. Of particular interest is the reliable identification of (a) geohazards associated with areas of fluid and gas expulsion, and (b) sites of lawfully protected chemosynthetic communities. Initial results indicate that 3D-seismic surface amplitude data calibrated to high resolution acoustic data, as well as direct seafloor observations and samples, is a powerful predictor of surficial geology and to a lesser extent biology of the slope. Surface amplitude data can determine hard lithified bottom as compared to soft gas-charged surface and near-surface sediments. Faults, fault trends, and some mass movement features are also imaged by surface amplitude data. Correlation of surface amplitude data with known sites of chemosynthetic communities located and mapped under MMS-sponsored research indicates that water bottom amplitudes suggesting gas-charged sediments correlate with the occurrence of chemosynthetic organisms. Observational data from manned submersibles suggest that the occurrence of these communities correlates with gas hydrates at the seafloor or in the very shallow subsurface. Additionally, there is a high degree of correlation between the location of the water bottom amplitude anomalies and the location of proven hydrocarbon trapping faults that cut the water bottom. Of the 83 fields studied in the deep water Gulf of Mexico to date, all 60 that are trapped by faults that cut the water bottom have variable strength seafloor amplitude anomalies associated with them. Those fields that do not have amplitude anomalies associated with them are either stratigraphically trapped, subsalt accumulations, or trapped by buried faults. Over the next 3-years, this MMS-funded research program is designed to establish improved links between remotely sensed 3D-seismic surface amplitude data and actual seafloor conditions so that amplitude data can be used as a reliable predictor of surficial geology-biology of the northern Gulf continental slope.


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