--> --> Abstract: Seafloor Stability of the Brazilian Continental Margin - Considerations for Offshore Hydrocarbon Exploration and Production, by Marylin P. Segall, Alberto Figueiredo, Gilda M. P. Esteves, and Cleverson G. Silva; #90914(2000)

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Marylin P. Segall1, Alberto Figueiredo2, Gilda M.P. Esteves2, Cleverson G. Silva2
(1) University of Utah, Salt Lake City, UT
(2) Universidade Federal Fluminense, Niteroi, Brazil

Abstract: Seafloor stability of the Brazilian continental margin - considerations for offshore hydrocarbon exploration and production

Near-surface sediments are characterized by unique physical properties that have potentially significant effects on prospect economics related to offshore concessions. Earthquakes, seabed morphology, methane concentrations, near-surface sediment properties and met-ocean dynamics all contribute to conditions that may pose constraints for exploration and development. These parameters affect initial exploration efforts, drilling capability, and eventual recovery.

Five offshore basins are evaluated for physical and environmental features that may have impacts on development: Foz do Amazonas, Cear√°, Potiguar, Sergipe/Alagoas and Espirito Santo. Each basin is characterized by unique antecedent topography and met-ocean conditions inherited from its proximity to the Mid Atlantic Ridge. Evaluation of met-ocean parameters is based on data from buoys, satellite imagery, phytoplankton biomass concentrations and temperature/salinity profiles. Prevailing and local currents with speeds in excess of 100 cm/s are dominant erosional agents on the shelf edge and slope. Destructional processes are evident at points of current divergence.

Continental shelves and upper slopes of the basins are dominated by reworked Holocene and modern sediments. High-resolution seismic profiles of shelf-originating canyons indicate basinal deposits are derived from catastrophic failure on the slope through gravity flows, creep, undercutting and turbidity currents. Slope-originating canyons form where gradients are the steepest and where primary currents diverge; turbidity-current deposits comprise the lower slope and basin seaward of these canyons. Reverse (i.e., upslope) currents created by topographic highs associated with diapirs undercut lower slope sediments in salt basins.

Thickness of unconsolidated sediments within the basins is variable; however, differences in lithology/degree of consolidation, migrating oceanic currents and displaced sediment packages result in sequences of foundation materials with non-uniform strength profiles. Integrated characterizations of environmental data and sediment properties are necessary components of a comprehensive basin evaluation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana