--> Abstract: Sedimentologic Characterization of Santos Basin Gas Reservoirs: Shallow- and Deep-Marine Siliciclastic Depositional Systems Related to Hyperpycnal Flows (Brazil Deep Seds - Deep-Water Sedimentation on the Southeast Brazilian Margin Project), by Roberto S.F. D'Avila, C.V. Madeira, J.L.P. Moreira, S.F. Santos, and D.C. Dias Filho; #90039 (2005)

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Sedimentologic Characterization of Santos Basin Gas Reservoirs: Shallow- and Deep-Marine Siliciclastic Depositional Systems Related to Hyperpycnal Flows (Brazil Deep Seds - Deep-Water Sedimentation on the Southeast Brazilian Margin Project)

Roberto S.F. D'Avila, C.V. Madeira, J.L.P. Moreira, S.F. Santos, and D.C. Dias Filho
Petrobras, Rio de Janeiro, Brazil

The sedimentological characterization of gas-prone Santos Basin upper Cretaceous turbidite systems was obtained from 3D-seismic attribute maps, well logs cores and biostratigraphic data. Cores from Santonian and Campanian sand-rich turbidite systems are characterized by metric normal graded beds of compositional/textural immature sands.

The most common facies are: thin beds of conglomerates; massive or cross-stratified very poorly sorted coarse-grained sands; faintly laminated or massive very poorly sorted fine-grained sands; poor to well sorted with ripples fine-grained sands; heterolitic facies of thin bedded shale/siltstone and fine-grained sand with ripples; and, bioturbated pelitic beds.

This facies association is related to moderate to low efficient flows, where the most frequent facies are very poorly sorted sands independently of the modal granulometric class. The great amount of charge structures and post-depositional fluidization features suggests both high deposition rate and high frequency of these flows.

The hyperpicnal origin of these flows has been recognized based on: stratigraphic association with fluvial-deltaic systems; coal fragments; immature sands; traction features in the sandy/conglomeratic beds; and, alternate granulometric coarsening and fining without any evident boundary, which would indicate surge type flow. Despite their similar facies association, the studied Santonian and Campanian turbidite systems are very distinct. They differ in terms of: thickness of the sand package; paleogeographic setting (shelf vs. slope/basin); size of coalescent fans; feeding system (multiple shallow channels vs. single deeply incised canyons); and, eustatic/tectonic vs. halokinetic control.

 

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005