Basin Floor Paleotopography: A Major Control on Reservoirs in Santos, Campos and Espirito Santo Basins, Brazil (BRazil Deep Seds - Deep-Water Sedimentation on the Southeast Brazilian Margin Project)

Almerio B. França, A. P. France, E. J. Milani, and A. R. Viana
Petrobras, Rio de Janeiro, Brazil

The Brazilian petroleum reserves in Dec-2003 are 12.6 billion barrels of oil-equivalent. About 90% is located in Campos and Espírito Santo basins. More than 90% of that is accumulated in turbidites and turbidite-like deposits of Cretaceous and Tertiary time.

A flat ocean bottom where deep-water turbiditic currents deposited broad submarine fans is the very first image one might have for the sand-prone offshore basins in Brazil. This image does not apply for most of the reservoirs in Campos, Santos and Espírito Santo basins. On the contrary, paleotopography was rather hilly, chiefly because of the structural framework of the basins, where salt movement and volcanic build-ups created long and tortuous pathways down to the basin, strongly controlling the presence and geometry of sandstone bodies as well as their facies distribution.

Salt ridges and volcanoes were important topographic barriers to submarine sediment gravity flows. Such barriers not only deviated flows, and prevented their unconfinement, but also blocked flows, preventing the evolution of bipartite currents. As a major consequence, the stacking of apparently massive sandstones as thick as 800m located in one side of salt ridges, coexist with almost no sand at all, on the opposite flank of the very same salt ridge.

Volcanoes have also played an important role: earthquakes associated with volcanism locally triggered submarine sediment gravity flows instablizing previously deposited sand accumulations and accounted for the deposition of important reservoirs in the SE-Brazil offshore basins.

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