Structurally Controlled Sand-Rich Gravity Deposits of the Jubarte Oil Field (BRazil Deep Seds - Deep-Water Sedimentation on the Southeast Brazilian Margin Project)

R. C. Gontijo¹, C. E. Souza Cruz¹, J. L. L. Caldas², L. M. Arienti¹, and R. S. F. D'Avila^1
1 Petrobras, Rio de Janeiro, Brazil
² Petrobras, Vitoria, Brazil

The Jubarte oil field, about three billion barrels oil in place, is located in the Northern Campos Basin, in water depths ranging around 1250m.

Deep troughs created by salt-rooted growth faults were the preferential pathways for the Maastrichtian sediment-rich gravity flows. The Jubarte trough, 8 to 14km long and 1.5 to 5.5km wide, was filled in by coarse-grained sediments deposited by highly confined density flows. The main reservoirs are constituted by several amalgamated small channels (150-300m wide, 30-50m deep) comprising a channel belt ranging from 600m to 1km wide.

The main sedimentary facies observed both in cores and image logging are conglomerates, massive and cross-bedded sandstones, marls, and chaotic debris flows. The depositional cycles are metric thick, fining-upward, composed of conglomerates, coarse-grained sandstones, aligned pebbles, and fine-to-medium sandstones. The amount of pebbles and granules inside the cycles varies according to the flow velocity.

Grains are predominantly angular to sub-angular composed of quartz, feldspars, lithics, and coal and vegetables fragments, strongly suggesting erosion of nearby continental areas during major fluvial floods, which would have triggered sediment-rich hyperpicnal flows. In their proximal area, the fault-generated troughs evolved to steep submarine canyons, which probably captured the hyperpicnal flows and acted as a by-passing zone, driving the sediments directly to a deeper water marine setting, where the elongated and tortuous space between adjacent salt ridges controlled the depositional space of the oil-rich sandstones.

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