Abstract: Major Types of Deep-Water Reservoirs from the Eastern Brazilian Rift and Passive Margin Basins

Bruhn, Carlos H. L. - Petrobras/E&P

Turbidites and associated deep-water facies comprise the most important petroleum reservoirs in Brazil. They contain original in place volumes of 57.2 billion bbl of oil, and 27.5 trillion ft³ of gas, and total reserves of 12.5 billion bbl of oil, and 8.3 trillion ft³ of gas. Brazilian petroleum-bearing turbidites occur in (1) Carboniferous/ Permian, glaciomarine pre-rift (interior cratonic) successions, (2) Neocomian to Aptian, lacustrine rift successions, and (3) Upper Albian to Lower Miocene, marine passive margin successions. Most of the petroleum accumulations are distributed along the eastern Brazilian margin, which tectonic and sedimentary evolution is linked to the Neocomian breakup of Gondwana and the subsequent opening of the South Atlantic Ocean ( 1). Turbidites comprise 553 production zones from 171 oil and/or gas fields, mostly concentrated in the Campos, Reconcavo, Sergipe/Alagoas, and Espirito Santo basins. This paper presents an overview of the major types of Brazilian deep-water reservoirs, which general geological setting is indicated in figure 1.

The major types of Brazilian deep-water reservoirs are: (1) Gravel/sand-rich, turbidite channel complexes: 10-50 m-thick, 200-2,000 m-wide, and 0.5->10 km-long channel-fills, which can be clustered into 20-100 m-thick, 1-6 km-wide, and 1->10 km-long channel complexes. Type 1 reservoirs typically fill submarine canyons incised into the shelf or slope, or fault-bounded troughs in lacustrine rifts. (2) Trough-confined, gravel/sand-rich turbidite lobes: 10-140 m-thick, 1-12 km-wide, and 3->20 km-long tabular/lobate reservoirs confined to intra-slope troughs bounded by listric faults soling out on underlying evaporites. (3) Unconfined, sand-rich turbidite lobes: 5-60 m-thick, 2-8 km-wide, and 5-12 km-long lobes filling wide depressions developed by downslope gliding of underlying evaporites. Some lobes can be dissected by low- to high-sinuosity, 5-15 m-deep, 200-600 m-wide channels. (4) Sand/mud-rich turbidite lobes: 2-20 m-thick, 1-20 km-wide, and 2->20 km-long lobes, which are composed of turbidite sandstones and frequently interbedded background mudstones and debris flow deposits. They occur in similar settings as those for type 3 reservoirs, or are associated to deltaic systems from lacustrine rifts. (5) Gravel/sand-rich aprons: up to 2 km-thick, 5-20 km-wide, and 5-200 km-long wedges deposited by high-density turbidity currents and debris flows along border fault margins of lacustrine rifts. (6) Sand-rich, lacustrine density underflow deposits: up to 50 m-thick, 600-1,200 m-wide, and 1.5-4.5 km-long sandbodies, which are confined to narrow (< 5 km), fault-bounded troughs subparallel to border fault margins of lacustrine rifts. (7) Sand/mud-rich debris flow deposits: Mounded to channelized, up to 400 m-thick, 200-4,000 m-wide, and 0.8-5 km-long muddy sandstone bodies, which are deposited by debris flows derived from the slumping of deltaic systems prograding into deep, lacustrine rifts. (8) Sandy bottom current deposits: Mounds (up to 40 m-thick) of interbedded mudstones and thin-bedded sandstones, typically overlying type 3 reservoirs.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil