--> Abstract: High-Resolution Sequence Stratigraphy and Reservoir Characterization of Oligocene/Miocene Sand-Rich Turbidites from Deep-Water Campos Basin, Brazil, by C. H. L. Bruhn, L. M. Arienti, D. D. Castro, T. Adams, A. P. Barros, D. J. Sarzenski, and Z. Camoleze; #90933 (1998).

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Abstract: High-Resolution Sequence Stratigraphy and Reservoir Characterization of Oligocene/Miocene Sand-Rich Turbidites from Deep-Water Campos Basin, Brazil

Bruhn, C. H. L.; L. M. Arienti, D. D. Castro, T. Adams, A. P. Barros, D. J. Sarzenski, and Z. Camoleze - Petrobras/E&P

This paper presents the high-resolution sequence stratigraphic framework, sandbody geometry, and reservoir heterogeneities of Oligocene/Miocene sand-rich turbidites, which comprise a giant oil field in deep water (300-800 m) Campos Basin, Brazil. The studied turbidites form part of a Middle Eocene to recent regressive succession, which displays a mostly offlapping, progradational pattern throughout the eastern Brazilian margin.

The reservoir is composed of the amalgamation of sand-rich, 56 channel-fills and 12 lobes. Individual channel-fills are up to 40 m-thick, 500-2,000 m-wide, 2->10 km-long, and show moderate to low sinuosity. Channel-fill facies comprise: (1) unstratified, 0.5-2.0 m-thick, normally-graded beds of intraformational (carbonate and mud-intraclasts) conglomerates, intraclastic sandstones, and very coarse- to medium-grained sandstones; (2) unstratified, medium- to fine-grained sandstones with a few, dispersed cobble- to granule-sized mud intraclasts; and (3) interbedded mudstones and thin-bedded (< 0.5 m) fine- to very fine-grained Tab, Tabc, and Tbc Bouma beds. Channel-fills truncate or can be laterally associated to non-reservoir, levee deposits composed of interbedded mudstones and thin-bedded (< 0.3 m), very fine-grained, rippled sandstones. Individual channel fills are clustered into 6 channel complexes (up to 100 m-thick, 1-6 km-wide, and 3->10 km-long; Fig. 1), which can be discriminated on the basis of (1) bounding unconformities, (2) thicker, interbedded levee successions, (3) interbedded marker beds, (4) different filling facies, and (5) changes in channel orientation. They are named CC3, CC4, CC5, CC6, CC7, and CC10 (from the oldest to the youngest; Figs. 1, 2). Lobe deposits are composed of (1) unstratified, very coarse- to fine-grained sandstones, and (2) medium- to very fine-grained, Tab, Tabc, and Tbc Bouma beds. They comprise up to 30 m-thick, 2-6 km-wide, and 2->10 km-long sandbodies, grouped into 4 lobe complexes (L1-L2, and L8-L9; Figs. 1, 2). Both channel-fill and lobe facies are poorly-consolidated, poorly-sorted, and have low silt (<10%) and clay (<2%) contents. Average porosities and permeabilities are essentially a function of grain size and sorting, varying between 20% and 550 mD (intraclastic conglomerates), and 31 % and 1060 mD (very fine-grained sandstones).

Despite the uncertainties involved, we suggest that at least one of the lowermost unconformities recognized in the study section (basal boundaries of CC3 and CC4; Fig. 1) can be correlated to an eustatic, third-order sea-level fall of about 25 Ma. Eight of studied turbidite successions (CC3 to CC10) are included in a calcareous nannofossil zone spanning only 1.8 m.y. (25.2-23.4 Ma; Fig. 1), having an average duration of 225,000 yr. Therefore, the unconformity-bounded channel complexes CC3 to CC7, and CC 10 probably comprise 4th-order sequences.

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