Bottom-current reworked Palaeocene–Eocene deep-water reservoirs of the Campos Basin, Brazil
Marco A. S. Moraes, Walter B. Maciel, Mario Sérgio S. Braga, Adriano R. Viana, 2007. "Bottom-current reworked Palaeocene–Eocene deep-water reservoirs of the Campos Basin, Brazil", Economic and Palaeoceanographic Significance of Contourite Deposits, A. R. Viana, M. Rebesco
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Deep-water reservoirs consisting of turbiditic sandstones moderately to heavily reworked by bottom currents are common in canyon- and trough-filling deep-water (bathyal) Palaeocene-Eocene sequences of the Campos Basin, offshore southeastern Brazil. A number of wells with conventional logs, together with cores, provided the database for the study. Seismic data provide additional support, but low resolution and noise hamper detailed analysis. The sandstones presenting better reservoir quality in these sequences are interpreted as being deposited by turbidity currents, as suggested by the dominance of unstratified normally graded sandstones, with grain sizes ranging from fine to coarse sand, and low clay-matrix content. Sandstones interpreted as bottom-current deposits (mid-water contourites) form poor-quality reservoirs, or baffles and barriers. These rocks are commonly moderately to heavily bioturbated, with variable, frequently high, clay-matrix content. Common trace fossils include Planolites, Palaeophycus and Zoophycos. Locally, these sandstones show faint horizontal stratification and planar cross-stratification. Contourites with thickness ranging from a few decimetres to several metres occur intercalated with turbiditic sandstones. Because they present distinct reservoir qualities, the mapping of the limits between turbidites and contourites is critical for adequate reservoir characterization. Most of this mapping has been performed using well information, constrained by outcrop analogues. The currents responsible for reworking turbiditic sands are interpreted to be deviated geostrophic currents, with velocity enhanced in narrow canyons and troughs.