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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.

The Eocene deep-water sand-rich deposits of the Grès d’Annot of southern France have been used as outcrop analogues for offshore Cretaceous reservoirs of Campos Basin, southeastern Brazil. The analogy is chiefly based on the sand-rich, confined nature of the two systems. Such application can be questioned as the contrasting geological settings, i.e. convergent versus passive margin, could produce rather different depositional scenarios. Detailed comparison between the two systems permits, however, recognizing additional similarities, and also some differences, whose recognition is important to ensure the correct application of the Grès d’Annot as an analogue for this and other passive-margin reservoirs. Comparative analysis of channel dimensions, facies continuity, and three-dimensional expression suggests that confined sand-rich systems show many similarities in terms of critical reservoir heterogeneity, providing that palaeotopographic control was similar, regardless of the tectonic environment in which they were formed. In addition, contrasts found among sequences in the same tectonic setting suggest that other factors (such as, for example, sand/shale ratio of the sediment input) play an important role in defining reservoir architecture. These observations further suggest that, once similarities and differences are correctly understood, analogue data, even from quite different tectonic settings, may provide a powerful tool for improving subsurface reservoir models.

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