A Compendium of Key Seismic and Geological Aspects for Characterizing the Upper Aptian Carbonate Reservoirs in the Brazilian Pre-Salt

Abstract

The Aptian carbonate reservoirs within the pre-salt section of the Santos Basin, such as the principal reservoirs of the Tupi Field, exhibit considerable heterogeneity in reservoir quality. This variability is influenced by several factors, including the widespread presence of magnesium clay minerals and diagenetic processes, which hampers hydrocarbon production. Given the lack of comprehensive reservoir-scale historical references, we revisit the reservoir zoning, inherent individualizations, facies distributions, seismostratigraphic, and tectonic features of the Barra Velha Formation within the Tupi Field. We spatially map key elements, decipher facies association profiles, and pinpoint porosity classes tied to facies and depositional or diagenetic characteristics from a multi-scale dataset comprising rock samples, well logs, and seismic data. A pragmatic seismostratigraphic zoning approach was employed to define intervals BVE100, BVE200, and BVE300 and their subzones. Reservoir quality was then linked with lake retraction periods, identified by an increase in well-developed shrubs displaying higher porosities and permeabilities, properties further amplified by dissolution phenomena. We also discuss the influence of structural positioning on facies distribution, associating higher carbonates with clay minerals proportions to structural lows, and reworked carbonates reservoirs to the structural highs and edges. We argue that only the BVE100 displays sag-type features, suggesting a mixed tectonic setting for BVE200. Furthermore, we characterized Feature X, a unique BVE100 high acoustic impedance signature associated with wells sampling elevated proportions of low-energy facies within structural flanks and lows. These insights carry significant implications for exploration and exploitation strategies in the studied area and can be applied to other pre-salt regions of any basin.