Seismic stratigraphic analysis of the Pre-salt of Berbigão, Sururu, and Atapu fields, Santos Basin, Brazil

Abstract

The Pre-salt section of Santos Basin, formed during the Lower Cretaceous, hosts one of the world's most significant hydrocarbon provinces, yet its complex carbonate reservoirs are yet to be fully understood. This study consists of a seismic analysis and interpretation of the Pre-salt interval of Berbigão, Sururu, and Atapu fields, focusing on the Upper Barra Velha Formation. A 3D seismic volume and sixteen wells were analyzed. At the Pre-salt level, five seismic units were defined. Distinct seismic facies were described and mapped throughout the Sag unit. These seismic facies were analyzed for occurrence patterns and incorporated with data from lithofacies and electrofacies. It was concluded that seismic facies Parallel corresponds to carbonate platforms principally composed of spherulitestone and mudstone variations and developed in both high- and low-energy sublittoral lake zones. Seismic facies Divergent Wedge and Fill represent profundal sediments deposited in deeper portions of the lake, where a higher concentration of organic-rich shales and mudstones would occur. This element is often associated with syndepositional faulting in the Sag unit. Seismic facies Mound represents carbonate mounds predominantly composed of shrubstone variations and shrubby spherulitestones. They occur along deep-seated faults and contain conspicuous amounts of silica and uranium. Mounds likely formed in intermediate to shallow sublittoral zones, being occasionally subjected to subaerial exposure. The formation and enrichment of these carbonate mounds are likely associated with hydrothermal processes, where faults would have acted as conduits for the percolation of hydrothermal fluids. Significant concentrations of shrubs in the Upper Barra Velha Formation are probably related to carbonate precipitation from hydrothermal fluids. The interpretations derived from this integrated study provide new insights into reservoir heterogeneity in the Upper Barra Velha, with direct implications for reservoir prediction, well placement, and production optimization in similar Pre-salt settings.