Petroleum Geology of Eastern Brazilian Continental Margin

Abstract

Five petroleum provinces are known on the eastern Brazilian continental margin: Reconcavo, Sergipe-Alagoas, Espirito Santo, Potiguar, and Campos. Analysis of the petroleum habitat in these areas differentiates five petroleum reservoir systems: Late Jurassic, Neocomian, Aptian, Albian-Santonian, and Late Cretaceous-Tertiary. These systems are associated with five stages in the tectono-sedimentary evolution of the Brazilian coastal basins. 1. In the Late Jurassic petroleum reservoir system the reservoir rock is a fluvial blanket sandstone deposited during the prerift intracratonic stage. The petroleum migrated from Neocomian shales and was trapped by faulted blocks or unconformities on the crest of regional highs. The Agua Grande and Dom Joao fields in the Reconcavo basin, as well as the Caioba field in the offshore part of the Sergipe basin, are typical examples of this system. 2. The Neocomian petroleum reservoir system is associated with the deltaic-lacustrine depositional suite of the rift-valley stage. The oil is trapped in arched structures within regional depressions which have subsided along major fault trends. The Miranga and Aracas fields in the Reconcavo basin are the best examples. Minor stratigraphic fields such as Candeias in the Reconcavo basin also belong to this system. 3. The Aptian petroleum reservoir system is associated with the evaporitic stage. The petroleum was generated in euxinic shales and accumulated in conglomerates and sandstones. The traps are broad and gentle paleogeomorphic highs or structures contemporaneous with the evaporitic section. The Carmopolis and Riachuelo fields in the Sergipe-Alagoas basin are typical examples. 4. The Albian-Santonian petroleum reservoir system is associated with sandstones and carbonate rocks of the shallow-marine proto-oceanic stage. The oil accumulations are sealed in faulted blocks and paleogeomorphic traps. The Garoupa and Namorado fields in the Campos basin are examples. 5. The Late Cretaceous-Tertiary petroleum reservoir system is in turbidites of the open-oceanic stage. The oil fields are stratigraphic-trap type and the source rocks are continental-slope shales of the Calumbi Member and Urucutuca Formation. The Guaricema field in the offshore part of Sergipe basin and the Fazenda Cedro field in Espirito Santo basin are good examples of this system.