The Upper Cretaceous Sedimentary Succession in Brazilian Equatorial Margin - A Stratigraphic-Trap Prone Succession for Hydrocarbon

Pessoa Neto, Otaviano D.¹; Figueiredo, Jorge P.¹
(1) Exploration, PETROBRAS S.A., Rio de Janeiro, Brazil.

The Brazilian Equatorial Margin (BEM) extends for more than 2000 km and comprises five offshore basins (from SE to NW: Potiguar, Ceará, Barreirinhas, Pará-Maranhão and Foz do Amazonas). The continental breakup that eventually separated South America from Africa and that originated the Equatorial Atlantic Ocean evolved diachronically over the Albian, from SE to NW. The entire Upper Cretaceous sedimentary succession in offshore BEM is a typical drift sedimentary infill, roughly correlated over the whole margin. Two major Upper Cretaceous depositional successions are identified. The lower succession (Albian to Campanian) has an overall transgressive character and is dominated by fine-grained siliciclastic sediments in the proximal portion of the basin, which has been sampled by wells drilled over the last forty years; however, carbonates are also present in some basins. The upper succession (Campanian-Maastrichtian) has an overall regressive character and is rich in coarse-grained siliciclastic sediments in the proximal regions of the basins, with minor carbonate sedimentation. This scenario suggests a perfect situation for the establishment of a Petroleum System in deep waters of the entire BEM. The lower transgressive succession comprises at least two intervals deposited during oceanic anoxic events (OAE1d and OAE2). These intervals correspond to potential source rocks in deep waters. On the other hand, the upper regressive succession contains the sandy deposits required for reservoir in the deep basin, brought via gravitational flows. Overlying the Upper Cretaceous succession, the Tertiary deep water sedimentary succession provided the load for petroleum generation; the regional seal and the thin-skinned tectonism that can work in order to facilitate oil migration or help entrapment by forming distensional and compressional structures. This first order optimum scenario interpreted from regional 2D seismic data is punctuated by higher order events that have been identified in more recent high resolution 3D seismic data acquired in deep waters. The new data have revealed that the whole Upper Cretaceous deep water succession is prone in unstructured deposits (channel complex sets fills and lobes), which are potential stratigraphic traps for hydrocarbon similarly to the recent giant oil discoveries in the African Equatorial Margin.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.