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Stratigraphic Analysis and Facies Distribution Model in the Aptian of Campos Basin, Brazil

Moises C. Muniz, Previous HitFlavioTop Roberto B. Oliveira, Carlos E. Souza Cruz, and Nilo S. Matsuda
E&P, PETROBRAS, Rio de Janeiro, Brazil

One of the most exciting challenges in the study of South Atlantic Passive Margin Basins is the analysis of Aptian sedimentological and stratigraphic frameworks, which composes the transitional phase of the South Atlantic opening. These rock frameworks overlies the Pangea break up unconformity in the Early Aptian, above syn-rift Barremian continental section and underlies a thick layer of the Late Aptian evaporites. In Campos Basin, they are characterized by a sag basin with about 300m thick sedimentary rocks. The genetic facies distribution normally shows clastic alluvial fans close to shoreline and shallow water carbonates basinward.

An evolutive model for the formation of Aptian rocks mainly in southern Campos Basin has been proposed based on the integration of 3D seismic interpretation, well logs, petrographic and stable isotopes data obtained by several wells drilled from nearshore to offshore.

Sedimentological and stratigraphic analysis show shallowing up stacking pattern in a transgressive context. Three mid term depositional sequences were defined within the lower to middle Aptian section. The cycles begin with sub-tidal facies association and culminate with subtidal to intertidal facies. Occasionally supratidal features such as breccias are observed; however they are more common nearshore or upon depositional heights. High energy facies are associated with sub-tidal sites at the zone of ancient wave break, close to the platform edge, and occur frequently at the top of stratigraphic sequence.

All these rocks represent deposits of very shallow and restrict environments, which are characteristic of transition from continental to marine system in Campos Basin. Geometry and facies distribution are strongly controlled by the paleogeography, so the tectonic control on deposition of these sediments establishes a role for the depositional facies prediction

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