Abstract

Petroleum exploration along the West African and South American Equatorial Margin has led to important oil discoveries along both margins. Similar geochemical characteristics of these finds suggest analogous petroleum systems with enormous potential in the conjugate margin sedimentary basins. The Jubilee giant oil discovery offshore Ghana has an estimated recoverable reserve of about 600 million barrels. In the area that was once connected to the equatorial West African margin, but is now separated by the Atlantic Ocean, two discoveries have recently been announced. Tullow Oil announced the Zaedyus discovery offshore French Guinea, with 72m net oil pay in turbidite sandstones. Petrobras and BP announced the Pecem discovery in the northern Brazilian margin, with 140m of net pay in 2,129m water depth in the Ceará Basin. These discoveries appear to have a very similar geologic evolution, source rock facies, and oil types suggesting similar petroleum systems. Additionally, the integration of high resolution geochemical data from oils recovered from boreholes offshore the other basins along the South Atlantic Equatorial Margin has revealed four separate source rock systems: 1- an Aptian/Barremian calcareous black shale associated with a lacustrine brackish to saline anoxic environment; 2- a Late Aptian calcareous shale deposited in transitional environments, as indicated by oils found in the Ceará and Potiguar basins; 3- an Albian/Cenomanian/Turonian marine shale corresponding to an anoxic event widespread in the West African salt basins, particularly in the deep water settings of the Ghana and Angola continental margins. Similar oils have also been registered in the Foz do Amazonas Pará-Maranhão basins and in five ultra-deep water accumulations discovered recently (2011–2012) in the Sergipe Basin; 4- Paleocene-Eocene shales deposited in deltaic environments in the Niger Delta, the Amazon Cone, and Pará-Maranhão Basin. This work aims to restore these basins to their previous pre-breakup locations and to support new exploration efforts. Despite similarities shown above, simply matching discoveries in the conjugate margin basins, for example the Tano Basin offshore Ghana, with the Ceará Basin in northern Brazil, does not necessarily yield the entire story that may lead to a successful end. There is a great deal of contrasting sedimentary and structural development peculiarities from basin to basin and margin to margin. The application of a high-resolution petroleum system approach can lead to better exploration models for these basins and provide clues on the best strategy for drilling the new prospects that have been identified in the ultradeepwater regions of the South Atlantic Equatorial Margin.

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