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Prospectivity of the Equatorial Conjugate Margins of Africa and South America

Wells, Steven; Greenhalgh, Jennifer C.; Borsato, Ron
Reservoir, Petroleum Geo-Services, Weybridge, United Kingdom.

The rifted passive margins of the Atlantic have been established as a world-class petroleum province. Although the South Atlantic has been a major focus of attention for conjugate margin exploration, recent interest has shifted north to the potential for undiscovered resources on the Equatorial Transform Margin, encompassing the offshore basins of Nigeria, Benin, Ghana, Cote d'Ivoire, Liberia and Sierra Leone on the African side and Guyana, Suriname, French Guiana and Northern Brazil on the American side. The Jubilee discovery offshore Ghana, made by Tullow in 2007, opened up a surplus of new and underexplored basins, and indicated the potential for further significant discoveries on the Equatorial margins.

The African side is currently the more developed of the two margins. Analysis of the regional geology in conjunction with the distribution of fields and discoveries reveals trends and can help characterise successful petroleum systems and play types. The best-known of the African fields is the Jubilee field in the Tano Basin offshore Ghana. Jubilee was discovered with the Mahogany-1 well in a series of turbidite fans and channels of Campanian to Turonian age, with excellent production characteristics, draping over a rifted high and pinching out up-dip. Similar success stories exist elsewhere on the margin.

Comparatively little production occurs on the South American margin despite a recent increase in activity. Almost no fields exist offshore and wells drilled are restricted to a narrow zone on the shelf break. However, with their Zaedyus discovery in 2010, Tullow and partners proved up the ‘Jubilee analogue' on the South American side of the conjugate margin. The Zaedyus well hit 72m of net pay in two turbidite fans in a similar play to Jubilee. A composite stratigraphy of the South American Equatorial basins shows many similarities to the African margins and indicates hydrocarbon potential at multiple stratigraphic levels in a predominantly post-Albian deep marine setting. Regional gravity and magnetic data along with modern seismic datasets over the South American margin also indicate a similar structural history and setting for these sub-basins to those on the African side. The key to successful exploration in this region, much like on the African margin, is a spatial balance between the provision of quality marine source rock and likelihood of reservoir sand input from the shelf, making regional paleogeographic reconstructions crucial..

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012