ABSTRACT: Petroleum Generation, Migration, and Accumulation in Deep-Water Area of Campos Basin, Brazil

L. A. F. Trindade, A. L. Soldan, J. R. Cerqueira, J. C. Ferreira, M. R. Mello, M. Carminatti, J. L. Dias

In recent years, several giant oil accumulations have been discovered in the offshore area of the Campos basin, southeast Brazil, in water depths up to 1500 m. Regional mapping of several sequences within Lagoa Feia Formation reveals thick source rock shales (more than 200 m), with excellent source potential, mature in most of the basin since the Coniacian. A close correlation between source rock depocenters and oil accumulations is present. Geochemical and biomarker data indicate source rock deposition in a lacustrine saline water environment. In deep water, petroleum is accumulated in turbiditic reservoirs ranging from Albian/Cenomanian to Miocene. The migration pathway model involves oil transport through windows in the Aptian salt layer reaching growth faults that act as conduits to turbiditic reservoirs. The oils were submitted to different degrees of biodegradation and there is evidence of mixed biodegraded and unaltered oils, suggesting more than one migration and biodegradation phase. First, the reservoirs were shallow at low temperatures and the oils were extensively biodegraded. Now, lighter fractions mixed with biodegraded oil are found far away from faults and in the highest positions of the reservoirs. Growth fault activity and migration events were tentatively correlated and can be used to explain different migration events charging the same reservoir.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990