Chapter 2
Geochemical Comparison of Crude Oil Along the South Atlantic Margins

C. F. Schiefelbein
GeoMark Research, Inc.
Houston, Texas, U.S.A.

J. E. Zumberge
GeoMark Research, Inc.
Houston, Texas, U.S.A.

N. C. Cameron
GeoMark Research, Inc.
Houston, Texas, U.S.A.

S. W. Brown
GeoMark Research, Inc.
Houston, Texas, U.S.A.

ABSTRACT

The continental margin basins of Brazil and west Africa share very similar tectonostratigraphic units because of their proximity in Late Jurassic-Early Cretaceous time. As a result of the paleogeographic ties between the South American and the African plates, the oil habitat of the marginal basins of both continents can often be correlated. To better understand the petroleum systems along the South Atlantic margins, geochemical results obtained from the analysis of 290 oils from the major Brazilian and west African coastal basins were statistically evaluated to establish genetic relationships, distinguish source paleoenvironments and age, and identify different petroleum systems. A number of general oil families composed of genetically related oils were identified, several of which contain oils from both sides of the margin. Areas where oils of mixed provenance occur are also identified.

Presalt (Neocomian-Aptian) lacustrine oils can be separated into at least three distinct families and are present in the Congo, Lower Congo, and Benguela Basins of west Africa and the Recncavo, Campos, Potiguar, Cear, and Bahia Sul Basins of Brazil. Genetically related oils may be present in the Campos Basin and offshore central Angola and in the Recncavo Basin and central Gabon and northern Angola.

Postsalt (Upper Cretaceous-Tertiary) marine oils are present in the Ivory Coast and the northern Gabon, Lower Congo, Kwanza, and Benguela Basins of west Africa and the Santos, Esprito Santo, and Sergipe-Alagoas Basins of Brazil. Oil mixing may have occurred in the Ivory Coast, Lower Congo, and Kwanza. Genetically related oils may occur in the Sergipe-Alagoas Basin and from northern Gabon. Oils from Nigeria, Benin, Equatorial Guinea, Cameroon, offshore northern Angola, and the Foz do Amazonas Basin of northern Brazil originated from Tertiary source rocks primarily composed of terrigenous organic matter deposited in fluvial deltaic or nearshore marine environments.