Chapter 1
Petroleum Systems of South Atlantic Marginal Basins--An Overview

B. J. Katz
Texaco Group Inc.
Houston, Texas, U.S.A.

M. R. Mello
Petrobrs Research Center
Rio de Janeiro, Brazil

ABSTRACT

The marginal basins along the South Atlantic have developed into one of the most active regions for petroleum exploration. The increase in the level of industry interest has resulted from numerous recent successes along both the eastern and western continental margins of the South Atlantic, the evolution of the region's political character, and an increase in the rate of permitting in deep and ultradeep waters. This heightened industry interest provided the rationale for a Hedberg Research Symposium on the petroleum systems of South Atlantic marginal basins.

Use of the petroleum system concept in South Atlantic marginal basins provides an effective means of classifying and characterizing the diversity of the systems and a way to aid in the selection of appropriate exploration analogs. South Atlantic marginal basins provide some of the best examples of how petroleum systems evolve through time with respect to both their levels of certainty and their areal and stratigraphic limits. A comparison of three basins from the South Atlantic--the Niger Delta, Lower Congo, and Campos Basins--provide examples of both the common traits that exist throughout the region as well as the differences among the individual basins. Differences are clear when the source and reservoir couplets are examined. In the Niger Delta, shallow water sands are charged from a Tertiary source with an important higher plant contribution. In the Lower Congo Basin, the lacustrine Bucomazi Formation (Neocomian-Barremian) charges primarily shelfal carbonates and sandstones. In the Campos Basin, the lacustrine Lagoa Feia (Barremian) Formation charges primarily Upper Cretaceous-Tertiary deep-water turbidite sandstones. A common trait appears to be the nature of the migration network which typically incorporates both normal faults and regional unconformities. The relative importance of vertical and lateral migration does differ among the basins, with vertical migration and short-distance lateral migration being dominant in the Campos and Gabon Basins and longer lateral distance migration being more important in the Niger Delta.

The basins of the South Atlantic also provide an excellent opportunity to examine the variety of lacustrine source rock settings. The depositional settings of these lakes range from freshwater to hypersaline. Source quality within these units also varies in response to their different depositional conditions and other factors that control or influence organic productivity and preservation.