Petroleum Systems Asymmetry Across the South Atlantic Equatorial Margins
Published:December 01, 2015
William Dickson, Craig Schiefelbein, Mark Odegard, John Zumberge, 2015. "Petroleum Systems Asymmetry Across the South Atlantic Equatorial Margins", Petroleum Systems in “Rift” Basins, Paul J. Post, James Coleman, Jr., Norman C. Rosen, David E. Brown, Tina Roberts-Ashby, Peter Kahn, Mark Rowan
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Our petroleum systems interpretation followed two lines of evidence, considering both tectonic-structural evolution and hydrocarbon geochemistry. Our structural mapping was based on compilations of geophysical data and a review of both published literature and oil company public presentations. Geochemically, we accessed regional nonexclusive oils studies of the conjugate margins of Africa and South America, plus considerable published material.
The nonexclusive oils data was refined, with multiple passes, to a group of 286 oils, of which 48 were key to our understanding of the West African Transform (WAT) Margin. Although multiple lacustrine-sourced oil families are seen around the South Atlantic margins, a rich, oil-prone lacustrine source would be a surprise offshore Ivory Coast and Ghana. There is minor evidence of mixed source, possibly lacustrine stringers within an alluvial to marine setting, but the predominant source is marine Cretaceous (Cenomanian–Turonian and possibly Albian).
Opening asymmetry of the Equatorial Margin (A) biased the location of lacustrine (early to mid-Cretaceous prerift to early synrift) source rocks to the northeast Brazil margin and (B) locally narrowed the width of the optimal marine (well known mid to Late Cretaceous postrift) WAT margin source kitchens. Burial of the latter, offshore Ivory Coast and Ghana, aggravated the risk of late charge of light (condensate and gas) hydrocarbons.