Shaken, Not Stirred: Oil Family Cocktails in Brazil Margin Basins, with and Without Salt
There are many recipes but any good cocktail is made from elements in precise ratios, carefully
measured, mixed via stirring or shaking, and poured through a strainer into a prepared container of correct temperature. In studying the petroleum systems of Brazil’s margin, we recognize the same requirements.
The keys are:
1) ingredients: preserved organic matter deposited in lacustrine (both high and low salt), marine and rarely, terrestrial environments.
2) temperature: hot enough to generate hydrocarbons, varying with source type (Santos Basin pre-salt lacustrine Guaratiba vs post-salt marine Itajaí-Açu).
3) shaking (mixing): tilting due to basin subsidence and salt mobilization during percolation of geo-fluids (Campos Basin, especially Roncador field). The interplay of oceanic features (transform trend extensions, volcanic punctuations) is important in Espírito Santo and Sergipe-Alagoas basins.
4) the strainer: salt windows present (Santos Basin), absent or sometimes both, impeding or permitting migration; and salt diapirism sometimes puncturing top seals (outer Campos basin).
5) the container: cold enough to allow biodegradation (Roncador field) or warm enough to inhibit it.
We illustrate each of these points with examples along the margin from southern Santos to northern Sergipe-Alagoas basins and speculate on the applicability to basin neighbours.