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Stretching a Point: Correlating Oil Family Signatures to Reunite Orphans with Their Families in a Trans-Atlantic Village of Basinsvillage of Basins

Dickson, William 1; Schiefelbein, Craig F.2; Odegard, Mark E.3
1 DIGs, Houston, TX.
2 Geochemical Solutions International (GSI), Houston, TX.
3 GrizGeo, Sugar Land, TX.

In petroleum systems work on the conjugate Atlantic margins of Brazil and West Africa, the authors have studied basins where geochemical data density offered better statistics but also where stubborn outliers required analysis and thought. This work considers some previously unique values - tight clusters or even single examples of oils from one lacustrine family: orphans. Geochemical re-analysis revealed possible matches; as confirmation, the correlations fit our basin reconstructions and so the orphans were reunited with their families.

Our methodology required four main steps. First, we re-classified a global sample set of 844 values into 6 oil families using multi-variate techniques (another paper in itself). Classified points were plotted on regional topographic and gravity maps (that define basins and sub-basins) as a spatial comparison of family assignments. For the South Atlantic passive margin basins, an additional test was reconstructing our data and interpretation using GIS-based software to move all points, lines and images to their respective paleo-locations as defined by a plate model from Chris Scotese et al. Examining relationships revealed by the oils and basin outlines followed two questions: Do points correlate by basin or sub-basin? Do inferred paleo-geologies fit the basins?

Singular examples included oils in the Malongo sub-basin, offshore Cabinda; and others up and down the Atlantic coast of Argentina and Brazil. Beyond finding families, these correlations improved our picture of the distribution and shapes of lacustrine basins along the conjugate margins and the likely hydrocarbon sourcing they could provide. One key insight in the Santos-Campos-Espírito Santo basins of Brazil was the establishment of a basin-wide pre-salt source (Dickson et al., 2005). These results will assist our next step, to consider source risks in areas that lack drilling or have no discoveries from lacustrine (pre-salt) source intervals.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009