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James M. Brooks1, Bernie B. Bernard1, Nick Cameron2, John Zumberge3, Mario G. P. Brandão4
(1) TDI-Brooks, College Station, TX
(2) TDI-Brooks
(3) GeoMark Research, Houston, TX
(4) Sonangol

Abstract: Surface geochemical exploration surveys identify active petroleum systems in deepwater Angola

Surface geochemical exploration (SGE) studies have located and quantified active petroleum systems operating within previously undrilled regions of the Angolan continental margin. Active oil generation and migration in Angola expresses itself visually as oil-staining within or throughout a core. In addition to the widespread macroseepage of oil, microseepage of oil and gas identified through geochemical analyses of the cores is also common. Three SGE studies have been performed offshore Angola in the deep water (1994 and 1996, approximately 700 cores) and ultradeep water regions (1997, approximately 470 cores). These studies high graded areas and prospects by defining areas of active oil migration and charge through routine gas and high molecular weight hydrocarbon screening methods. A comprehensive suite of analytical techniques were used on the cores to define the regional hydrocarbon seepage patterns within the study areas. On a secondary level, the SGE coring studies were used to define the distribution of oil sources, families, and maturities. This goal required accompanying oil and rock data for cross correlation with the seep data. The regional SGE programs on the Angolan margin utilized biological marker and isotope correlations of macroseep samples with regional oils. The macroseep and representative oil samples were both characterized using detailed molecular and isotopic analyses. The results of these studies show that there is significant and widespread macro- and micro-seepage of oil in deep and ultra deepwater regions offshore Angola. Migrant oil was predominantly of Post-Salt origin, but Pre-Salt oils were also identified.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana