CORNFORD, CHRIS, CHRIS BURGESS and RANALD KELLY, Integrated Geochemical Interpretation Ltd, Hallsannery, Bideford, Devon EX39 5HE, UK

Abstract: Modelling the Deep Water West African Margin - Transitional Crust, Transform Margins and Transient Heat Flow

Thermal geohistory and fluid flow modelling has been undertaken along the offshore basins of the western African margin from Cape Town to Casablanca. Corrected down hole temperature and a range of often conflicting maturity parameters were used to constrain the heat flow and generation histories of the various areas. Hydrocarbon occurrences are the only effective calibrant for fluid flow modelling. This super-basinal study illustrates a number of common features. In terms of the more conventional margins, convex burial histories and late generation are associated with sedimentary progradations over oceanic crust (Tertiary deltas), while concave burial histories and early generation are the norm on starved margins. Massive slope wasting events (slumping) occur repeatedly along the margin and provide a special case for 2-D modelling. Such 'tectonic' burial can prove vital for the timing of generation and pressure generation in delta front prospects.As expected, evidence for an elevated palaeo-heat flow event is found in transitional (continental/oceanic) crust, a feature surprisingly repeated along the Ivory Coast - Ghana transform margin. In both cases this leads to commercially unattractive early generation from syn-rift source rocks. Recognising these features on the mega-metre scale helps place limits on the risk associated with acquiring and relinquishing exploration acreage in this frontier area.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England