--> Abstract: Petroleum System Concepts Applied to Sirte Basin (Libya) Exploration, by R. Burwood and J. Redfern; #90923 (1999)

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BURWOOD, RALPH, Fina Exploration Ltd, Epsom, and JONATHAN REDFERN, Oxford Brookes University, Oxford, UK

Abstract: Petroleum System Concepts Applied to Sirte Basin (Libya) Exploration

The Eastern Sirte Basin is a prolific Mesozoic/Cenozoic oil province containing a number of super-giant fields including Amal,Augila-Nafoora, Messla and Sarir-C, cumulative reserves being in excess of 23 GBOR. Production from reservoirs ranging in age from the Pre-Cambrian to Oligocene is of premium quality, low sulphur and often highly waxy oils.

Although the Agedabia Trough forms the main structural feature of the hydrocarbon habitat, the older Hameimat, Maragh and Sarir Troughs provide other important prospective depositional centres.Whereas Paleogene subsidence has facilitated the generative process, Mesozoic basin fill sediments, notably the Early and Late Cretaceous, provide source rocks for the productive petroleum system(s).

Conventionally, the marine-deposited Senonian Sirte Shale Fm. source system was thought to provide the dominant charge. However, application of geochemical inversion procedures to biomarker and isotope data attest to a greater diversity amongst these oils. Delineation of seven end member generic oil families implies an equal complexity in contributory petroleum systems, mixed system hybrid oils also being evident. Application of procedures recognising the contribution of nonmarine (lacustrine) source inputs clearly differentiate petroleums of such provenance. Systematic screening of a composite stratigraphic section has additionally identified source potential in Nubian (Triassic and Early Cretaceous), Rachmat/Tagrifet (Late Cretaceous), Harash (Paleocene) and Eocene sediments.

Assignment of petroleum provenance has been achieved via multivariate oil data analysis and application of a carbon isotope-based source kerogen-oil correlation procedure. Major end-member petroleum systems have been definitively identified as the Sirte Shale Fm.(!), Rachmat/Tagrifet Fins (!), and Nubian (Triassic) contributors. The remaining systems rely upon Pre-upper Cretaceous lacustrine sediments specific to the Hameimat and Sarir Troughs plus Harash Fm. (!) and Antelat Fm.(!) curiosities.

Whereas numerous archetypal Sirte Shale Fm. (!) oils were recognised (e.g. Messla, Hamid, Sarir-L etc), reserves for many of the major fields, including Amal,Augila-Nafoora, and Sarir-C rely on hybrid system charging.

These results confirm that the prospectivity of the Sirte Basin is not exclusively dependent upon the Sirte Shale Fm. (!) with other, often hybrid, petroleum systems in operation.

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