Abstract: Libya: Petroleum Systems of the East Sirte Basin

BURWOOD, RALPH

Located within an extensive Mesozoic/Cenozoic basinal development, the Eastern Sirte Basin is a prolific oil province containing a number of super-giant fields including Amal, Augila-Nafoora, Messla and Sarir-C, for which cumulative reserves are in excess of 23 GBOR. Dominantly an oil habitat, production from reservoirs ranging in age from the Precambrian to Oligocene comprises high quality low sulphur content oils, often with a tendency towards high waxiness.

The NW-SE trending Agedabia Trough forms the main structural feature of the hydrocarbon habitat with the cognate Hameimat, Maragh and Sarir Troughs providing other important contiguous depositional centers. Whereas Paleogene subsidence has facilitated maturation and the generative process, Mesozoic basin fill sediments, notably the Late Cretaceous, provide source rocks for the functioning petroleum system(s).

Although the marine-deposited Senonian Sirte Shale Fm. (!) petroleum system is thought to dominate the habitat, application of geochemical inversion procedures to oil biomarker and stable isotope data attest to a greater diversity amongst these petroleums. Delineation of five end-member generic oil families implies an equal complexity in contributory petroleum systems, mixed-system aggregate oils also being evident. Application of procedures recognising the interplay of non-marine (lacustrine) source inputs clearly differentiate petroleums of such provenance. Systematic screening of a composite stratigraphic section has additionally identified source potential in Nubian (Triassic), Rachmat/Tagrifet (Late Cretaceous), Harash (Paleocene) and Eocene sediments.

Assignment of petroleum provenance has been achevied via multivariate oil data analysis and application of a carbon isotope - based source kerogen - oil correlation procedure. Four of the end-member petroleum systems have been unequivocally identified as the Sirte Shale Fm. (!), Nubian (Triassic), Harash Fm. (!) and Antelat Fm.(!) contributors. The remaining systems rely upon Pre-Upper Cretaceous lacustrine sediments specific to the Hameimat and Sarir Troughs.

Whereas numerous archetypal Sirte Shale Fm. (!) oils were recognized (e.g. Messla, Hamid, Sarir-L, etc), many of the major fields, including Areal, Augila-Nafoora, and Sarir-C, draw upon mixed system charging.

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

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria