Ralph Burwood¹, Michael Cope¹, Jonathan Redfern¹
(1) Oxford Brookes University, Guildford, United Kingdom

Abstract: Petroleum system concepts applied to Sirte Basin (Libya) Exploration

With cumulative reserves exceding 23 GBOR, the Eastern Sirte Basin is a prolific oil province hosting super-giants such as the Amal, Augila-Nafoora and Sarir fields. Production from Pre-Cambrian to Oligocene-age reservoirs is of low sulphur and often highly waxy oils.

The Late Mesozoic/Cenozoic Agedabia and older Hameimat, Maragh and Sarir troughs provide the main structural features of the habitat and control hydrocarbon prospectivity. Paleogene subsidence has facilitated the generative process with Mesozoic basin fill sediments hosting source rocks for productive petroleum system(s). Traditionally the marine Senonian Sirte Shale Fm. source was thought to provide the dominant charge. Application of geochemical inversion procedures to oil data, however, attest to a greater diversity. Delineation of seven end-member generic oil families implies an equal complexity in contributory petroleum systems, mixed-system hybrid oils also being evident. Non-marine (lacustrine) source inputs are also in evidence differentiating 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 oil provenance has been achieved via multivariate oil data analysis and application of a carbon isotope-based source kerogen-oil correlation procedure. End-member petroleum systems have been definitively identified as the Sirte Shale Fm.(!), Rachmat/Tagrifet Fms (!), and Nubian (Triassic) contributors. The remaining major systems rely upon Pre-upper Cretaceous lacustrine sediments specific to the Hameimat and Sarir Troughs. Whereas numerous archetypal Sirte Shale Fm. (!) oils were recognised (e.g. Messla, Hamid, Sarir-L etc), reserves for many of the giant 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 #90914©2000 AAPG Annual Convention, New Orleans, Louisiana