Libyan Paleozoic: A Review of the Factors Limiting Hydrocarbon Potential

William H. Kanes, Alan E. M. Nairn, R. M. Aburawi

Of the three main Paleozoic basins--Ghadames, Murzuq, and Kufra--only the Ghadames and its continuation into Algeria, the Illizi (or Fort Polignac) basin, has yielded hydrocarbons in significant quantity. The Paleozoic on the Cyrenaica platform and "basement" of the Sirte basin has a potential not fully considered. The paleogeography of the Paleozoic system is reviewed to illustrate the extent to which inherited and reactivated basement-controlled structures have influenced later Paleozoic sedimentation and hence the distribution of source rocks, reservoirs, and seals.

In all instances, the source rocks are restricted to shales of the Tanezufft Formation or occur in the Upper Devonian Aouinet Oeunine Formation. Multiple fine-grained sequences serve as seals in all the fields. The reservoirs range from the well-cemented but highly fractured Cambrian-Ordovician Gargaf sandstones to the Acacus-Tadrart clastics to the fine-grained Lower Carboniferous Tahara Sandstone. The principal plays are associated with minor structures, and stratigraphic trapping mechanisms play a minor role. The average field size (excluding the Sirte basin) is approximately 80 million bbl of recoverable oil.

Paleozoic structural plays in the Sirte basin and the Cyrenaica platform include reactivated infra-Cambrian faults. The lower Paleozoic accumulations of the Murzuq basin are tied to large structures.

With the exception of local areas in the Ghadames basin, the Paleozoic succession remains a stratigraphic frontier province--still incompletely explored but with several interesting possibilities for large amounts of stratigraphically trapped hydrocarbons.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.