Petroleum Potential of the Libyan Sedimentary Basins

O. S. Hammuda, A. M. Sbeta

Contrary to prevailing opinion, all Libyan sedimentary basins and the Al-Jabal Al-Akhdar platform contain prolific petroleum accumulations with very high prospectivity. A systematic review of the types of traps and pays in this central part of the southern Mediterranean province reveals great variability in reservoir and source rock characteristics. The reservoir rocks are of almost all geologic ages, including fractured orthoquartzites of the Cambrian-Ordovician Al Hofra Formation; sand wedges of the Ordovician Memoniat Formation; clean sand stringers of the Silurian Acacus Formation; thin sand lenses and tongues of the Devonian Tadrart Sandstone; clean sands of the Carboniferous Tahara Formation; clastics and carbonates of the Triassic Kurrush and Al-Aziziyah Formation; Jurassic clastics of Al-Jabal Al-Akhdar and sandstones of the Abu Shaybah Formation; Lower Cretaceous clastics of the As Sarir Group and dolomites of Al-Alamin; Upper Cretaceous and Paleocene carbonate complexes, dolomites, reefal buildups, and bioherms (rudistid, coral, algal, and bryozoan); Eocene nummulitic and shell banks; and Oligocene regressive sandstones.

The thick source rock sequences also vary in nature and organic content. They include basinal graptolitic shales of the Silurian Tanezzuft Formation in the Ghadames, Murzuk, and Al-Kufrah basins; Devonian deltaic clastics of the Wan Kasa and Aouinat Aouinine Formations in the Ghadames and Murzuk basins; Triassic clastics and carbonates of the Kurrush (Ras Hamia) and Al-Aziziyah Formations; basinal organic Cretaceous shales of Ras Al-Hilal; Cretaceous and Paleocene organic shales of the Sirt and Hayfa Formations and Paleocene organic shales of the Al-Jurf Formation in the Gabes-Tarabulus basin; and organic matter of the sabkha evaporites of the Triassic-Jurassic Bir Al-Ghanam Group and the Lower Cretaceous Etal evaporites. The lower Eocene Gir Group should be considered as source rocks

These organic-rich facies have accumulated in intracratonic and passive margin basins or in marginal seas. Most of the oil discovered thus far in these basins is found in large structural traps. Future discoveries of stratigraphic traps or small structural traps will require intensified efforts and detailed studies using up-to-date multidisciplinary techniques in sedimentary tectonics, biostratigraphic facies analysis, and geochemical prospecting in order to develop a better understanding of these basins, thus improving their prospectivity.

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