Characteristics
The Sirte Basin ranks 13th among the world’s petroleum provinces, having proven oil reserves estimated at 43.1 billion barrels (6.85×109 m3) of oil equivalent (36.7 bbl, 37.7×1012 cu ft (1,070 km3) of gas, 0.1 bbl (0.016 m3) of NGL), an amount that constitutes 1.7% of the world’s known oil reserves. The basin consists of one dominant total petroleum system, known as the Sirte-Zelten.
The Late Cretaceous Sirte Shale is the primary hydrocarbon source bed. Reservoirs range in rock type and age from fractured Precambrian basement, clastic reservoirs in the Cambrian-Ordovician Gargaf sandstones, and Lower Cretaceous Nubian Sandstone to Paleocene Zelten Formation and Eocene carbonates usually in the form of bioherms.
Hydrocarbon generation commenced about 50 million years ago (Ma) in the deeper basins, about 40 Ma in many other areas, and may continue to the present day. Geothermal gradients generally range from 1 °F/100 ft to 1.8 °F/100 ft; horsts and grabens generally have roughly equivalent thermal regimes relative to the primary source rock. Along the southwest and west margins of the province are extrusive igneous deposits that tend to diminish the hydrocarbon potential of these areas. The Gialo High is a relatively small horst block in the eastern Sirte Basin. It is most important and primarily known for the stacked oil fields in rocks ranging from the Early Cretaceous to Oligocene age. There are several billion barrels of oil reserves associated with the structure both over the crest of the horst as well as flanking the high in the adjacent graben.
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