Tectonic Sedimentary Evolution and Hydrocarbon Accumulation in Sirte Basin

Sirte basin has a huge oil-gas reserve. The analysis between tectonic-sedimentary evolution and oil-gas accumulation in this basin has a guiding role in search for similar hydrocarbon-rich basins. According to IHS database, the tectonic evolution of Sirte basin can be divided into four ages: (1) Early riftting age: The Precambrian Pan-African orogenic movement formed the basement. From Caledonian orogenic movement in Carboniferous to Hercynian orogenic movement at the end of late Jurassic, the basin maintained craton-Mediterranean margin sedimentary characteristics. (2) In early Cretaceous, Neo-Tethys opened up, and the basin uplifted and characterized by a large-scale regression. Sirte basin subsided in late Cretaceous, and New-the Tethys sea rapidly invaded. Until Toulon age, ocean transgression further expanded. At the end of Eocene, the basin sank completely with a large-scale regression. (3) A small-scale transgression occurred late Oligocene; Sirte basin uplifted above sea level until late Miocene, and Pliocene and Quaternary deposits were thin or absent. Two large-scale transgressions of Neo-Tethys in early and late Cretaceous laid the foundation of good source rocks in the basin, fluvial sandstones formed by tectonic uplift in early Cretaceous, and the delta-coast or shallow marine sandstones and carbonatites formed by tectonic subsidence in late Cretaceous. Regional shales and local evaporites, formed by Neo-the Tethys sea sustained transgression in late Cretaceous, composed well regional caps. Therefore, upper Cretaceous petroleum system was the dominant, lower Cretaceous petroleum system as the secondary, and the Hercynian unconformity and faults as the main petroleum migration channels in the hydrocarbon accumulation groups. by September 2021, the 2P recoverable reserve of residual oil, natural gas and condensate in Sirte basin were 5420 million BBL, 32.5Tcf and 920 million BBL respectively.