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Площадь: 653032.4 км²
Sirt Basin
The Sirt Basin is bordered in the northeast by the Cyrenaica Platform, in the west by the Ghadames Basin, in the southeast by the Al Kufrah Basin, in the southwest by the Murzuq Basin and in the north by the Mediterranean Sea (Fig. 1). It covers an area of approximately 400,000 km2 onshore and extends offshore into the Gulf of Sirt. The Sirt Basin belongs to the World’s top 20 petroleum provinces, having proven reserves of 43.1 billion BOE in 2002 (Ahlbrandt 2002). Early Mesozoic Neotethyan-related extension and volcanism was of limited effect and is represented by the Triassic Amal Formation (Hallett 2002; Guiraud et al. 2005). Broader structuration took place in the Aptian–Albian with deposition of the Sarir and Faregh sandstones and their lateral equivalents. This was most pronounced in the east–west trending eastern Sirt basins.
Fig. 1 Sirt Basin petroleum systems, Libya
The main phases of extension and subsidence, however, are distinctly Late Cretaceous to Cenozoic in age and have been well-documented by many authors (El-Alami et al. 1989; Wennekers et al. 1996; Baird et al. 1996; Anketell 1996; Selley 1997; Salem 2000; Hallett 2002; Burwood et al. 2003; Hassan and Kendal 2014). The onshore Sirt Basin is for the most part not affected by Late Cretaceous and Cenozoic inversion, rather being marked by a thick succession of post-rift sediments extending until the Miocene (Fig. 11; Abadi et al. 2008).
The Late Cretaceous Campanian Sirte Shale is the primary hydrocarbon source rock. However, delineation of eight end-member generic oil families by Burwood et al. (2003) indicates a number of complex contributory petroleum systems and mixed-system hybrid oils. Nonmarine lacustrine source inputs with increased waxiness have been recorded, perhaps arising from the Triassic and/or Early Cretaceous syn-rift strata. Source potential is also identified in the Rachmat-Tagrifet (Upper Cretaceous), Harash (Paleocene), and various Eocene formations.
Reservoirs range in rock type and age from fractured Pre-Cambrian basement (rarely), siliciclastics in the Cambrian–Ordovician Gargaf and Lower Cretaceous Sarir, to Paleocene Zelten Formation and Eocene carbonates commonly in the form of bioherms. Carbonate reservoirs, mostly Cenozoic, contain 42% of the petroleum; siliciclastics, mostly pre-Cenozoic age, contain 58%. The top individual reservoirs are Zelten carbonates (33%), Sarir sandstones (28%), and the older Gargaf/Hofra/ Amal sandstones (29%) percent (Ahlbrandt 2000c).
Structural traps contain about 68% of Sirt basin reserves, stratigraphic traps about 24%, and combination traps about 8%. Reefal carbonates tend to form the most important stratigraphic traps and are mostly Paleocene in age. Other stratigraphic traps include algal banks, facies changes, and lateral shale-out of calcarenites (Salem 2000). Multiple reservoirs are charged mostly by vertically migrating hydrocarbons along horst-block faults from Upper Cretaceous source rocks that occupy structurally low positions in the grabens. Post-rift evaporites in the middle Eocene provide an excellent seal for the Sirte-Zelten hydrocarbon system.
Timing of generation in the Sirt Basin is estimated from basin modeling as mainly Paleogene in age. Hydrocarbon generation commenced at about 50 Ma in the deeper basins, about 40 Ma in many other areas, and may continue to the Present-day (Ahlbrandt 2001).
Data source: Regional Geology and Petroleum Systems of the Main Reservoirs and Source Rocks of North Africa and the Middle East. D. Lučić and W. Bosworth. 2019
Следующий Бассейн: Kohat - Potwar Foldbelt