--> Abstract: Tectono-Stratigraphic Evolution of the North Western Desert, Egypt: Implications for Hydrocarbon Prospectivity, by M. El Toukhy, A. Mahmoud, A. N. El-Barkooky, and S. Gouda; #90923 (1999)

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El TOUKHY, MOHAMED, Shell Egypt N.V.; ASEM MAHMOUD, Bapetco; A.N. El-BARKOOKY,* Cairo University; and SAID GOUDA, Shell Egypt N.V.

Abstract: Tectono-Stratigraphic Evolution of the North Western Desert, Egypt: Implications for Hydrocarbon Prospectivity

The North Western Desert area in Egypt is situated at the northern edge of the African Craton adjacent to the Mediterranean basin (Fig. 1).The improved understanding of the stratigraphic and structural patterns and their inter-relations is helping to evaluate the remaining hydrocarbon prospectivity.

The tectonic-stratigraphic model, presented here for the northern part of the Egyptian Western Desert, is based on a large well and seismic database, including high-resolution data. Four tectono-stratigraphic episodes have been identified (Fig. 2), which can be related to large-scale crustal movements.

During the Paleozoic, mild tectonism prevailed, characterized by broad tabular uplifts and block faulting. This resulted in the development of extensive shelf platforms and some shallow epicontinental basins. The hydrocarbon potential of the Paleozoic sequences is mainly associated with broad, but subtle structural traps.

In the Triassic to Early Jurassic times, the break-up of Pangaea and progressive opening of the Neo-Tethys were associated with the development of extensional intra-cratonic rift basins. The structural orientations were mainly NE, E-W and WNW. The southern rim and the rift shoulders of the uplifted broken African continental shelf were rimmed by fluvial sandstones. The rift basins were filled in the early stage by estuarine deposits, which were sand-rich in many places due to the active syndepositional tectonics. Shallow marine shales and carbonates subsequently draped the sandy estuarine fills providing perfect seals as well as source rocks. To the northwest, newly compiled information about the structural and depositional history of major hydrocarbon provinces, indicate a rift-related depositional regime. Better understanding of the Mesozoic paleogeography and the distribution of incised valley fills are instrumental in the prediction of reservoir distribution.The Obaiyed gas field is a good example, with a stratigraphic trap component provided by an estuarine embayment fill of Early Middle Jurassic age. By the Middle to Late Jurassic, the tectonic relief had disappeared and extensive platform carbonates were deposited.

Between the Late Jurassic and the Tertiary, successive phases of rotation and collision between the African Plate and Eurasia controlled structuration and basin development. Shelf conditions resumed throughout the Middle to Late Cretaceous with mixed clastics/carbonate platform deposition. Intra-Cretaceous mild compressional tectonic phases are recognized as local unconformities. These culminated in a major regional angular unconformity (Fig. 3) at the Cretaceous - Tertiary boundary, indicating a Late Cretaceous (Campanian-Maastrichtian) structuration climax associated with both compressional and wrench tectonics.

Recent seismic data shows the Mesozoic sequence extending northwards offshore into the Mediterranean. At the shelf edge it is downthrown some 4km into the Mediterranean basin where it is overlain by a thick, unexplored, probably Tertiary sequence. Potential hydrocarbon traps in this sequence are associated with gravitational tectonics.

The proposed tectonic-stratigraphic models not only assist in the exploration of the conventional plays in the Western Desert, but also in the prediction of more unconventional play such as subtle stratigraphic/structural Mesozoic traps.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England