SCHWANDER, MARCUS,AHMED ABDEL AAL,AHMED EL BARKOOKY, MARC GERRITS, HANS MEYER, and HALA ZAKI, Shell Egypt Deepwater B.V., Cairo Egypt

Abstract: The Nile Delta Ultra-Deep Water Area of the Eastern Mediterranean Basin.

Exploration of the ultra-deep water area off the Nile Delta in water depths ranging from 800-2800m is underway. Some 7000 km of seismic data have been acquired in early 1999, covering most of the area for the first time and recording sedimentary sequences down to 8 seconds. Exploration will continue with the acquisition of 3D seismic leading to exploration drilling in 2001. Initially, the challenge is to identify the main plays by integrating the seismic with new gravity and aeromagnetic data and in particular to delineate areas where turbidite sands are best developed and have highest potential to trap hydrocarbons. The search for high performance turbidite reservoirs includes identification and characterisation of the diverse turbidite geometries from seismic and the classification of the local turbidite depositional system.

The area is located in the southeastern Mediterranean basin and covers the Nile Cone between the Herodotus abyssal plain in the west and the Levant basin in the east (Fig. 1a). The complex evolution and interaction of the African, Eurasian and Arabian plates have shaped the Upper Miocene to Recent Nile Cone and its substratum. In particular the structural evolution of its northwestern part appears to be closely related to the collision of the Eratosthenes seamount with the Cyprus active margin.

The tectono-stratigraphic framework is controlled by deep-seated basement structures with distinct gravity and magnetic expressions and by the interference of two major fault zones, namely the NW-SE trending Misfaq-Bardawil zone and the NE-SW trending Qattara-Eratosthenes zone (Fig. 2). Superimposed on this, a Messinian evaporitic sequence up to 4 km thick caused significant salt-induced deformation (salt ridges, diapirism and collapse structures) and large-scale rotational block movement (Fig. 1 b-c). The latter appears to have been triggered by basement uplift at depth and occurs along the southern margin of the Messinian salt basin, the trend of which parallels the Mediterranean active margin between Cyprus and the Crete islands.

The identified deformational pattern is to a large extent the result of multi-phase tectonic movement along pre-existing basement faults of the Neo-Tethys continental margin. Along the NE-SW Qattara-Eratosthenes trend, major Late Cretaceous to Early Tertiary transpressional structures are onlapped and covered by an up to 3 km thick pre-salt sequence (Fig. 1b and 1c). These sequences are interpreted as Late Paleogene to Late Miocene in age, consisting predominantly of deepwater sediments with local condensed sequences over the syndepositional intra-basinal highs.The late Miocene pre-salt sequence appears to shale out westwards across the Qattara/Eratosthenes trend. Here, the sequence appears to be heavily deformed by mud diapirism and gravitational faulting. Complex deformation occurred along the NW-SE Misfaq-Bardawil line (Fig. 1d) with dominant fault movement in Late Tertiary to recent times. This is associated with large-scale north-vergent uplift, the inversion of the salt basin along the Eratosthenes high and recent strike slip faulting, most intense in the Levant area.

The Messinian depositional system envisaged is that of a Platform-Canyon-Canyon Front setting passing northward into the salt basin.The evaporitic sequence exhibits three distinct seismic facies suggesting cyclic deposition with the occurrence of interbedded anhydrite, salt and clastic sequence and of pure halite deposition.Associated with the Messinian salinity.crises, large-scale canyons were excavated resulting in multiphase cut-and-fill clastic systems.

The Plio-Pleistocene sequences were deposited in a slope to basin floor setting. Basin-fill models calibrated by detailed sequence stratigraphic analysis in the explored part of the Nile Delta predict a variety of turbidite environments. Syndepositional fault movement and mobile salt created confined turbidite settings with the development of mini-basins with local sediment-ponding. In strike, these settings coexist with a graded-slope, where unconfined turbidite deposition occurred in slope channel systems with the potential for sheet sands to be deposited along fault-induced depressions.

Exploration targets are the Plio-Pleistocene deepwater channel and basin floor turbiditic sands likely to occur in a variety of structural settings.The Upper Miocene sequence offers additional exploration objectives in the form of fluvial and/or turbidite sands, deposited in the platform, canyon and canyon-front settings.The focus of pre-salt exploration is the delineation of distal turbidites within the Serravalian to Tortonian sequence and to identify new reservoir sequences deposited over and along the pre-existing intrabasinal highs. Hydrocarbon charge has yet to be proven by drilling, but seismic amplitude anomalies and the occurrence of natural surface slicks suggest both gas and liquid charge from pre-salt source rocks through faults and salt withdrawal windows.

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