Oil Window in the Gulf of Suez Basin, Egypt

Ahmed Nabil Shahin

Petroleum in the Gulf of Suez is multisourced mainly by restricted marine Cretaceous to Eocene beds. The Campanian carbonates of the Sudr Formation and the Turonian shales of the Abu Qada Formation are high-quality sources. Other proven sources are carbonate and shale intervals within other sub-Miocene formations.

Geothermal modeling calibrated by maturation measurements suggests that the organic-rich lower Miocene marls may not be mature enough to expel hydrocarbons north of the Morgan-Amal fields area but are mature to the south. This could be related mainly to a gradual increase in thermal gradient from north to south (20-55°C/km). A few anomalies do exist, however. Thermal gradients are generally higher in areas where oil accumulated. The depth of peak generation ranges between 5,200 m to the north and 3,300 m to the south.

The geographic variations in heat flow, maturation depths, and age of source rocks are not reflected in the timing of hydrocarbon migration. During the middle Miocene, a short-lived salinity crisis resulted in the deposition of massive thick evaporites that form the ultimate seal in the Gulf. The accompanying rapid burial of the underlying sub-Miocene potential source intervals caused them all to sequentially enter the oil window, within a very short time, soon after the evaporites accumulated. This timing was perfect for hydrocarbon preservation: after seal deposition and major disturbing regional tectonic events. The almost simultaneous migration from all the source beds resulted in mixed multisourced hydrocarbon accumulations.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.