--> --> Petroleum System: From Thermogenic to Biogenic Stories in Nile Delta, Egypt

AAPG Africa Region, The Eastern Mediterranean Mega-Basin: New Data, New Ideas and New Opportunities

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Petroleum System: From Thermogenic to Biogenic Stories in Nile Delta, Egypt

Abstract

More than 60TCF of gas have been discovered in the east Mediterranean deep water (e.g. Aphrodite, Leviathan, Tamar & Zohr fields). According to a 2010 USGS report, this region has 112 TCF of natural gas and 1.4 bbls of recoverable oil. The Nile Delta and Levantine Oligo-Miocene basins are separated from onshore and near-shore Mesozoic age carbonate platform by a major hinge line from the South and East, while it is bounded from the North by the Subduction Zone. During Early Oligocene, the Nile drainage system was established and delivered huge amounts of sediment from the central African hinterland towards the Mediterranean. Oligo-Miocene clastic sequences were capped by evaporites that were deposited during the Messinian Salinity Crisis. In the Nile Delta area, the shallow and onshore areas were subject to subaerial exposure, erosion and deposition of clastic sequences via active fluvial systems of the Abu Madi Fm. Deposition of the Plio/Pleistocene delta was followed the early Pliocene flooding event and comprises several major discoveries in paralic reservoirs at the END and slope turbidites toward the WND. As these discoveries have mixed biogenic and thermogenic gases, understanding the basin petroleum system in terms of source presence, maturation and charge is vital to unleash its remaining thermogenic and biogenic potential. Though integrating the understanding of the reservoir systems and quality, and structure growth timing plays an important role in the basin petroleum system story. The current petroleum system understanding demonstrates the key differences and similarities between the different elements required for thermogenic and biogenic accumulations, and the crucial controlling factors (e.g. onset of generation, structure timing). The main similar elements, which are source rock distribution and facies, fetch area size, trap timing and growth through time, and reservoir facies are needed to explain the thermogenic and biogenic accumulations. The thermogenic accumulations are geographically discrete and thus can be termed as discontinuous accumulations; hydrocarbon distribution is complex and controlled by multiple factors. It has its unique source rock potentiality and capability to generate oil vs. gas, thermal stress maturation, charge focus and access in the relationship between the onset of generation and trap timing. Also affected by primary and secondary migration, the secondary can be for long distances and is driven by buoyant force. Biogenic accumulations could be big and controlled by temperature through time or biogenic window (20°-60°C), in relation to structure timing and growth through time. Migration is predominantly primary over short distances, while secondary migration is driven principally by buoyant forces. ACKNOWLEDGEMENT: Special thanks go to BP Egypt Exploration teams.