Molecular and Isotopic Composition of Natural Gas Discoveries, Western Offshore Nile Delta, Egypt

Claudius Vandré¹, Bernhard Cramer², Peter Gerling², and Jutta Winsemann^1
1 Universität Hannover, Hannover, Germany
² Federal Institute for Geosciences and Natural Resources, Hannover, Germany

The prolific gas/condensate province of the Nile delta area is situated at the north-eastern edge of Egypt representing the SE part of the Eastern Mediterranean basin. Despite intensive exploration activities the hydrocarbon system is still poorly understood. To identify generation mechanisms and sources of the natural gas 19 test gas samples (kindly supplied by RWE Dea Egypt and BP Egypt) from the Neogene section of six offshore wells have been analyzed for their molecular and isotopic composition. Main constituents of the gas are hydrocarbons up to pentane with traces of carbon dioxide and nitrogen. Methane as dominating component (> 91 vol. %) is characterised by a d13C between -43 and -55 ‰ and a dD ranging from -163 to -177 ‰ arguing for a mixed thermogenic and microbial origin. Geochemical characteristics suggest that the thermogenic hydrocarbons are genetically related to the same type of source rock probably distinguished by a mixed type II/III kerogen. It's supposed, that this primary source of gas and condensate in the Nile delta is represented by rocks of the Oligocene to Early Miocene sedimentary sequence. Some Mesozoic intervals known from the onshore part of the delta and from the Western Desert may act as additional sources. In addition to the process of microbial gas generation by decomposition of sedimentary organic matter, isotope geochemical data support the hypothesis of methane generated from microbial degradation of trapped thermogenic hydrocarbons.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005