Natural gas formation in the western Nile delta (Eastern Mediterranean): Thermogenic versus microbial

Evidence for microbial alteration of petroleum accumulations in the Nile delta is largely manifested in anomalously heavy isotopic compositions of both wet-gas components propane and n-butane and preferential removal of higher n-alkanes from condensates. The hydrocarbon accumulations affected by biodegradation are trapped within shallow Pliocene reservoirs (<2400 m) where present day temperatures are below 80 °C. The coexistence of biodegraded thermogenic gas and condensate with dry microbial gas supports the concept that generation of secondary microbial methane by biodegradation of thermogenic hydrocarbons may occur within the Nile delta.