--> Abstract: Mud Volcanoes from de Nile Delta (Deep Offshore Egypt): Nature and Origin of the Fluids, by Eric Deville, Alain Prinzhofer, Jean-Paul Foucher, Jean Mascle, and Jean-Claude Caprais; #90072 (2007)

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Mud Volcanoes from de Nile Delta (Deep Offshore Egypt): Nature and Origin of the Fluids

Eric Deville1, Alain Prinzhofer1, Jean-Paul Foucher2, Jean Mascle3, and Jean-Claude Caprais2
1Institut Francais du Petrole, Rueil-Malmaison, France
2Ifremer, Plouzane, France
3Geosciences Azur, 06235 Villefranche-sur-Mer, France

The Nautinil cruise allowed submersible sampling of macro-seeps in the deep Nile delta. The solid fraction transported within the expelled mud has different origins, and includes notably fragments issued from below the Messinian salt. Fluids are rich in gas solubilized in water and includes locally free gas bubbles (North Alex and Isis mud volcanoes). The gas chemistry, carbon isotopes and noble gas isotopes define three genetic families: (1) thermogenic gases, without any post-genetic fractionation (Napoli, Isis, Osiris and North Alex volcanoes). They are generated in deep petroleum systems, and are collected after their upwelling to the surface, (2) bacterial dry gases, with isotopically very light methane (Amon volcano, Menes Caldera). They are probably generated in shallow horizons in the sediments, and (3) gases with intermediate compositions, corresponding to either a mixing between thermogenic and bacterial gas, or to gases fractionated during their uplift (Kheops and Kephren volcanoes). For the thermogenic gases, genetic parameters as source-rocks and maturity could be characterized: Osiris gas is clearly more mature than Isis. North Alex corresponds to a gas of low maturity, generated from a different source-rock. Napoli, (within the Mediterranean ridge, south of Crete) is associated to a different source-rock. No evidence of any biodegradation could be observed (lack of fractionation for propane and normal-butane), proof that gas seepage is quick enough to prevent any alteration. For the first time, noble gas isotopic patterns were performed in offshore gas seeps. The Kephren and North Alex gases show a longer residence time, indicating an important thermogenic contribution. The Isis gases present a residual signature, indicative of an important leakage of the associated deep hydrocarbon reservoir.

 

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece