--> ABSTRACT: Geochemical Evaluation of a Rapidly-Subsiding Basin: South Caspian Basin, by Michael A. Abrams, Ibrahim S. Guliev, and James W. Collister; #90906(2001)

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Michael A. Abrams1, Ibrahim S. Guliev2, James W. Collister1

(1) University of Utah Energy and Geoscience Institute, Salt Lake City, UT
(2) Geological Institute of Azerbaijan, Baku, Azerbaijan

ABSTRACT: Geochemical Evaluation of a Rapidly-Subsiding Basin: South Caspian Basin

The South Caspian Basin contains significant accumulations of both oil and gas-condensate within upper Miocene to Pliocene Productive Series as a result of a unique set of paleogeographic and tectonic events. Regional uplift led to deposition of extensive late Oligocene to middle Miocene oil and gas prone organic rich source rocks. Rapid Pliocene subsidence resulted in thermal disequilibrium, extensive migration pathways, entrapment of early biogenic gas, multiple hydrocarbon charges, and differential hydrocarbon entrapment/loss.

The reservoired crude oils belong to a single genetic oil group with molecular characteristics consistent with a marine clastic source facies. Significant variations in oil properties suggest post-emplacement bacterial and fractionation alteration, and multiple stage charging. Hydrocarbon seeps also belong to this oil group extending the working hydrocarbon system beyond current well penetrations. Reservoired gases have been sourced from mixed terrestrial-marine source facies generated at peak oil temperatures with varying contributions of biogenic gas.

Source rocks capable of generating significant volumes of both oil and gas can be found in onshore outcrops and cores from the Eocene to Middle Miocene. No Upper Miocene or Pliocene potential source rocks have been detected. Extracts from Maikopian and Diatomaceous rocks display similar molecular characteristics as reservoired oils and seeps, but also display an isotopic separation by reservoir age. A similar isotopic separation was noted in Lower Maikopian to Diatomaceous rock extracts indicating offshore oils (Pliocene reservoirs) are primarily derived from Upper Maikopian and Diatomaceous rocks whereas onshore oils (Miocene and older reservoirs) are derived from Lower and Middle Maikopian rocks.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado