--> ABSTRACT: Origin of Natural Gases of Giant Gas Fields of West Siberia in the Light of New Data, by M. Schoell, F. J. Picha, N. Nemchenko, and A. Rovenskaya; #91021 (2010)

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Origin of Natural Gases of Giant Gas Fields of West Siberia in the Light of New Data

SCHOELL, MARTIN, FRANK J. PICHA, NICOLAY NEMCHENKO, and ALLA ROVENSKAYA

Gases in NW Siberia can be stratigraphically grouped into Cenomanian age gases, which are (with few exceptions) dry gases (C2+ approx.= 0.04 to 0.18 percent; delta{13}C1 approx.= -65.4 to approx. -50 o/oo; deltaD1 approx.= -250 to -210 o/oo) and Pre-Cenomanian gases (C2+ approx.= 0.3 to 30 percent; delta{13}C1 approx.= -49 to -32 o/oo; delta{13}C2 approx.= -30.5 to -26.6 o/oo; delta{13}C3, 4 approx.= -29.8 to approx.= -25.3 o/oo; deltaD1 approx.= -258 to -206 o/oo; deltaD2 approx.= -251 to approx.-213 o/oo; deltaD3 approx.= -221 to approx.= -182 o/oo). Only two of the analyzed gases on the northern Yamal Peninsula have carbon and hydrogen isotope values of -65.4 and -61.4 o/oo and -249 to -241 o/oo, respectively, both consistent with a bacterial origin. However, the majority of the Cenomanian gases in NW Siberia is isotopically from these bacterial gases, not only in Carbon but also in Hydrogen isotopes of methane which is inconsistent with a bacterial origin. The pre-Cenomanian gases in NW Siberia have Carbon isotope patterns typical for mature to post-mature gases with very little isotopic differences between ethane, propane, and butane, suggesting that these gases are primary cracking products of kerogens. The C2+ hydrogen isotope pattern of the pre-Cenomanian gases are similar to gases from coaly organic matter when compared to a worldwide database. We propose that the deep gases in NW Siberia are probably sourced to a large part from coaly sections in the Jurassic or pre-Jurassic and are not genetically related to the oils.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.