--> Abstract: Application of Carbon Isotopes of Monomeric Hydrocarbons in Petroleum Exploration in the Ordos Basin, by D. Jinxing, W. Zhang, X. Xia, L. Zhao, and C. Zan; #90937 (1998).

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Abstract: Application of Carbon Isotopes of Monomeric Hydrocarbons in Petroleum Exploration in the Ordos Basin

DAI, JINXING, ZHANG WENZHENG, XIA XINYU, ZHAO LIN, ZAN CHUANLI

The Ordos basin, as a large cratonic basin of poly-tectonic cycle and poly-sedimentary type, is characterized for its multiple petroleum-bearing beds and abundant resource, with gas dominating in Paleozoic and oil dominating in Mesozoic. Therefore, it's of great significance in exploration to study the source of Paleozoic gas and Mesozoic oil and to divide petroleum systems in this area.

Carbon isotopic compositions of petroleum, especially those of light hydrocarbon monomeric series, is one of the important foundations to distinguish the genesis and relation between petroleum and source.

In this study, carbon isotopic compositions of dozens of oil, gas and residual hydrocarbon in source rock samples from several era were analyzed by the method of GC/C/MS. Results show that, in oil and gas from each Mesozoic production(T3-J1), all of the monomeric light hydrocarbon series (C4-C8), normal alkane series (n-C5+), pristane and phytane have light carbon isotopic compositions. In light hydrocarbons, d13C values of i-alkanes vary between -30^pmil and -33^pmil, d13C values of methylcyclopentane are between -26.8^pmil and -28.7^pmil , d13C values of methylcyclohexane are -27.6^pmil ~-29.4^pmil, d13C values of n-C5+ are mainly between -30^pmil and -33^pmil, while d13C values of pristane and phytane are lower than -31^pmil, showing a typical oil-type oil of fresh-lake facies. The petroleum-source relation by monomeric hydrocarbon carbon isotopic composition show that oil and gas in T3-J1> beds come from the source rock of lake facies of late Triassic Yanchang Formation. Paleozoic oil and gas are rich in 13C, with d13C values of monomeric light hydrocarbon series mainly between -20^pmil ~-23.5^pmil, d13C values of n-C5+ heavier than -29^pmil and decreasing with carbon number, showing the characteristics of coal-type hydrocarbon and a main source of Carboniferous-Permian coal-measure mudstone.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah