Abstract: Petroleum Geochemistry of Upper Permian and Middle Jurassic Source Rocks and Oils of the Turpan-Hami Basin, Northwest China

Preliminary bulk and molecular geochemical analysis can distinguish between two main petroleum systems, consisting of both Upper Permian mudrocks and Middle Jurassic coals, in the Turpan-Hami basin, a large incompletely explained petroliferous basin in northwestern China. Although the Turpan-Hami basin contains many producing oil and gas fields and ranks among the top nonmarine basins in coal accumulations in the world, no study to date can unequivocally identify the source rock facies for Turpan-Hami's produced oils. This study, however, reports preliminary high resolution biomarker results of two good oil-to-rock correlation models for both Middle Jurassic coals and Upper Permian mudrocks.

First, using diterpane and terpane distributions, source prospective Middle Jurassic coals (Rock-Eval Hydrogen Index (HI)=1012 mg hydrocarbons (HC)/gm; S2=123 mg HC/gm) correlate well with 9 oils from the main producing region in the Tabei Sag. Second, although the sample set is small, organic-rich Upper Permian mudrocks (HI=500; TOC=8.2%) from the southern depression (Tainan Sag) match well with oils in both the southern and western (Tokesun Sag) depressions. In addition, diterpane distributions of phyllocladanes, isopimeranes, and rimuanes in source rocks and oils appear to successfully discriminate between source lithologies (coals from mudstones) as wells as age (Permian vs. Jurassic). This ongoing geochemical study, combined with a complimentary petrographic coal maceral study, will not only contribute to the global database of terrestrially sourced oils, but it will also address the controversial question of whether coals can be effective generators and expellers of liquid hydrocarbons.

AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid