Geochemical Characteristics of Some Oils Derived from Lacustrine Sediments, China

R. P. Philp, H. Zhu, P. Fan

A large proportion of oils occurring in China are derived from sediments deposited in lacustrine environments whose salinities range from hypersaline to freshwater. Variations in the salinities of the environments will, to a large extent, determine the nature of the organisms that predominate within the water column. This in turn will affect the chemical composition of the sediments and ultimately the composition of the oils generated from the sediments.

A large number of oils and source rocks from various lacustrine basins in China, including the Tarim, Kelaymai, Jianghan, Shannganning, and Chaidamu basins, have been examined and characterized by a variety of organic geochemical techniques including gas chromatography, gas chromatography-mass spectrometry, and pyrolysis-gas chromatography and pyrolysis-gas chromatography-mass spectrometry for characterization of the asphaltenes.

The results from these experiments illustrate biomarker distributions characteristic of lacustrine environments such as high gammacerane and ß-carotane concentrations, high tricyclic terpane concentrations in the hypersaline environments, and an apparent increase in the ^dgr¹³C values of the oils with increasing salinity. Samples from the more hypersaline environments also show very high phytane concentrations relative to pristane and a pronounced even/odd predominance of n-alkanes. The unusual distributions of the organosulfur compounds in the samples are significant. It is anticipated that the final outcome of this study will be to provide a series of biomarker parameters that can be used to describe lacustrine environments of varying salinities.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.