The infrared absorption spectrometer is a powerful tool for detecting functional groups of organic compounds and analysing their molecular struc-tures.Since sixties

this tool has been adopted into areas of petroleum geology and a great quantity of data were achieved.A lot of facts demons-trate that the infrared spectrum of crude oil from various districts or differ-ent horizons exhibits both common and peculiar features

and it indicates some difference in geological settings.The main factors that lead to the above difference in properties of crude oil in China proper are as follows:(1)Source bed which may be of sapropelic or humic type;(2)Sedimentary and oil-generating environment which may have affectedon conservation

trans formation and maturity of organic substances;(3)Epigenetic changes of crude oil which may account for subsequente volution

oxidation

biological and physical processes.Majority of oil fields in China discovered now are concentrated in Mesozoic and Cenozoic continental basins

thus the source beds mostly are of mixed sapropel-humic type.The crude oil generated contains generally more high-molecular paraffin

aromatic and polycyclic naphthenic hydro-carbons and

moreover

was not deeply buried

but well concealed and underwent only a little of epigenetic alteration All these account for the displaying high absorption peaks of its infrared spectrum for high mole-cular paraffin and aromatic hydrocarbons.However

in places where it was deeply buried or the ancient geotherms were higher

it underwent to a cer-tain degree modification and therefore shows an infrared spesctrum oflight crude oil.Depending on geological setting of petroleum productive basins

the crude oil of individual basins may possess different infrared spectrum.In the continent of our country

there are relatively small amountsof oil and gas fields in marine sediments.The source beds generally are of sapropelic type and the crude oil derived there from is represented chiefly by alkanes and naphthenes which have lower molecular weight

but the aromatic hydrocarbon and high-molecular paraffin are rarely cantained.Further more

because of its aging

being deeply buried and extensive modi-fication

it usually has infrared spectrum with a nature of light crude oil which accounts for more intensive absorption peaks for methyl

methy leneand lower molecular alkanes and indistinct absorption peaks for aromatic hydrocarbon and heterocyclic compounds.Local crude oil maintains solidparaffin or has become oxidized heavy oil with entirely different infrared spectrum.