Analysis of Carbon Isotopic Compositional Differences of Individual n-Alkane:Case study of Ordovician crude oil in Tahe oilfield
[Objective]To clarify the cause of the different compositions of the individual crude n-alkane carbon iso-tope(δ13Calkane)in the three categories,[Methods]in this study the composition of δ13Calkane in 17 Ordovician crude oil samples from the northern Tahe oilfield,combined with relevant organic geochemical parameters,were examined for depositional environment,maturity and biodegradation.[Results and conclusions]The differences in physical properties allows the crude oils in Tahe to be categorized as heavy,medium and light crude oils.The δ13Calkane value is between 37‰ and-31‰.It has the properties of marine crude oil,indicating that the composition and distribution of δ13Calkane are by the depositional environment and the type of parent material.Maturity gradually increases from heavy to medium to light crude oil,in turn leading to heavier δ13Calkane values,which is significantly higher in the lowcarbon-number part of the heavy crude oil.The heavy crude oil has been more strongly biodegraded than the medium and light crude oil,indicating that the degree of biodegradation is the main factor affecting the positive bias of δ13C14 to δ13C19 values of the medium-and low molecular weight n-alkanes in heavy crude oil.
carbon isotopic composition of individual n-alkanebiomarker compoundsmaturitybiodegradationTahe crude oil
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