Compound specific carbon isotope composition of light hydrocarbons in crude oils from the north of the Northern Tarim Uplift

Compound specific carbon isotope compositions of different fractions and different original crude oils were analyzed to investigate light hydrocarbon characteristics of crude oils in the north of the Northern Tarim Uplift.Compound specific carbon isotope divergences of cyclopentane compounds in different crude oils were the least,which indicated that cyclopentanes had poor diagnosis in light hydrocarbons.A significant law can be found by compound specific carbon isotope compositions of optimized light hydrocarbons.Compound specific carbon isotope of light hydrocarbons in coal-formed oils from the Luntai Oilfield was the highest,ranging from -21‰ to -19‰.Lacustrine oils from the Dalaoba Oilfield took the second place,ranging from -25‰ to -21‰.Marine oils in the Yakela Oilfield were the lowest,ranging from -31.5‰ to -28‰.Compound specific carbon isotope composition of light hydrocarbons in crude oils which derived from Cambrian-Lower Ordovician in well YN2 was unique.It is suggested that compound specific carbon isotope composition of light hydrocarbons can be a diagnosis index for group crude oil,especially for gas-condensate and light oils.