Hydrogen isotopic compositions, distributions and source signals of individual n-alkanes for some typical crude oils in Lunnan Oilfield, Tarim Basin, NW China

摘要

Isotopic compositions of carbon-bound hydrogen in individual n-alkanes from several typical crude oil samples from Lunnan Oilfield, Tarim Basin, NW China, were firstly measured using newly developed gas chromatography-thermal conversion-isotope ratio mass spectrometry. The similar range of δD of individual n-alkanes of crude oils among reservoirs of different geological times reflects that hydrocarbons are all derived from the same marine depositional environment. Compared to the theoretic value (-150‰) and the reported δD values (nC13―nC27, -160‰―-90‰) of individual n-alkanes for Ordovician-sourced crude oils in the Canadian Williston Basin, the hydrogen isotopic composition of individual n-alkanes in crude oils from Lunnan Oilfield is characterized by heavy hydrogen isotopic values (nC12―nC27, -120‰―-60‰). In terms of the factors that control the fractionation of hydrogen isotopes, relatively saline depositional environment and higher thermal maturation were attributed to the heavy δD values of individual n-alkanes in crude oils from Lunnan Oilfield.