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

Petroleum mainly comprises carbon and hydrogen elements. The stable carbon isotopic analysis for whole oil was undertaken as early as the 1930s. After decades, the stable carbon isotopic analytical methods have been developed from analysis for whole oil and oil fractions (e.g., saturated, aromatic and polar frac-tions) into compound-specific isotopic analysis with the emergence of the newly developed GC-C-IRMS analytical technique. Especially, by using com-pound-specific isotopic analytical…

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

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 δ D 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 δ D 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 δ D values of individual n-alkanes in crude oils from Lunnan Oilfield.