原油组分Re-Os放射性同位素体系特征及其定年机理与应用启示

Characteristics of the Re-Os Radiogenic Isotope System of Crude Oil Fractions and Its Dating Mechanism and Applications

Re-Os放射性同位素体系可用于含油气系统关键地质过程的定年与示踪研究。不过,Re-Os定年的精度仍受到有关科学问题的制约,如原油组分的Re-Os体系特征、沥青质渐进散失对原油Re-Os体系特征与定年应用的影响等。本研究通过二元溶液直接分离原油次组分的实验,揭示了原油组分的Re-Os体系特征,模拟了实际地质情况中沥青质渐进散失对原油Re-Os体系特征与定年应用的影响,并通过重复实验验证相关实验流程对所取得的结果和认识的影响。研究发现,根据沉淀的先后顺序,原油次组分的Re和Os元素丰度总体上呈下降趋势,但有起伏变化,Re-Os同位素比值则单调下降。因此,沥青质的渐进散失将导致原油Re和Os元素丰度以及Re-Os同位素比值降低,进而对原油和低成熟度沥青Re-Os定年与示踪的应用产生影响。重复实验表明,实验室分离次组分的操作结果具有一定的随机性,但不影响Re-Os体系的总体性质。

The Re-Os radioisotope system can be used for isotopic dating and tracing key geological processes of petroleum systems.However,the precision of Re-Os dating of crude oil is still constrained by factors such as the characteristics of the Re-Os system of crude oil components and the gradual loss of asphaltenes.This study directly separated crude oil fractions by using binary solvent mixtures,revealed the characteristics of the Re-Os system of the crude oil components,and simulated the impact of gradual asphaltene loss on the application of Re-Os dating of crude oil in practice.Repeated experiments were conducted to verify the impacts of the experimental procedures on the results and their interpretation.It was found that according to the order of precipitation,the abundances of Re and Os in fractions of crude oil showed a decreasing trend on the whole,but there were fluctuations,and the Re-Os isotope ratios decreased monotonically.Therefore,the gradual loss of asphaltenes will lead to a decrease in the Re and Os abundances and Re-Os isotopic ratios of crude oil,which will further affect the application of Re-Os dating and tracing for crude oil and low-maturity bitumens.The repeated experiments showed that the results of the laboratory separation of the fractions have a certain randomness but do not affect the overall properties of the Re-Os system.