摘要
Re和Os易于被有机物捕获而富集,并长期稳定地保存在烃源岩、原油和沥青中而保持良好的封闭体系。可以对烃源岩、原油和沥青进行Re-Os同位素直接定年,获得与油气成藏相关的精确的绝对年龄信息。Re-Os同位素实验分析包括样品的溶解、Re和Os的化学分离与纯化、Re和Os同位素的质谱测定。原油中沥青质组分的Re,Os同位素组成能够近似代表全油的Re,Os同位素组成,对原油进行Re-Os同位素分析实质就是对原油中的沥青质组分中的Re-Os同位素体系进行分析,其年龄记录的是油气生成的年龄,原油和烃源岩的187 Os/188 Os比值的对比可以进行油源示踪。沥青Re-Os同位素等时线年龄揭示的是油气大量生成运移的时间,年龄数据分散的主要原因是具有不同187 Os/188 Os初始比值的烃源岩对Re-Os体系的贡献。川西龙门山北段矿山梁下寒武统沥青Re-Os同位素组成和等时线年龄指示了油气生成和运移的时间发生在～164 Ma,并来源于两种烃源岩。Re-Os同位素体系的封闭性、等时线年龄的精度和油气地质意义、烃源岩多期熟化作用和混源作用的影响等方面还值得进一步深入研究。Re-Os同位素方法将在油气成藏年代学领域,特别是在碳酸盐岩地区的油气成藏定年方面具有广泛的应用前景。
Re and Os concentrate in organic matter and remain stable in source rocks for a long time,therefore,crude oil and bitumen can keep in a good closed system.Accordingly,study of Re-Os isotope system of source rocks,crude oil and bitumen can obtain the absolute dating of hydrocarbon accumulation,which has become a new research discipline in the field of hydrocarbon generation and accumulation geochronology.Re-Os isotope experimental analyses consist of sample dissolution,Re and Os chemical separation and purification,Re and Os isotope mass spectrometry measurements.Re and Os isotopic compositions of asphaltene fractions of crude oil are similar to that of whole oil.The essence of Re-Os dating for crude oil is to analyze the Re-Os isotope system for asphaltene fractions of crude oil,and the age obtained records the timing of petroleum generation and migration.The 187Os/188Os composition of oil can provide information on its source and the bitumen Re-Os isochron ages yield the timing of petroleum generation and migration.Initial 187Os/188Os ratio of bitumen derived from migrated hydrocarbons are due to different source rocks and also resulted in very high scatter value for the regression of Re-Os bitumen data.The Re-Os isotopic analyses for Cambrian bitumen of the Kuangshanliang in the north Longmenshan belt indicate that the timing of petroleum generation and migration occurred at ~164 Ma and the bitumen are derived from two kinds of source rocks.Therefore,the closure of the Re-Os isotopic system,the precision of Re-Os isotopic isochron age and its significance for hydrocarbon accumulation,the multi-phase maturation of the source rock and different source rock mixture effects are worth further studied.Re-Os geochronology and source tracing should become a powerful tool in the field of hydrocarbon accumulation geochronology,especially for the dating of hydrocarbon accumulation in the carbonate region,and will have significant application in the near future.
出处
《矿物岩石》
CAS
CSCD
北大核心
2011年第4期87-93,共7页
Mineralogy and Petrology
基金
中国石油科技创新基金(2009D-5006-01-08)
国家自然科学工青年基金(40902038)
湖北省自然科学基金(2009CDB217)
关键词
RE-OS同位素体系
油气成藏
原油
沥青
烃源岩
Re-Os isotopic system
hydrocarbon accumulation
crude oil
bitumen
source rocks
