油气藏铼-锇同位素定年的进展与挑战

Rhenium-osmium geochronology in dating petroleum systems:progress and challenges

铼(Re)、锇(Os)元素具有对氧化还原的敏感性和亲有机质特性,富集于烃源岩、油砂、原油、沥青等油气藏相关地质样品中,并被用于油气藏同位素定年。该方法既可通过Re-Os等时线直接获取油气成藏过程的绝对地质年龄,又可利用Os同位素初始值开展油源对比。分析近十余年来油气藏Re-Os同位素年代学研究的进展与不足,指出为推动该定年技术的发展及其在油气勘探实践中的应用,学术界和工业界应密切合作共同探索Re-Os同位素在油气系统中的分馏机理,全面评价硫酸盐热化学还原反应(TSR)、热解事件等后期地质过程对Re-Os同位素体系的潜在影响;综合运用无机和有机地球化学方法,建立判别油气来源的有效工具,以帮助合理选择满足同源特征的Re-Os同位素定年对象。这些问题的解决将有助于尽快建立油气藏Re-Os同位素定年的实用技术方案,并为业内的终端用户提供完整的使用指南。

Re and Os are redox-sensitive and organophilic,and can be enriched in potential hydrocarbon source rocks,tar sands,crude oil,and bitumen.Re-Os geochronology of these organic-rich samples has the potential for direct dating the time frame of hydrocarbon formation,migration or charge within a petroleum system.Moreover,the initial 187 Os/188 Os composition can also be used to fingerprint oil-oil and oil-source rock correlations.Here,we review some major reported case studies on the Re-Os geochronology of oil and gas reservoirs over the last decade.Through evaluating the advancements and shortcomings in Re-Os geochronology for petroleum system analysis,and considering the actual requirement of hydrocarbon exploration,we conclude that it is quite urgent to investigate the detailed behavior and fractionation mechanisms of Re and Os in a petroleum system,to evaluate the influence of TSR（thermochemical sulphate reduction）and thermal cracking on the Re-Os isotopes in hydrocarbons,and to establish a more reliable and efficient inorganic-organic geochemical tool allowing effectively fingerprint the fate of petroleum from its source to trap,and for oil-oil correlations.Filling the above knowledge gaps requires a comprehensive academia-industry collaboration,which is critical step to accomplish a valuable application guide for the petroleum industry end-users on using the Re-Os isotope system to directly date petroleum systems.