川中震旦系-下寒武统有机质的生物标志物与稳定碳同位素特征及对比

Characterization of biomarkers and stable carbon isotopes of organic matters in ancient sedimentary rocks is a powerful tool for studying the petroleum potential and evolution of early life and environment. Source rock samples and reservoir samples which contain abundant solid bitumens from the Sinian-Lower Cambrian sedimentary sequence in central Sichuan will be collected. Signatures of biomarkers and compositions of stable carbon isotopes of their indigenous organic matters which will be obtained by using Soxhlet extraction and catalytic hydropyrolysis (HyPy) of kerogen/solid bitumen will be investigated. Biomarkers in saturated and aromatic hydrocarbons will be qualitatively and quantitatively analyzed by using gas chromatography-mass spectrometry (GC-MS) and metastable reaction monitoring/GC-MS (MRM/GC-MS) combined with co-elution and addition of internal standards. Stable carbon isotopes of kerogen and extracted bitumens, of individual compounds such as n-alkanes and isoprenoids will be determined by using Flash HT/GC-isotope ratio mass spectrometry (Flash HT/GC-IRMS) combined with molecular sieves. The source for initially existed oils in the Sinian-Lower Cambrian reservoirs can be determined by comparison of biomarker and carbon isotope compositions in source rocks with those in reservoir solid bitumens. Moreover, the evolution of biomarker and stable carbon isotope compositions in the Sinian-Lower Cambrian sedimentary sequence can help to understand the characteristics and formation background of organic matters in the ancient source rocks. In addition, comparison of biomarker and stable carbon isotope compositions of organic matters in the Sinian-Lower Cambrian sedimentary sequence in central Sichuan with those in other areas of the world (e.g., Eastern Siberia craton) may provide useful information on the evolution of the ancient life and environment during the Sinian-early Cambrian period.

古老地层有机质的生物标志物与稳定碳同位素特征是研究油气资源潜力及早期生命与环境演化的有力工具。采集川中震旦系-下寒武统烃源层和储层岩心（富固体沥青）样品，应用索氏抽提和干酪根/固体沥青催化加氢热解获取原生有机质。借助色谱-质谱和亚稳态反应监测/色谱-质谱，采用标样共注和内标法，进行有机质饱和烃和芳烃生物标志物的定性定量分析；借助元素分析/色谱-同位素比值质谱，采用分子筛络合法，测定干酪根和抽提沥青等全组分、正烷烃和类异戊二烯烃等单体烃的稳定碳同位素。对比烃源层和储层固体沥青的生物标志物与稳定碳同位素特征，判断古油藏油气来源；建立烃源层有机质生物标志物与稳定碳同位素特征剖面，探讨有机质类型、生源及富集环境的演化特征；对比四川盆地同全球其他地区（如俄罗斯东西伯利亚克拉通）震旦系-下寒武统有机质生物标志物与稳定碳同位素特征的异同，探讨导致其异同的原因及对震旦纪-早寒武世时期生物与环境演化的启示。

本项目系统采集川中震旦系-下寒武统烃源层和储层（富固体沥青）样品基础之上，开展了有机质生物标志物与稳定碳同位素特征的精细刻画与对比。结果表明，研究区灯影组储层岩心样品中含有丰富的固体沥青，采用溶剂萃取法提取。固体沥青是由储层中早期充注的原油经热裂解蚀变形成，前人研究认为早期充注的原油来自于埃迪卡拉纪-寒武纪早期发育的烃源岩。基于菲类和芳香甾族化合物的成熟度参数，储层固体沥青萃取的烃类热演化程度非常高，这与它们所赋存的储层深度及温度是一致的。储层可溶沥青具有非常相似的生物标志物特征，包括：无环类异戊二烯烃相对丰度很高，且姥鲛烷/植烷比值<1；存在甲基和乙基甾烷以及高丰度的2-甲基藿烷；C27-29规则甾烷丰度高，具有轻微的C27或C29优势。藿升烷系列及甲基藿烷的存在指示原核细菌对有机质的贡献，而甾烷类包括规则甾烷和甲基甾烷表明真核藻类的输入。基于三环萜烷分布样式、二苯并噻吩/菲比值、C27重排甾烷/(重排甾烷+规则甾烷)等参数，表明古油藏烃源岩以页岩为主要类型，但不能完全排除混合的页岩-碳酸盐岩烃源。C30去甲基甾烷、低姥鲛烷/植烷比、高伽马蜡烷指数、28,30-二甲基藿烷和2-甲基藿烷的存在表明烃源岩沉积于水体分层、缺氧、高盐度的海洋环境。此外，储层固体沥青可溶有机质芳烃类中含有异常高含量的多环芳烃化合物，如荧蒽、芘、苯并[a]蒽、䓛、苯并荧蒽、苯并芘等，且其中多环芳烃化合物丰度远高于其烷基取代异构体丰度。芳烃类化合物组成特征指示固体沥青的成因与异常热事件有关，如热液改造作用，该结论与其他研究结论相吻合。