苏北盆地盐城凹陷朱家墩气藏凝析油中的金刚烷类及其意义

Diamondoid Hydrocarbons and Their Geochemical Significances in Condensate from the Zhujiadun Gas Reservoir in the Yancheng Sag

盐城凹陷朱家墩气藏盐参1井阜一段储层所产凝析油与该井上白垩统泰州组成熟烃源岩在各类生物标志化合物的分布与组成特征上具有较好的相似性,表明它们在成因上存在相关性,但生物标志化合物成熟度参数显示凝析油的成熟度明显高于所研究的烃源岩。烷基单金刚烷类是原油和烃源岩中一类具有高热稳定性的烃类化合物,其中双金刚烷系列的热稳定性高于单金刚烷系列。分析结果表明：凝析油中不但存在烷基单金刚烷系列,同时也存在烷基双金刚烷系列,但在上白垩统泰州组烃源岩中仅检测到烷基单金刚烷系列,烷基双金刚烷系列不但不完整且丰度很低,这一现象表明原油的成熟度明显高于所研究烃源岩,这与生物标志化合物成熟度参数的结果相吻合。依据甲基单金刚烷指数MAI和甲基双金刚烷指数MDI与镜质体反射率间的对应关系,发现该凝析油对应的镜质体反射率RO值介于1.3%-1.6%之间,由此说明它源于盐城凹陷内处于凝析油气阶段的泰州组烃源岩。由此可见,金刚烷类化合物在确定原油和烃源岩中有机质成熟度上具有特殊意义。

The saturation fractions were analyzed by GC-MS from the condensate （E1f1） and the source rock （K2t2） in well Yancan 1 in the Zhujiadun Gas Reservoir of the Yancheng Sag. The results show that they have similar distributions and compositions in steranes and hopanes,which suggests that this condensate is related to the K2t2 source rocks. However, the maturity of the condensate is higher than that of the source rock based on Ts/Tm and C29 sterane 20S/（20S＋20R） ratios. Diamondoid hydrocarbons are a kind of thermally more stable hydrocarbons in crude oils and source rocks,and alkyl diamantanes are thermally more stable than alkyl adamantanes. In the condensate, alkyl adamantanes and diamantanes were relatively abundant. However,alkyl adamantanes were only identified,and alkyl diamantanes were not whole or even absent in the K2t2 source rock. This phenomenon indicates that the condensate has higher maturity compared with the source rock, consistent with biomarker compounds. Based on the relationship between methyl adamantane index MAI, methyl diamantane index MDI and the vitrinite reflectance Ro values, the Ro value of the condensate is up to about 1.3 %-1.6 %,indicating that it was derived from the deeper K2t2 source rocks in the Yancheng Sag and diamondoid hydrocarbons have a specific role in the determination of thermal evolution of organic matter.