南黄海盆地中-新生界湖相烃源岩地球化学特征及生烃史

Geochemical characteristics and hydrocarbon generation history of Mesozoic-Cenozoic lacustrine source rocks in the South Yellow Sea Basin，offshore eastern China

李志强 杨波 王军 韩自军 吴庆勋

Zhiqiang Li Bo Yang Jun Wang Zijun Han Qingxun Wu

南黄海盆地迄今未获商业性油气突破，或与对其中-新生界3套湖相烃源岩的发育模式和生烃史研究薄弱有关。对来自3套烃源岩的41块样本进行岩石热解、微量元素、X衍射和色谱-质谱分析后发现，泰州组二段腐泥组含量高，为Ⅱ型干酪根，以水生有机质输入为主，C甾烷占优，受海侵影响碳酸盐矿物含量高，古水体还原性强且盐度高，利于有机质保存；阜宁组二段和泰州组二段古水体环境相似，但C甾烷含量显著增高，为藻类为主和陆源为辅的双重有机质输入，是典型的湖相烃源岩；阜四段的C甾烷含量占绝对优势，TAR比值高，为单一的陆源有机质输入，古水体偏氧化性且盐度低，不利于有机质的保存。烃源岩复杂的母质输入类型和沉积环境不利于对其热成熟度的评价，对以甾烷20/（20+20）或Ts/（Ts+Tm）参数表达的“未熟”特征应谨慎。基于断陷型-拗陷型的构造背景转换分析，建立了潜力生油层的生烃过程，认为活跃的火山活动对烃源岩生烃有促进作用，且北部坳陷以早期生烃为主，南部坳陷存在早、晚两期生烃，以三垛组沉积时期生烃为主。研究对南黄海盆地下一步的油气勘探部署具有重要指导意义。

No commercial oil or gas discovery has ever been made in the South Yellow Sea Basin （SYSB）， offshore eastern China so far. This is probably due to the lack of study on the development and hydrocarbon generation history of the three sets of Mesozoic-Cenozoic lacustrine source rocks in the basin. Rock pyrolysis， trace elements， X-ray diffraction and chromatography-mass spectrometry analyses on 41 samples collected from the source rocks show that the second member of the Taizhou Formation （K） （one of the three sets） is rich in sapropel of Type Ⅱ kerogen， mainly the result of aquatic organic matter （OM） input as indicated by a dominant C regular sterane. The member has high content of carbonate minerals， suggesting a transgression influence that caused an anoxic and saline paleoenvironment， favorable for OM preservation. The second member of Funing Formation （E） shares the paleoenvironment with K but has dramatically higher content of Cregular sterane and a dual OM input of dominant algae with a small amount of terrestrial material， suggesting typical lacustrine source rocks. The fourth member of Funing Formation （E） contains mostly C regular sterane and has high terrestrial /aquatic ratio （TAR）， indicating terrestrial OM input and oxic ancient water body with low salinity that is not favorable for OM preservation. The complex OM input mix and paleoenvironment conditions make it difficult to evaluate the thermal maturity of the source rocks. It is recommended to treat with caution the “immature” characteristic expressed by the ratios such as sterane 20/（20+20） or Ts/（Ts+Tm）. The hydrocarbon generation process of potential source beds is established base on analysis of structural background transformation from fault-depression period to depression period. It suggests that volcanic activities facilitated the generation process and that the depressions in the north experienced an early hydrocarbon generation and those in the south went through both early and late hydrocarbon generation but with a major generation period occurring during the deposition of the Sanduo Formation. The study may serve to guide the next step of oil and gas exploration in the basin..

10.11743/ogg20220214