针对乌石凹陷生烃特征不清和不同层系油气成藏差异性问题,通过烃源岩评价、生烃史演化分析、油源精细对比等手段对其烃源岩生烃特征及其差异成藏模式展开了研究。研究结果表明,乌石凹陷存在流二段上部和下部2套烃源岩,为形成于还原环境的中深湖沉积油页岩和泥页岩,富含无定形有机质和非海相沟鞭藻等藻类,以Ⅰ型和Ⅱ1型干酪根为主,为好-优质烃源岩。生烃动力学及生烃演化史分析显示,Ⅰ型干酪根生油能力最高,Ⅱ1型干酪根具有较高的生油能力,烃源岩存在2期生烃高峰期,第一期生烃高峰为涠洲组沉积末期(约23 Ma),第二期为角尾组沉积末期(约10 Ma),对应2期生烃高峰都伴生明显的生烃增压过程,是造成近洼带流二段普遍发育异常高压的原因。油源精细对比分析表明,中浅层涠洲组、流一段原油来自于流二段上部烃源岩,主要赋存于近洼带;流二段、流三段原油来自于流二段下部烃源岩,主要赋存于远洼带。综合研究认为,乌石凹陷表现为近洼带源外中浅层富集、远洼带源内富集的油气差异成藏规律。研究成果对于该区优化勘探、进一步扩大勘探成果具有重要指导意义。
There are two hydrocarbon source rocks in Wushi Sag, mainly distributed in the main depression of the middle area and the east depression.This paper studies the characteristics of the hydrocarbon source rocks and the differential reserve modle by hydrocarbon evaluation, their generation evolution and the comparison of their sources. The results indicate that the two sets of source rocks are actually oil shale and mud shale of middle-deep lake deposition, formed in reducing environment. The rcoks contain rich palynomorph organic matter and non-marine dinoflagellate fossils and dominated by typeⅠ and typeⅡ1 kerogen, showing they are good to high-quality hydrocarbon source rocks. The generation kinetics analysis shows that type I kerogen has the highest oil generation capacity, followed by type Ⅱ2 kerogen. The evolution history of hydrocarbon expulsion analysis suggests that hydrocarbon source rocks in this area have two students peak periods of hydrocarbon, the first students hydrocarbon peak, about 23 Ma, and the second peak, about 10 Ma, corresponding to the two students peaks of hydrocarbon associated with obvious hydrocarbon generation pressurization process. The measured formation pressure data reveal nearly depression belt of the abnormal high pressure is widespread in the second member of Liushagang Formation. Detailed oil source correlation analysis of major oil and gas rich areas in Wushi Sag shows that the crude oil in WZ and L1 from the top source rocks of the second member of Liushagang Formation, is mainly enriched in the near depression zone, while the the crude oil in L2 and L3 from the bottom source rocks of the second member of Liushagang Formation is mainly reserved in the remote belt. Comprehensive study shows that the Wushi Sag is characterized by medium-shallow accumulation in the near-sag zone and medium-deep accumulation zone in the far sag. The research results have important guiding significance for optimizing exploration in this area and further expanding the exploration results.
Geological Science and Technology Information
hydrocarbon source rock