【作者】 邱欣卫；

【导师】 刘池阳；

【作者基本信息】 西北大学 ， 构造地质学， 2008， 硕士

【摘要】 鄂尔多斯盆地延长组烃源岩中存在明显的放射性异常现象,结合国家973项目所取得的部分研究成果发现,这种异常主要由放射性铀元素引起。延长组凝灰岩与富铀烃源岩互层产出,在测井曲线上独特的表现为低电位、高伽玛、高声波时差和高电阻率值,人们以往关注的多,而深入研究的少,过去仅把这些夹层作为地层划分对比的标志层,一直未对其开展深入的岩石学和地球化学研究工作,对这些凝灰岩的成因的认识尚没有科学的数据和结论。所有的研究工作都未将延长组中铀元素的迁移和这些凝灰岩相联系,因此探索延长组富铀烃源岩的形成与凝灰岩夹层和铀异常之间的关系,为探讨凝灰岩的成因类型及其在烃源岩演化中所起的作用,具有重要的理论和实践意义。在深入分析前人研究成果的基础上,综合应用薄片鉴定、扫描电镜及能谱分析、X射线衍射分析、元素地球化学分析、铅和氧同位素分析等多项现代分析测试技术,详细研究了凝灰岩夹层的岩石学、地球化学特征,探讨了其属性,并分析了凝灰岩中铀元素的迁移特征;通过多次野外考察和细致的岩芯观察,结合测井资料,调查了凝灰岩发育井位及层位,分析了其展布规律,揭示了其形成环境,阐述了凝灰岩与烃源岩二者之间的关系等科学问题。论文首次把传统意义上的延长组凝灰岩分成凝灰岩、斑脱岩、热水沉积岩三类,并且认为凝灰岩和斑脱岩包含有空降型和水携型两种成因机制;分析了凝灰岩中铀元素近代发生过丢失迁移现象,很可能是富铀烃源岩中铀元素的母岩;绘制了凝灰岩夹层单井、联井剖面图和长7₃底凝灰岩平面展布图。综合对比发现延长组凝灰岩夹层与盆地内同期烃源岩和放射性异常展布基本一致,相互之间可能存在联系;凝灰岩夹层的形成环境主要为浊积扇和深湖环境,浊积岩中的凝灰岩蚀变后使其储层各项指标发生变化,而深湖相中的凝灰岩可能是沉积环境从氧化向还原过渡的有利因素,同时利用地球化学数据判别出凝灰岩可能来自于火山弧或板内、钙碱性岩浆环境。综合分析认为,凝灰岩夹层不仅是地层划分的标志层。也是有机—无机相互作用的重要纽带,对生油层和储集层具有重要的石油地质意义,同时也可能是促使鄂尔多斯盆地原油品质较好的重要因素。更多还原

【Abstract】 There is remarkable radioactive abnormal phenomenon in the source rocks of Yanchang formation in Ordos. It has been found that the anomaly mainly caused by radioactive uranium element, combined with partial research achievements of the National Important Basic Research Program. The tuffs and the rich uranium hydrocarbon source rocks interbed output, with the unique characteristics of low SP, high Ga, high AC and high Resistivity value in well logging curves. People pay much attention, but deeply research few on tuffs, just regarded which as stratum division and contrast marker beds, and without thorough petrology and geochemistry research work, there are not science data and conclusions to understand the tuffs’ genesis yet. And all past research work had not discussed the relationship between uranium element migration and tuffs. So exploring the formational mechanism of rich uranium hydrocarbon source rocks, explaining the relationships between tuff interlayer and uranium abnormality of Yanchang formation, it has important theory and practice significance, for discussing tuffs’ genetic types and the role which plays in hydrocarbon source rocks mature process.Based on the analysis of predecessor research thoroughly, with the help of synthesis using many modern analysis and test technologies, including thin slice identification, scanning electron microscope and energy spectrum analysis, X-ray diffraction analysis, elements geochemistry analysis, Lead and Oxygen isotopes analysis and so on, the petrology and geochemistry characteristics of tuff interlayer has been particular researched and discussed its attribute, the uranium element migration characteristic in the tuff has been analyzed. Through several outfield work and careful rock cores observation, combining well log data, then investigated the position of well and layer about tuffs, and the relationship between the tuffs and hydrocarbon source rocks, the distribution rule and formation environment, as well as some scientific questions had been discussed.It is divided the traditional tuffs into three types which in Yanchang formation: ash tuffs, bentonites and hot water sedimentary rocks, the formational mechanisms of tuffs and bentonites containing fall down and water-carrying. Proved the phenomena of uranium element loss and transport in tuffs in modern time, and the tuffs maybe were the source rocks of uranium element in the rich uranium hydrocarbon source rocks. At the same time, the single well and the associated wells sections of tuffs interlayer and the Chang 7₃ bottom tuffs’ plane had been done. The synthesis contrast had shown that the distribution of tuffs interlayer, the hydrocarbon source rocks and the radioactive abnormal was basic consistent in Yanchang formation. So it has the inevitable relationship. The tuffs’ formational environments mainly are turbidity fan and deep lacustrine facies. The altered tuffs in turbidity fan maybe influence reservoir indexes, and tuffs in deep lacustrine facies maybe were the favorable factor on the transition from oxidation to reduction environment. Meanwhile, tuffs was distinguished maybe were from the volcano arc or within plate and calc-alkaline lavas through geochemistry data.Synthesis analysis believed that the tuff interlayer was not only the stratum division contrast horizon marker bed, but also was the important belt of organic-inorganic interaction, it had the important petroleum geology significance for source rocks layer and the reservoir, at the same time, it maybe was the important factor on improving the crude oil quality in Ordos basin.更多还原