坳陷型富烃凹陷的主要特征和形成的动力学环境——以鄂尔多斯盆地为例

According to hydrocarbon exploration and existing studies all over the world, the heterogeneity of hydrocarbon distribution not only occurred among different basins, but also appeared just in the same basin, as the major reserves always centralized to a few hydrocarbon-rich sags rather than homogeneously scattered to all the sags in one basin. This phenomenon is especially behaved obviously in terrestrial petroliferous basins. While the existing studies in this aspect mainly focused on faulted basins. This application will take the well petroliferous middle-south part of the Ordos basin as a typical example of hydrocarbon-rich sag in depression-type basin. This study will focus on: 1) the sedimentary environment and geological features of the major high-quality source rock in Middle to Late Triassic Yanchang Formation; 2) the fundamental features of the tuff interlayer in the source rock, as well as its forming processes, distribution and its interaction with the high-quality source rock; 3) discussion on the regional tectonic events, paleo-geothermal field and its evolution, deep processes and coupling relationship with the neighboring Qinling orogen etc. Furthermore, the regional background and geodynamic setting will be discussed subsequently. Based on this study, several results are expected to gain, including: 1) creative thinking about geological condition and geodynamic setting contributed to formation of hydrocarbon-rich sags; 2) Taking breakthroughs at revealing the forming conditions, transformation processes and key controlling factors of the high-quality source rock; 3) more interpretation for hydrocarbon enrichment in the Ordos basin, as well as theoretical and scientific guidance for further exploration in this basin and similar areas.

国内外油气勘探和研究表明,不仅不同油区油气资源贫富悬殊,就是在同一含油气盆地,油气也主要来自盆内少数几个资源极为丰富的富烃凹陷。此特征在陆相盆地表现尤为明显。已有的相关研究大多集中在断陷类富烃凹陷。本项目以鄂尔多斯盆地中南部石油资源极为丰富的坳陷型富烃凹陷为重点解剖对象,研究该凹陷中晚三叠世延长期主力优质烃源岩发育期的地质特征和沉积环境,烃源岩中凝灰岩夹层和富铀特征的形成、分布和来源及其与优质烃源岩形成的关系,探讨烃源岩发育期间各种地质构造事件的发生和特征、古地温场演化、深部过程信息和盆山(秦岭)耦合-响应关系等,在此基础上探讨该富烃凹陷形成演化的动力学环境和区域构造背景。本项目研究可望在(1)富烃凹陷形成的地质条件和动力学环境方面取得创新成果;(2)揭示优质烃源岩形成和向烃类转化及其主控因素方面有突破进展;(3)为鄂尔多斯盆地石油资源丰富的形成原因和下一步勘探方向提供理论基础和科学依据。

项目以鄂尔多斯盆地南部中晚三叠世延长期富烃凹陷为重点解剖对象，通过大量野外地质考察、钻井岩心观察、测井和地震等资料和系列测试分析的综合研究,对延长期富烃凹陷的结构、沉积环境、物源特征，优质烃源岩展布、物质组成、地球化学特征，形成的主控因素及动力环境等开展了重点研究,揭示了延长组优质烃源岩与凝灰岩、铀异常、浊积岩及震积岩、深部热液活动等五位一体时空分布和叠合共存的关系, 探讨了富烃凹陷沉积-沉降中心叠覆和迁移的特征及规律，研究和总结了地面和覆盖区多种同沉积构造类型及其变形特征，首次提出了富烃凹陷和其中优质烃源岩形成期具构造活动明显、深部作用活跃的特征。通过对柴达木、江汉盆地和渤海湾盆地东濮凹陷、渤中凹陷咸化和断陷盆地富烃凹陷的对比研究，支持和佐证了此富烃凹陷形成构造环境的创新认识。.鄂尔多斯盆地南部富烃凹陷的形成，与同期秦岭地区南北大陆汇聚-碰撞和造山的演化过程时空响应、区域动力环境关联。据此和盆山对比研究，首次提出了此富烃凹陷属后陆盆地，具较热-伸展构造属性，是在大陆聚敛碰撞环境中仰冲板块一侧深部物质高度汇聚、能量转换，热物质上涌拱张所形成。.根据延长组烃源岩的个性特征,开展了系列不加和加铀、加代表火山灰的铬元素生烃热模拟对比实验和辐射生氢模拟实验,揭示出铀元素的参与可降低烃源岩生烃的温度域、增加生烃量；放射性辐射可促使不同流体产生烃源岩之外的外源氢；铬元素催化效应则与温度及有机质类型密切相关等。上述结果有助于全面、客观认识自然界烃源岩生烃的实际，发展和完善了油气生成和有机-无机相互作用理论；为探讨盆地石油资源丰富的成因提供了科学依据。.现已发表标注论文125篇（第1标注92篇，SCI收录28篇,EI收录27篇），出版专著2部，培养博、硕士研究生14名、34名;授权国家发明专利4项、获陕西省科技奖一等奖1项，圆满并超额完成了预定的任务和目标。