洞庭盆地沅江凹陷的发育特征与含油气性研究

【作者】 郑华平；

【导师】 张廷山； 徐克定；

【作者基本信息】 西南石油大学 ， 矿产普查与勘探， 2006， 博士

【摘要】 沅江凹陷位居洞庭盆地之中，是其中的一个沉陷最深、地层发育最完整、沉积厚度最大、油气显示最丰富、资源前景最好的凹陷。该凹陷北与华容隆起相接，南邻雪峰隆起，东西分别与麻河口凸起和目平湖凸起相离连，呈北东向延伸，长约75千米，宽约33千米，是一个较典型的东南断西北超的中、新生代箕形凹陷。论文总的指导思想是以现代石油地质理论为基础，以整体、动态、系统、综合分析为原则，以成盆—成烃—成藏研究为主线，运用残留盆地油气成藏系统评价思路，从盆山耦合关系切入，研究含油气系统成藏要素及其相互作用过程，探讨油气成藏主控因素和油气分布的有序性，取得如下主要的创新性成果和认识： 1：系统分析了洞庭盆地形成演化与雪峰—幕阜构造带的关系，提出来了盆山之间一共经历了四期的盆山耦合过程：1) 燕山早中期的盆山耦合过程；2) 燕山晚期的盆山耦合；3) 早喜马拉雅期的盆山耦合；4) 晚第三纪的盆山耦合。 2：描述了沅江凹陷内的构造样式，认为凹陷内构造变形具有西南断、东北超的的箕状断陷特征，并将凹陷划分为三个一级构造带及九个二级构造带，并将其在各个盆山耦合过程中的具体构造演化特征划分为5个发展阶段：①中白垩世扭张性盆地发展阶段，②晚白垩世坳陷阶段，③古新世至始新世断陷盆地扩张阶段，④始新世中晚期断陷盆地收缩阶段，⑤晚第三纪至第四纪坳陷阶段等五个阶段。 3：对工区内的白垩系地层与第三系地层的界限的进行了确定，并根据钻井资料将沅一段自上而下可将其划分为彼此相间的四个辅助标致层（即Ⅰ-Ⅳ油层组），沅二段可划分为第三、四两个辅助电性标志，并确定沅一段、沅二段的分界线，以及对工区地层与邻区地层进行了对比。 4：沅江凹陷早第三纪经历了冲积扇、河流→湖泊（扇三角洲、三角洲、湖底扇）→河流的发育演化过程，反映了盆地从初期形成→扩张→萎缩的完整演化序列。早第三纪后期由于受到喜山期的褶皱抬升作用，使盆地沉积遭受严重剥蚀并日渐萎缩。并将其划分为两个Ⅲ级层序，层序Ⅲ₃（E₁t—E₂y）形成于盆地断—坳时期，层序Ⅲ₄（E₂h—E₂x）形成于盆地坳陷期。各层序充填阶段发育的沉积体系有相似之处，又各有特点。 5：通过对沅江凹陷的烃源岩的类型，分布发育规律的分析后，综合认为沅江凹陷的有利烃源层主要发育在半地堑的二个深洼部位，早第三纪沅江早期，是凹陷的主力烃源岩主要发育期，控制了烃源岩的分布、规模和质量。而储集层则主要发育在沉积层序顶部的高水位晚期和低水位早期，因此提出凹陷深洼处发育的扇三角洲及湖泊三角洲砂体，是油气的有利勘探区。 6：我们认为，沅江凹陷下第三系和白垩系油源均来自下第三系本身，在对其含油气系统的划分上，将其作为“一源多储”的三个相互叠置的含油气子系统对待：1) E₁t+E₂y¹—E₂y含油气子系统；2) E₁t+E₂y¹—K₃f含油气子系统；3) E₁t+E₂y¹—E₂h含油气子系统。上述三个含油气子系统虽然储集层各不相同，但是烃源层基本上是一样的。因此，更多还原

【Abstract】 Yuanjian depression which located in Dongting basin is one of the most deep, in seeking perfectly development of stratum, thickness of sediment and the most abundance of petroliferous characters . It is conterminous of the Huarong arch in the north and adjacent of Xuefeng mountain in the south, and in the east and west of the depression are Mahekou arch and Mupinghu arch. It is extend to along the direction of North-East, and its length is about 75Km while the width is almost 33 Km. And in this study , based on the main theories such as Plate tectonics, basin-mountion coupling development, organic origin of petroleum, sequence stratigraphy ,petroleum system along the main way of basin - source -petroliferous pool, the author focuses on the yuanjiang depression and the adjacent regional characteristic of tectonic evolvement; summarizes the relation of tectonic evolvement and the distribution of oil-gas in the depression; and the distributing disciplinarian of gas- oil. The main conclusions included:（1） The structure style、the feature of the tansmutation and formation between Dongting basin and Xuefeng-Mufu Orogenic belt are Synthetical analyzed, the author considers that there is extreme coupling between the Orogenic belt and basins in the diffirent periods from Meso to Cenozoic:1) The early and middle stage of Yansha （J3-K1-2）; 2) The late stage of Yanshan （K31 -2）; 3 ) The early stage of Himalayan movement （form the late periods from the late Cretaceous to the Paleogene ） ; 4 ) The late stage of Himalayan movement（Neogene-Quaternary.） .（2） According to the analysis of the structural style of Yuangjiang depression, the author points out the southwestern of depression has take on the shape of rupture while the bestow in northeastern part.The depression can be despart into three main tectonic unites and nine secondary tectonic unites, each Basin-mountion coupling development can be experienced in such phase: ①The formation of so-shear rift basin in the stage of middle Cretaceous. ②The formation of subsidence basin in the stage of late Cretaceous.③ The stage of subsidence of fault blocks overspread between Paleocene and Oligocene. ④The middle-late stage of subsidence of fault blocks shrink in late Oligocene ⑤The stage of subsidence in the Neogene-Quaternary.（3） The boundaries between the strata from Cretaceous to Tertiary in Yuanjiang depression and the adjacent area have been divided and correlated.（4） In Eogene, with the formation to passing away of the rifts, their depositional environment showed regular diversification as foothill-fluvial-lake-fluvial （-foothill）, and almost all aqueous continental sediments were found here, and it reflected the perfect series of development of the yuanjiang depression.Two third class Sequence can be departed, it is Ⅲ₃ （E₁t - E₂y） .which developed in the period of fault subsidence-depression and Ⅲ₄（E₂h-E₂x）which develop the depression of the basin.（5） After analyzing the type and distributing discipline of sedimentary in Yuanjiang depression, the favorable source layer are located on the two deep low-lying area of Yuanjiang depression, main period of petroleum evolvement was Yuanjiang period of Eocene, and it control the distributing and size and quality of source. The Jingxiazhou fault block - fault anticline area are the most favorable petroleum gathered and preserved area where having the better combination of source、reservoir and cap-rock for that they are abut against the central of source of deep low-lying and the best place where developing the better reservoir such as sandstones and baiyun stones, and for another there been a lot of structual traps such as fault更多还原