鄂尔多斯盆地延长期湖盆充填类型与优质烃源岩的发育

摘要

Lake-basin filling types response to the basin structures and plaeoclimate and control the development of high quality hydrocarbon source rocks. Based on comprehensive analysis of the depositional environment of Chang91, Chang73 and Chang72-71 source rocks, the authors recommend a balanced-fill type for these source rocks. However, as the abundance of organic matter and the scale of resource of these source rocks are different, the further subdivision of the balanced-fill type is needed. It is subdivided into delta front-deep lake, purely deep lake and turbidites-deep lake sedimentary systems corresponding to Chang91, Chang73 and Chang72-71 source rocks respectively. A discussion on the forming setting of excellent hydrocarbon source rocks was made. The authors point out that the basin subsidence and the climate controlled the sedimentation and preservation of source rocks, and the primary productivity was closely related to the surrounding volcanic activity and deep fluids. Integrating the relationship of basin and mountain, lake-basin filling types and lithofacies assemblage, the authors provide an ideal model for the development of Chang73 excellent hydrocarbon source rocks. This study emphasizes that the strong dynamic of water (such as turbidity current or delta) might have diluted the basin and embarrassed the enrichment of organic matter, whereas the nutrition elements from volcanic ash or deep fluid might have enhanced the production of organic matter. This understanding gives an example for further study of lake-basin filling types and development of high quality hydrocarbon source rocks in similar continental depression basins.%湖盆充填类型是盆地构造及古气候的综合反映，对优质烃源岩的发育有重要控制作用。在综合分析延长组优质烃源岩沉积环境的基础上，认为长91、长73、长72-长71烃源岩发育期湖盆都表现为平衡充填类型，但有机质丰度及规模有较大差别，因此进一步细分长91期为平衡充填三角洲前缘-深湖相组合沉积体系，长73期为平衡充填深湖相沉积体系，长72-长71期为平衡充填浊流-深湖相组合沉积体系，并指出长73期湖盆充填类型发育最优质烃源岩，进而重点探讨了其形成环境。本文认为盆地沉降过程与古气候变化主要控制优质烃源岩的沉积和保存条件，而湖盆原始生产力则与火山灰沉积和深部流体关系密切。综合长73期盆山耦合关系、湖盆充填类型、沉积岩相组合等，指出强水动力体系(浊流沉积、三角洲)对有机质起稀释作用，重点强调了火山灰沉积和深部流体带来的营养物质有利于提高湖盆原始生产力，进而初步揭示了长73优质烃源岩的发育模式。这一认识为进一步研究陆相坳陷湖盆优质烃源岩的充填类型及发育规律提供了可借鉴的研究实例。