塔木察格盆地南贝尔凹陷西部次凹下白垩统沉积和石油地质特征

Sedimentary and Petroleum Geological Characters of Lower Cretaceous in West Sub-Sag, South Buir Sag of Tamtsag Basin

摘要: 蒙古国塔木察格盆地南贝尔凹陷西部次凹的发育主要受北东向同生正断层控制，叠加有基底地形起伏和北东东–近东西向剪切变换构造的影响。早白垩世早期为断陷阶段，相发育在西部次凹全区经历了统一–分异–再统一的完整旋回。铜钵庙组和南屯组主要发育扇三角洲相、近岸水下扇和湖泊相，扇体展布及其亚相发育受东、西两侧的物源区控制。西南侧的“临时性”物源区造成铜钵庙组沉积期南洼槽的沉降中心与沉积中心不一致。因厚度、岩性和岩相空间变化较大，源岩和储层发育因地而异。南洼槽烃源岩发育好，有机质以II2型为主，热演化经历了未成熟、成熟和生油高峰3个阶段。砂体发育在中–北洼槽较好，现有资料表明以特低孔–超低渗型储层为主。

Abstract: The evolution of the West Sub-Sag, South Buir Sag of Tamtsag Basin in Mongolia is mainly controlled by extension of the contemporaneous NE-orientated faults. In addition, it is superimposed with the influences of the base-mental relief and the transferring of NEE- /near WE-orientated shear fracture. The early Early Cretaceous was a fault-depressing stage of the West Sub-Sag’s tectono-sedimentary evolution, and the facies developing experienced a complete cycle of universal- differentiation-re-universal. In the Tongbomiao and Nantun Formations, the major sedimentary facies-types are fan delta, inshore underwater fan and lacustrine facies. The distribution of fan bodies and each sub-facies occurring of fan delta and inshore underwater fan should be constrained by the source regions to both the eastern and western sides. To the southwestern side of the South Hollow, there existed a “temporary” source region, which resulted in the subsidence center being not superposition with the depocenter during the sedimentary period of the Tongbomiao Formation. Owing to spatial changes of the thickness, lithology and petrofacies, the source rocks and reservoirs in the West Sub-Sag display distinct inhomogeneity. In the South Hollow, the source rocks are better occurred, with the organic materials being mainly II2-type. The organic thermal evolution can be divided into three stages: unmatured, matured and oil-generating peak stages. The sand bodies are better developed in the Central-North Hollow. The available data demonstrate the reservoir’s physical property being relatively poor, namely, the majority being reservoir with extra-lower porosity and super-lower permeability.