物源与沉积相对鄂尔多斯盆地北部上古生界天然气优质储层的控制

Provenance and depositional facies controlling on the Upper Paleozoic excellent natural gas-reservoir in northern Ordos basin,China

利用LA-ICP-MS锆石微区原位U-Pb定年方法,建立了鄂尔多斯盆地北部上古生界下石盒子组盒8段与山西组山1段砂岩碎屑锆石的年龄谱系,结合砂岩重矿物分析、显微镜下碎屑矿物的定量统计与阴极发光鉴定,通过与源区地层同位素年代学的对比,分析了研究区上古生界天然气储层的物源区和母岩的时代、性质。在大量岩心观察与沉积相研究的基础上,通过镜下对砂岩薄片中碎屑矿物、填隙物、孔隙类型及其含量的观察与定量统计,结合砂岩图像粒度、孔隙度、渗透率、毛细管压力测试,研究了各砂岩类型及其骨架矿物与胶结物的特征、孔隙类型、储集物性及平面分布规律。讨论了源区母岩的性质、沉积相及空间展布、沉积作用与水动力条件等对形成天然气优质储层及储层储集性能演化的影响。

The age spectrum of detrital zircons in the He 8 and Shan 1 sandstones of the Upper Paleozoic from Ordos basin is constructed, and provenance and parent rocks for the Upper Paleozoic natural gas-reservoir in Ordos basin is studied in the first time, using LA-ICP-MS techniques of in situ U-Pb dating, accompanied with heavy and detrital mineral analysis and detrital mineral cathodoluminescence measurement, as well as comparative study of isotopic chronology of the parent rocks in provenance. Types of sandstones, detrital minerals and cements, pore types and reservoir quality of the different three sandstone types and their horizontal distribution characteristics are elucidated in this study, based upon robust core observation and description and depositional facies investigation, identification and quantitative statistics from sandstone thin sections under microscope, analysis of grain size, porosity and permeability, and capillary pressure measurement. Furthermore, provenance and parent rock chronology, impact of parent rock features, depositional facies, sedimentation and hydrodynamic condition on formation of excellent gas-reservoir and on reservoir quality evolution is also discussed in the paper. This study may answer to problem of provenance and parent rocks for the Upper Paleozoic, and understand controlling parameters for formation and evolution of excellent gas-reservoirs in Ordos basin. It is important to thoroughly examine deposition and tectonic evolution in northern part of the Ordos basin, and to predict prospect natural gas-rich area and promote exploration and development for hydrocarbon resources in the Ordos basin.