Characteristics of Organic Matter Distribution in the Ordos Basin Western Margin Ordovician Wulalik Formation

Abstract Using the latest drilling and field outcrop data, the organic matter type, organic matter abundance, degree of thermal evolution of organic matter, and organic matter endowment state of low-TOC marine shale in the Ordos Basin’s western margin of the Ordovician Wulalik Formation are investigated, and Characterization of organic matter development and storage state of high-quality shale clarified. In this paper, detecting the total organic carbon(TOC) by combustion oxidation-non-dispersive infrared absorption, organic matter types were categorized by casein microscopic component identification, reflectance of specular plasmas ( Ro ) indicated the degree of thermal evolution of organic matter, and argon ion-polished field emission scanning electron microscopy (FEM-SEM) was used to observe the organic matter endowment status of shale samples. The organic carbon content of the shale of the Wulalik Formation at the western margin of the Ordos Basin ranges from 0.05% to 3.71%, the average is 0.54%. The organic matter type is type I sapropelic mud type, and the Ro ranges from 1.73% to 3.02%, the average is 1.88%, and the degree of thermal evolution has reached a high maturity stage; Organic matter in the shale of the Wulalik Formation in Zhongping 1 well is mainly endowed in clay mineral interlayer pores, white mica interlayer pores, brittle mineral intergranular pores, microfractures, semiautomorphic-automorphic pyrite microcrystalline interstices as well as in the form of graptolite residual epidermis, Collectively, they bolster the total organic carbon concentration within the Wulalik Formation. The organic geochemical parameters of different areas of the Ordovician Wulalik Formation at the western margin of the Ordos Basin are statistically summarized and analyzed, with a view to providing assistance to the exploration and geological research of marine shale gas in northern China in a sustained and in-depth manner.