Research on Sedimentary Reservoir Characteristics and Development Practice of Chang 8 Oil Layer Middle Section of the Western Edge of the Ordos Basin

In recent years, new breakthroughs have been made in the exploration and evaluation of the Yanchang 8 formation in the middle part of the western margin of the Ordos Basin, and a number of Wells have been tested to obtain high production, which has become a real development resource of the basin. However, the understanding of the Chang-8 series in the new area of the western margin is still weak, and the sedimentary and reservoir characteristics are not systematically studied. In this paper, the deposition and reservoir characteristics of Chang 8 strata in new area are studied in detail by means of outcrop, drilling core, cast thin section, conventional thin section, X-ray diffraction, scanning electron microscope and mercury injection. The results show that a multi-stage braided river delta plain superimposed sedimentary system is developed in the middle part of the western margin of the Ordos Basin, with large sand bodies in the west and thinning from west to east. The reservoir space is dominated by intergranular pores, and the pore types are mostly combination, mainly developed intergranular pores and feldspar dissolved pores, with an average porosity of 11.28% and an average permeability of 6.16 × 10−3 μm2, belonging to ultra-low porosity and ultra-low permeability reservoirs. Compared with the old area in the east, the physical characteristics of Chang 8 reservoir in the new area are coarse grain size, poor sorting and good porosity and permeability. It is mainly controlled by sedimentary environment, diagenesis and other factors, and the content of interstitial and clastic components is rich and different from the old area. The high development degree of chlorite protects the pores well in the early diagenesis. Less kaolinite content reduces pore plugging. A comprehensive study has been carried out on the fine development of layers and the optimization of key parameters of reservoir reconstruction, and good results have been achieved in the development practice.