Reservoir characteristics of Upper Permian Leping Formation shale in Pingle depression

On the basis of field geological investigation, old well reexamination and analysis results, the reservoir characteristics of Leping Formation shale in Pingle depression was discussed in such aspects as distribution characteristics, geochemical characteristics, mineral composition features and micro-pore features. The results show that Leping Formation shale is widely distributed and its thickness is above 100 m. The total organic carbon content of shale is high, reaching up to 0.21%-23.4%, averagely 1.74%, the thermal evolution degree of shale is also high, with Ro in the range of 0.7%-4.06%, averagely 1.88%, and the organic matter type is mainly of type II₂. The shale has abundant brittle minerals consisting mainly of quartz(averagely 47.94%)and shows a good fracturing potential; the clay minerals content is moderate(averagely 34.93%)composed mainly of illite and andreattite. The shale reservoirs have an average porosity of 3.5% and average permeability of 0.01×10^-3μm², implying a good physical property. The types of micropores include intergranular pores, intragranular pores and organic pores, as shown by scanning electron microscope. Shale reservoir pore shapes show opening state, including two-end opened cylindrical shape and four sides opened parallel pores. Further analyses show that the organic carbon content and quartz content were the major factor to control the shale reservoir porosity development, the effect of total organic content on shale micro-pores was mainly manifested in the development of micropores and mesopores, and the quartz mineral content contributed to macropores.