Characteristics of shale gas reservoir in Upper Paleozoic coal measures in Yangquan Block, Qinshui Basin

Shale reservoir characteristics are the basic content of shale gas storage capacity evaluation. In order to explore the properties of high-evolved coal-measures shale gas reservoirs and optimize favorable reservoirs, various experimental methods of rock pyrolysis, X-ray diffraction, scanning electron microscopy, high-pressure mercury intrusion, low-temperature N₂ and CO₂ gas adsorption were applied to the Qinshui Basin. Reservoir characteristics were studied with core samples of coal-measure shale core from the Upper Paleozoic in Yangquan Block. The results show that the Upper Paleozoic coal-measures shale in Yangquan Block of the Qinshui Basin has a high content of organic carbon(average TOC is 4.9%), is in an over-mature stage(average R_ran is 2.32%), and has a high content of clay minerals(average is 50.0%), with the characteristics of low porosity and low permeability(average porosity of 6.61%, average permeability of 0.006 3×10^–3 μm²). The pore types are mainly intergranular pores, intragranular pores and microcracks, and micro-nano-scale pores provide the storage space for the occurrence of shale gas; the total pore volume of pores is 0.025 5-0.051 7 mL/g, the average is 0.038 9 mL/g, the total specific surface area is 12.64-40.98 m²/g, the average is 28.43 m²/g, the pore volume of the micropores(< 2 nm), and the mesopores(2-50 nm) has a good positive correlation with the specific surface area, while the pore volume of macropores(>50 nm) has no obvious correlation with the specific surface area, indicating that the micropores and the mesopores are Yangquan blocks. The main carrier of coal-measure shale gas accumulation. In general, the Upper Paleozoic coal-measure shale in the Yangquan Block has good shale gas storage performance, but the shale reservoir has poor fracturing properties, which will affect the development of shale gas.