Quantitative Characterization of Shale Pore Structure Based on Ar-SEM and PCAS

Shale pore characteristics are important part of shale reservoir research. Based on the shale samples from Taiyuan Formation and Shanxi Formation in the S-1 well of Qinshui basin, the morphology of the pores was analyzed by argon ion polishing scanning electron microscope (Ar-SEM), and the pores of the Ar-SEM micrographs were quantitatively characterized by pores and cracks analysis system (PCAS). The results show that the pore types of the samples are mainly organic matter pores, intergranular pores, and intragranular pores. The pore sizes are mostly less than 100 nm, accounting for 72.70%-82.13%, and the mesopore ratios are 39.76%-45.48%, which is favorable for pore connectivity and gas migration. The pore structure becomes increasingly more complex with the increase of depth; but the deeper the layer, the more slowly the structural complexity increases with the increase of pore area.There is an inflection point in the vicinity of R_{o, max}=2 for the pore structure complexity. In the high maturity stage, the complexity of the pore structure gets increasingly lower with the increase of the maturity, and the structure complexity is lower as the pore area is larger; in the over mature stage, pore structure is increasingly more complex with the increase of maturity, and the larger the pore area, the greater the structural complexity.