Lithofacies characteristics and impact on pore structure of the Shahezi Formation shale, Changling Fault Depression, Songliao Basin

A lithofacies classification was established based on TOC and XRD data on cores of the Shahezi Formation in the Changling Fault Depression of the Songliao Basin. There are 7 lithofacies in the study area. Scanning electron microscopy, CO₂ and N₂ adsorption and high pressure mercury intrusion experiments were applied to quantitatively characterize pore structure. Shale pores were developed in the Shahezi Formation, and the pore types of different lithofacies were also different. Organic matter pores were mainly developed in argillaceous shale. Shale pore size exhibited a multi-peak distribution. Mesopores were the main contributors to pore volume, accounting for an average of 50.9%. Micropores were the main contributors to specific surface area, accounting for an average of 67.8%. The development of micropores was mainly controlled by clay minerals, the development of mesopores was controlled by carbonate minerals, while the development of macropores was controlled by the combination of siliceous and clay minerals. The organic-rich argillaceous rock influenced the surface area and pore volume, and played a major role in controlling shale pore development of the Shahezi Formation.