The Da’anzhai Formation in the Sichuan Basin, as a typical continental shale sequence, exhibits favorable reservoir conditions with abundant shale oil and gas resources and significant potential, making it an important target for continental shale exploration and development in China. This study focuses on the continental shale of the Da’anzhai Formation in the central Sichuan Basin. Based on experimental methods such as X-ray diffraction, field emission scanning electron microscopy, low-temperature CO₂ and N₂ adsorption-desorption, and low-field nuclear magnetic resonance, a comparative study on the pore structure characteristics of different lithofacies was carried out. The main findings are as follows: (1) The Da’anzhai Formation can be classified into three major categories and six subcategories of lithofacies: silty clay-rich lithofacies, clay-silt mixed lithofacies, silt-shell limestone lithofacies, shell limestone-clay mixed lithofacies, clayey bioclastic limestone lithofacies, and bioclastic limestone lithofacies. (2) The primary storage spaces in the shale are dominated by intergranular pores between clay minerals, with a small number of organic pores and micro-fractures. The pore shapes are mainly sheet-like and slit-like. (3) Multi-method characterization indicates that the silty clay-rich lithofacies and clay-silt mixed lithofacies exhibit the most developed pore systems, while the bioclastic limestone lithofacies show the least development. This research systematically investigates the pore structure characteristics of the Da’anzhai Formation shale in the central Sichuan Basin using various methods and techniques, providing valuable insights for shale oil and gas exploration and development.
Li et al. (Thu,) studied this question.