Multiscale Characterization of Pore Structure and Heterogeneity in Deep Marine Qiongzhusi Shales from Southern Basin, China

The pore structure of shale is a critical factor influencing the occurrence and flow of shale gas. Characterizing the pore structure and studying its heterogeneity are of paramount importance for a deeper understanding of the laws governing hydrocarbon occurrence, as well as for enhancing the efficiency of exploration and development. This work addresses the complex characteristics of multiscale coupling in the pore systems of shale reservoirs, focusing on the ultra-deep Qiongzhusi Formation shale in the southern region. Through the integrated application of cross-scale observation techniques and physicochemical analysis methods, a refined analysis of the pore structure is achieved. Utilizing field emission scanning electron microscopy imaging technology, the types and morphological characteristics of pores are identified. Additionally, a fluid–solid coupling analysis method employing high-pressure mercury intrusion and low-temperature gas adsorption (CO2/N2) is utilized to elucidate the characteristics of pore structure and heterogeneity while also analyzing the influence of matrix components on these features. The results indicate that the shale of the Qiongzhusi Formation is rich in feldspar minerals, facilitating the development of numerous dissolution pores, with the pore system predominantly consisting of inorganic mineral pores. The full pore size curve of the shale generally exhibits a bimodal characteristic, with a high proportion of mesopores. A strong positive linear relationship is observed between pore volume and specific surface area, whereby larger pore spaces reduce pore heterogeneity, with mesopore volume playing a decisive role. This study provides scientific support for the evaluation and strategic deployment of exploration and development in ultra-deep shale reservoirs of the Qiongzhusi Formation.