Controls of Different Quartz Types on Pore Structure in Black Shales from the Neoproterozoic Datangpo Formation

The pore structure and heterogeneity of shale reservoirs are keys to unconventional resource exploration and development. While the black shale of the Datangpo Formation (Nanhua system) has been extensively studied regarding manganese mineralization and depositional environments, research on its pore structure remains limited. This study employs a comprehensive approach integrating mineralogy, LPCA, LTNA, SEM, and EDS in order to systematically analyze the pore structure characteristics of the study area and to investigate its governing factors. The results show that the Datangpo Formation shale is dominated by quartz and clay minerals. Among quartz types, SiO2-terrestrial exhibits the highest proportion, followed by SiO2-biogenic, while SiO2-(S-I) is least abundant. Analysis of pore structure parameters in the study area reveals that mesopores are the primary contributors to the pore volume (PV) and specific surface area (SSA), accounting for 96.34% and 70.07%, respectively. Fractal dimension (D) analysis shows that the micropore fractal dimension (DS) ranged from 2.098 to 2.381, low-pressure mesopore fractal dimension (DF1) from 2.549 to 2.634; and high-pressure mesopore fractal dimension (DF2) from 2.480 to 2.545. Correlation analysis of pore structure parameters indicates that increased contents of SiO2-terrestrial and SiO2-(S-I) lead to higher PV, SSA, and DS values in the study area. Conversely, an increased SiO2-biogenic content significantly reduces PV, SSA, and DS values. D exhibits a clear positive correlation with micropores, where increases in PV and SSA promote higher D values. Furthermore, elevated TOC and brittle mineral contents also enhance D, while clay minerals inhibit DF1 and DF2.