Fractal Characteristics and Pore Structures of Shales from the Doushantuo Formation, Yichang Area, South China

Low-pressure N2 adsorption experiments were conducted on 20 samples from the Doushantuo Formation in the Yichang area to quantitatively characterize their pore structures and fractal properties. The samples are mainly composed of quartz, dolomite, and clay minerals, with minor amounts of feldspar, calcite, and pyrite. The N2 adsorption–desorption isotherms display typical type IV characteristics with a pronounced hysteresis loop, indicating that mesopores are dominant. The specific surface areas range from 3.78 to 11.49 m2/g, and the total pore volumes range from 0.0039 to 0.0169 mL/g, with mesopores contributing most of the total pore volume. Fractal analysis based on the FHH model reveals two distinct fractal dimensions (Df): Df1 = 2.5–2.9 for small pores and Df2 = 2.0–2.3 for large pores. The fractal dimensions are negatively correlated with TOC, quartz, and carbonate contents but positively correlated with clay and pyrite contents. Higher organic matter content tends to produce relatively smooth organic pores, reducing pore heterogeneity, whereas higher clay content increases surface roughness and structural complexity. Overall, the heterogeneity of pore structures in the Doushantuo Formation shales is primarily controlled by mineral composition and organic matter content. These results provide new insights into the pore characteristics and storage potential of Ediacaran marine shales.