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<p>The Qiongzhusi Formation represents the second strata in China to achieve commercial shale gas development, following the Longmaxi Formation. However, a limited understanding persists regarding the pore structure of its shales, particularly concerning the distinctions between its shale and silty shale. This study comprehensively analyzed 25 samples of shale and silty shale from the Sichuan Basin. These analyses included total organic carbon content, X-ray diffraction, porosity measurements, field emission scanning electron microscopy, low-temperature CO<sub>2</sub> adsorption, low-pressure N<sub>2</sub> adsorption, and high-pressure mercury intrusion capillary pressure. Utilizing multifractal theory, the study investigated the pore structure differences between Qiongzhusi Formation shales and silty shales and their implications for shale gas storage and migration within the formation. The results indicated that the pore volume and specific surface area distribution trends for both shale and silty shale were generally consistent, with mesopores being the primary contributors to both pore volume and specific surface area. However, the shales exhibited superior characteristics, with pore volume of 0.0139 cm<sup>3</sup>/g and specific surface area of 10.305 m<sup>2</sup>/g, compared to silty shales, which showed pore volume of 0.0126 cm<sup>3</sup>/g and specific surface area of 8.184 m<sup>2</sup>/g. Moreover, the pore size distributions of both shale and silty shale displayed multifractal characteristics. In micropores and mesopores, the shales exhibited weaker heterogeneity in pore size distribution than the silty shales, while both possess higher correlation dimension (<i>D</i><sub>2</sub>) and Hurst exponent (<i>H</i>). Conversely, regarding macropores, the silty shales demonstrated weaker heterogeneity in pore size distribution compared to the shales, but the former’s <i>D</i><sub>2</sub> and <i>H</i> were higher than those of the latter. This suggests that micropores and mesopores in the shales are clustered and have better connectivity than those in the silty shales. Conversely, macropores in the silty shales are densely clustered and show better connectivity than those in the shales. Based on the analysis of pore structure, organic geochemical, and mineralogical characteristics, the shales demonstrated better gas-bearing potential. Therefore, shale gas exploration and development in the Qiongzhusi Formation should prioritize shale reservoirs.</p>

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Pore Structure and Multifractal Characterization of Shale and Silty Shale: Differences, Genesis, and Geological Implications from the Qiongzhusi Formation, Sichuan Basin

  • 期刊论文

  • 发表日期：

    2026年1月8日

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  • Huan Miao,
  • Zhenxue Jiang,
  • Jianchen Wu,
  • Wei Wu,
  • Qiuzi Wu,
  • Tian He,
  • Dandan Wang

摘要

The Qiongzhusi Formation represents the second strata in China to achieve commercial shale gas development, following the Longmaxi Formation. However, a limited understanding persists regarding the pore structure of its shales, particularly concerning the distinctions between its shale and silty shale. This study comprehensively analyzed 25 samples of shale and silty shale from the Sichuan Basin. These analyses included total organic carbon content, X-ray diffraction, porosity measurements, field emission scanning electron microscopy, low-temperature CO2 adsorption, low-pressure N2 adsorption, and high-pressure mercury intrusion capillary pressure. Utilizing multifractal theory, the study investigated the pore structure differences between Qiongzhusi Formation shales and silty shales and their implications for shale gas storage and migration within the formation. The results indicated that the pore volume and specific surface area distribution trends for both shale and silty shale were generally consistent, with mesopores being the primary contributors to both pore volume and specific surface area. However, the shales exhibited superior characteristics, with pore volume of 0.0139 cm3/g and specific surface area of 10.305 m2/g, compared to silty shales, which showed pore volume of 0.0126 cm3/g and specific surface area of 8.184 m2/g. Moreover, the pore size distributions of both shale and silty shale displayed multifractal characteristics. In micropores and mesopores, the shales exhibited weaker heterogeneity in pore size distribution than the silty shales, while both possess higher correlation dimension (D2) and Hurst exponent (H). Conversely, regarding macropores, the silty shales demonstrated weaker heterogeneity in pore size distribution compared to the shales, but the former’s D2 and H were higher than those of the latter. This suggests that micropores and mesopores in the shales are clustered and have better connectivity than those in the silty shales. Conversely, macropores in the silty shales are densely clustered and show better connectivity than those in the shales. Based on the analysis of pore structure, organic geochemical, and mineralogical characteristics, the shales demonstrated better gas-bearing potential. Therefore, shale gas exploration and development in the Qiongzhusi Formation should prioritize shale reservoirs.