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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

Fractal dimension and its control factors of shales in Wufeng and Longmaxi Formations, Southwestern Sichuan Basin

Xiaolin Zhou, Yu Liu, Jian Wang, Zhengjiang Wang, Guoqing Xiong, Xiaohui Xiong, Yexin Zhou
Geochemical Journal, Vol. 54, No. , P. 299-314, 2020

ABSTRACT

In recent years, the Wufeng and Longmaxi Formations were identified as the favorable shale gas horizons. In order to further investigate the pore system and its controlling factor(s) in marine shales, twenty outcrop samples were collected from southwest of the Sichuan basin. The TOC content and mineral compositions were examined via geochemical analysis and the pore parameters were determined by the combined low-pressure nitrogen and carbon dioxide adsorption experiments. In addition, the fractal dimensions were calculated by the adsorption data. Our results show that the organic matter is the most significant factor controlling the development of nanoscale-pore in shales. The impacts of mineral compositions on pore system can be negligible. The poor correlations between fractal dimensions and TOC content and mineral compositions suggest that the fractal dimensions are not decided by the “relative content” of different shales components. The different correlations between fractal dimensions and average pore size and other pore parameters imply that the fractal dimensions are determined by the development of pores with different scales in shales. Particularly, the micro- and mesopore have opposite effects on the fractal dimensions. Based on the comparison of fractal dimensions observed in Wufeng and Logmaxi Formations, we suggest that the Longmaxi Formation has greater potential of exploration and development for the shale gas resource.

KEYWORDS

Wufeng-Longmaxi Formation, N2-CO2 adsorption, pore structure, fractal dimension, percentages of micropore and mesopore volumes

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