Full-Scale Pore Structure and Fractal Characteristics of Continental Organic-Rich Shale: A Case Study of the Dongyuemiao Member of Jurassic Ziliujing Formation in the Fuxing Area, Eastern Sichuan Basin

Strong heterogeneity and complexity of continental shalesleadto significant differences in pore microstructure and fractal characteristics.In this study, the pore structure and fractal characteristics withina full-scale spectrum of continental shale from the Dongyuemiao (DYM)Member are systemically investigated using field emission scanningelectron microscopy (FE-SEM), gas adsorption, and high-pressure mercuryintrusion. Additionally, factors affecting the pore structure andfractal characteristics of Jurassic continental shale are discussed.The results show that, owing to the influence of mineral compositionand total organic carbon (TOC) content, the pore structure characteristicsof different shale lithofacies vary significantly. Argillaceous andmixed shales mainly develop interparticle pores, interlayer pores,or microfractures, and the pore volume (PV) is dominated by mesopores.Calcareous shale mostly develops dissolved macropores. The mixed shaleshave more complicated pore structures and stronger pore heterogeneity,as indicated by their larger fractal dimension (D) values. Significant positive correlations occur between the quartzcontent and PV, special surface area, and D value,while carbonate minerals show an opposite correlation trend. Positiverelationships exist between the clay minerals and the PV of micropores,whereas negative correlations exist between the average pore sizewith quartz, clay minerals, and D values. Shaleswith higher quartz and clay content have larger specific surface area(SSA), PV and smaller pore sizes, resulting in more complex pore structuresand stronger heterogeneity. Additionally, the TOC content is negativelyassociated with the total PV, D1, and D2, which is related to the limited organic matter (OM) pores developedin the DYM shale. Moreover, the presence of extracted OM reduces theroughness and complexity of micropores. The research results arehelpful to better understand the formation and evaluation of the complexpore system of Jurassic continental shale in the Sichuan Basin, andcan effectively guide the development of continental shale oil andgas resources in China.