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

Abstract

Strong heterogeneity and complexity of continental shales lead to significant differences in pore microstructure and fractal characteristics. In this study, the pore structure and fractal characteristics within a full-scale spectrum of continental shale from the Dongyuemiao (DYM) Member are systemically investigated using field emission scanning electron microscopy (FE-SEM), gas adsorption, and high-pressure mercury intrusion. Additionally, factors affecting the pore structure and fractal characteristics of Jurassic continental shale are discussed. The results show that, owing to the influence of mineral composition and total organic carbon (TOC) content, the pore structure characteristics of different shale lithofacies vary significantly. Argillaceous and mixed 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 shales have more complicated pore structures and stronger pore heterogeneity, as indicated by their larger fractal dimension (D) values. Significant positive correlations occur between the quartz content and PV, special surface area, and D value, while carbonate minerals show an opposite correlation trend. Positive relationships exist between the clay minerals and the PV of micropores, whereas negative correlations exist between the average pore size with quartz, clay minerals, and D values. Shales with higher quartz and clay content have larger specific surface area (SSA), PV and smaller pore sizes, resulting in more complex pore structures and stronger heterogeneity. Additionally, the TOC content is negatively associated with the total PV, D1, and D2, which is related to the limited organic matter (OM) pores developed in the DYM shale. Moreover, the presence of extracted OM reduces the roughness and complexity of micropores. The research results are helpful to better understand the formation and evaluation of the complex pore system of Jurassic continental shale in the Sichuan Basin, and can effectively guide the development of continental shale oil and gas resources in China.

Quantitative Characterization of Coal Shale Pores and Fractures Based on Combined High-Pressure Mercury Pressure and Low-Temperature N2/CO2 Adsorption Methods

“…Image analysis methods such as SEM, TEM, and FIB-SEM can be used to obtain fine pore structure images of coal rock, − and nonfluid injection methods such as nano-CT, NMR, small-angle neutron scattering, etc. can be used to quantitatively characterize the internal confined pore structure of the coal rock and the reservoir pore size, shape, orientation, and connectivity to a certain extent.…”