Multiscale evaluation of nanopore architecture and fractal geometry in shale reservoirs

Abstract Understanding the complex pore architecture of shale reservoirs remains a key challenge for accurate assessment of gas storage and transport behavior. A comprehensive investigation was conducted to quantify the nanopore architecture and fractal characteristics in shale formations from both the marine and continental depositional environments. A combination of X-ray diffraction (XRD), low-pressure nitrogen and carbon-dioxide adsorption (LP-N 2 A/-CO 2 A), and scanning electron microscope (SEM) were employed to investigate mineral composition, pore geometry, specific surface area, pore volume, and heterogeneity across micro- to macro-scales. SEM imaging revealed pronounced variability in pore morphology and heterogeneity, with fractal dimensions highly dependent on magnification and imaging location. These results highlight the importance of multi-scale imaging for representative quantification of shale pore networks. Gas adsorption results showed that microporous specific surface area (SSA) and pore volume (PV) are positively correlated with total organic carbon (TOC), whereas meso-/macro- porous development is primarily influenced by clay mineral content. Pore size distribution (PSD) trends differ notably by depositional environment: marine shale samples exhibit unimodal PSDs, while the continental sample displays a bimodal pattern. Fractal dimensions derived from Frenkel–Halsey–Hill (FHH) analysis of LP-N₂A isotherms ( D ₂ = 2.61–2.89) indicate varying degrees of surface roughness and pore complexity. The combined application of adsorption analysis, imaging, and fractal theory offers a robust framework for characterizing pore systems and assessing storage capacity and transport potential in shale reservoirs.