Pore-fracture evolution and seepage behavior in sandstone under triaxial stress: Insights from real-time CT imaging

Understanding the mechanisms of pore-fracture evolution and their effects on permeability is critical for predicting seepage behavior in fractured porous media. However, the real-time capture of these dynamic processes under realistic stress conditions remains technically challenging and has not been thoroughly explored. This study presents a methodology that integrates real-time CT scanning with 3D digital reconstruction and numerical simulation techniques, enabling the dynamic monitoring of structural evolution and fluid flow characteristics. Quantitative and morphological analyses were conducted on reconstructed models at different loading stages, and seepage simulations based on reconstructed pore-fracture structures were carried out to investigate fluid migration. Furthermore, a semi-logarithmic model linking permeability to fractal dimension was proposed and validated, providing a predictive tool based on microstructural characteristics. The analysis shows that shear-induced dilation causes isolated small pores to expand and form larger pores that eventually integrate into the connected network before cracking. After cracking, newly formed fractures promote the incorporation of isolated pores, whereas subsequent fracture closure leads to a reduction in the connected pore volume and an increase in the isolated voids. The fracture network forms a funnel-shaped pattern, extending from the specimen ends toward the center. Numerical simulations show that the evolution of the pore-fracture network significantly alters the seepage pathways and flow efficiency. Permeability exhibits a strong positive correlation with coordination number and throat size. These findings provide a new perspective on characterizing and predicting seepage behavior under realistic stress conditions, offering significant scientific and engineering implications for underground fluid control and hazard mitigation.