Numerical study on solute transport considering variable Péclet number and shear-induced aperture heterogeneity in rough-walled fractures

Le résumé fourni par la source

Shear displacement of natural fractures substantially reorganizes aperture structures and flow pathways, resulting in non-Fickian solute transport behaviors, for which the underlying mechanisms and quantitative representation in transport models remain incompletely understood. In this study, five rough-walled fracture configurations were reconstructed from a natural fracture surface subjected to different shear displacements. Direct numerical simulations of fluid flow and solute transport were performed under variable Péclet numbers (Pe) of 0.1–104. The breakthrough curves (BTCs) were analyzed using the classical advection–dispersion equation (ADE) and the time fractional advection–dispersion equation (tFADE). The results show that shear-induced aperture evolution increases aperture heterogeneity and reorganizes flow fields by enhancing preferential flow channels and promoting the formation of recirculation zones. These flow structures lead to pronounced early arrival and late-time tailing in BTCs under an advection-dominated transport regime. Compared with ADE, tFADE can better capture tailing behavior under advection-dominated conditions with relative error below 5% at the 99th percentile. The fractional derivative order α decreases with increasing aperture heterogeneity and exhibits strong negative correlations with flow-velocity variability and recirculation volume, with Pearson correlation coefficients of −0.937 and −0.850, respectively. Transport parameters in both ADE and tFADE exhibit systematic dependencies on relative standard deviation of aperture and Pe, enabling quantitative characterization of anomalous transport evolution in sheared fractures. These findings reveal the physical linkage between shear-induced geometric reorganization and non-Fickian solute transport in rough-walled fractures.

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