PREDICTION OF FRACTURE ROUGHNESS AND OTHER HYDRAULIC PROPERTIES FROM HRXCT

Open, connected fractures dominate fluid flow and solute transport where present. A challenge in predicting flow and transport in fractured media is describing representative physical characteristics appropriate to modeling. Fracture aperture, roughness, and channeling characteristics are important to predict flow and transport in hard rock terrains. Upscaling from hand or core sample properties would be highly beneficial but must assume a scale invariant or smoothly transformable relationship between fracture morphology and discharge. We analyze results of flow tests and flow modeling through natural fractures imaged by computed tomography. Using an areal roughness metric, statistics of roughness are plotted against sample size. For fracture specimens measuring up to 725 cm², a 10 cm² sample yields a representative roughness, but apertures cannot be scaled from this size. Our data indicate that hydraulic aperture cannot be predicted by single aperture measurements or averaging along scan lines but is best approximated by a geometric mean aperture.