High Resolution Cat Imaging of Fractures in Consolidated Materials

High resolution measurements of fracture aperture of granite and sandstone rocks were performed using CAT scanner. The aperture distribution was statistically characterized for future experimental and numerical studies on single and multiphase flow and transport. The fracture aperture can be measured in-situ and nondestructively with CAT-scanning. The minimum pixel size is 0.27 x 0.27 mm, but fractures as small as 35 μm can be accurately measured, using a calibration standard for the variation in CT number due to the “missing rock mass” in a given pixel. A calibration standard for each rock type yields distinctly different calibration slopes, about 17% greater for granite compared to sandstone, indicating that each rock type should be analyzed against its own calibration standard. The aperture distribution is rather heterogeneous and is best described by a lognormal function, corroborated by comparing the theoretical to actual ratio of hydraulic to mechanical apertures. Mechanical roughness of the fractures ranged from 0.17 to 1.5. The variability in fracture aperture displayed only short range structure, with correlation lengths of 0.8 mm to 7 mm, which is at most one-tenth of the minimum dimension (width) of the fracture plane. Potential flow channels can be deduced from the fracture aperture distribution.