Laboratory measurement of capillary pressure-saturation relationships in natural rock fractures

The focus of this work is on laboratory measurement of capillary pressure-saturation relationships in natural rough-walled rock fractures and on fracture aperture distributions. A laboratory technique was developed to measure capillary pressure curves for rough-walled fractures under different states of normal stress. Apparent aperture distributions, derived from the measured capillary pressure curves are compared to hydraulic apertures measured at the same normal stresses. The change in the aperture distribution with stress on one single fracture was studied without disturbing or opening the fracture.;The measured capillary pressure curves were found to be well represented with a Brooks-Corey porous media capillary pressure function. A distinct entry pressure, giving rise to initial non-wetting phase invasion, was observed in each test. The measured hydraulic apertures were found to be between the geometric and arithmetic mean apertures derived from the measured capillary pressure curves. The aperture distributions derived from the experiments were skewed to the smaller apertures and were well represented by a third asymptotic distribution of extremes. The apparent aperture distributions became less skewed at the higher stress level indicating larger percentages of medium and small aperture regions and smaller percentages of large aperture regions with increased stress. (Abstract shortened by UMI.)...