| Relative permeability, a description of the ease with which any flow may pass through a system, can be described as an extension of Darcy's law for systems dominated by capillary frictions (Scheidegger 1974). In order to define relative permeability as a function of capillarity the key variables that control capillary pressures of a system that must be measured directly are the wetting properties of the phases, aperture geometry and pressure gradients within a system. Methods were developed to quantify the relationship between the pressure gradient across a fractured rock core as well as the position of an aqueous/NAPL fluid interface location in relation to aperture geometry. Magnetic Resonance (MR) imaging, which is capable of producing 3-dimensional images which characterize rock fracture geometry and two-phase fluid flow in fractured rock media (Becker 2003), is combined with the simultaneous collection of differential pressure data across the experimental rock fractures. Time-stamped MR imaging was used to view real-time multiphase fluid flows in fractured rock that allowed for the analyses of the interface location in relation to aperture geometry. Recorded capillary pressure data show that the pressure required to overcome smaller aperture geometries are directly related. Additionally, the data also suggest that local buoyancy forces in may also affect the mobilization of NAPL in rough-walled approximately horizontal rock fractures. |
