Rock fracture aperture and gas conductivity measurements in situ

Abstract

Recent interest in locating a nuclear waste repository in unsaturated fractured rock has lead to rock characterization studies. Essential to a study of this type is the measurement of natural rock fracture apertures and gas conductivities. Six pneumatic connections located in unsaturated crystalline rock were tested using gas flow tests conducted in parallel boreholes. It was believed, but not possible to verify accurately enough given the limited orientation data, that the pneumatic connections represented individual fractures. For the purpose of analysis, it was assumed that the pneumatic connections tested were "equivalent" to isolated individual fractures intersecting both test boreholes. Analytical equations were developed to treat fractures inclined to the borehole axis. These equations were used to calculate equivalent pneumatic apertures and equivalent gas conductivities from the test data. Equivalent pneumatic apertures calculated ranged from 9 to 200 microns and equivalent gas conductivities ranged from 3.78E-3 to 1.92 m/s.