Abstract:
Fracture flow is fairly well documented with the widespread
application of, for instance, the cubic law and assumed smooth parallel plate model.
Geometrical intricacies such as aperture, roughness and infill do however significantly
influence the validity of the cubic law with even its application to smooth parallel
systems being contestable. Rock mechanical discontinuity surveys provide valuable
information regarding the discontinuity geometry that can likely contribute to the
evaluation of flow through individual fractures with variable properties. The hydraulic
aperture is available for the transmission of flow, while normal and shear stresses alter
discontinuity properties over time. In this, numerous advances have been made to
better accommodate deviations of natural discontinuity geometry to that of smooth
parallel plates and at partial saturation. The paper addresses these advances and details
conditions under which the cubic law, even in local form, fails to adequately estimate the
hydraulic properties. The role of roughness in open discontinuities is addressed in
particular, as contact areas and high amplitude roughness cause most extensive
deviation from the cubic law. Aperture of open fractures still governs hydraulic
properties, but inertial forces control flow in very rough fractures, in which instances
the applicability of the cubic law should be revisited. Open questions are finally posed,assessment of which will contribute significantly to the understanding of flow through
individual discontinuities as well as fracture networks.
