  A multi-scale scheme for the invasion percolation of rock fracture networks
with heterogeneous fracture aperture fields is proposed. Inside fractures,
fluid transport is calculated on the finest scale and found to be localized in
channels as a consequence of the aperture field. The channel network is
characterized and reduced to a vectorized artificial channel network (ACN).
Different realizations of ACNs are used to systematically calculate efficient
apertures for fluid transport inside differently sized fractures as well as
fracture intersection and entry properties. Typical situations in fracture
networks are parameterized by fracture inclination, flow path length along the
fracture and intersection lengths in the entrance and outlet zones of
fractures. Using these scaling relations obtained from the finer scales, we
simulate the invasion process of immiscible fluids into saturated discrete
fracture networks, which were studied in previous works.
