N.E. Odling, S.D. Harris, E. McAllister and R.J. Knipe
RDR, School of Earth Sciences, University of Leeds, Leeds
LS2 9JT, UK
Natural fault damage zones are composed of clusters of sub-seismic scale faults surrounding larger faults that together form a complex deformation volume or damage zone. The case of the zone as a barrier to flow is considered. We use a statistical model of a fault damage zone that includes fault clustering and power law size distribution of faults. Slices through this model are used as input to a 2D discrete fracture flow model to investigate the scaling properties of bulk rock permeability for sample areas in the range 5 to 50m, size distribution exponents of 1.8 and 2.2, and clustered and random spatial distributions. The degree of ‘efficiency’ of the fractured regions (50 by 50 m) is characterized by comparing bulk permeability of the model to that of the same region with a single fault perpendicular to flow, containing the same proportion of fault rock. Regions 50 by 50 m are found to be around 50% efficient perpendicular to the fault and between 1% and 10% efficient parallel to the fault. The model results perpendicular to the fault for (1/K-1) show a power law scaling effect with an exponent (slope of the graph) of around 1.2. This indicates that as the proportion of fault rock increases, the efficiency of the network decreases in a power law fashion.