N. E. Odling, S. D. Harris, E. McAllister, and R. J. Knipe

RDR, School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK

ABSTRACT: Geometrical and Permeability Properties of Fault Damage Zones

Natural fault damage zones are composed of clusters of sub-seismic scale faults surrounding larger faults which together form a complex deformation volume or damage zone. The connectivity of sub-seismic faults dictates the effectiveness of the zone to act as a barrier or conduit to fluid flow. Here we use a statistical model of a fault damage zone geometry based on observations from natural faults (Harris et al 1999) to provide input to a discrete fracture flow model which is then used to investigate the scaling properties of bulk rock permeability.

The statistical model of fault damage zone geometry assumes that fault sizes follow a power law distribution and that small faults are clustered around large faults. Important variables in this model are the size distribution power law exponent, fault length to width ratio and the fault orientation distribution. The spatial distribution of smaller faults is controlled by the size of the larger faults and thus the major (longest) fault has the greatest proportion of minor faults clustered around it. Models with up to 12 million faults have been generated.  presents a 3D fault damage zone simulation and the geometry of fault traces in 2D cuts through the model, which clearly show the clustered nature of the spatial distribution and the formation of clustered networks.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado