Outcrop Analogs
of Multi-Layer Fracture Zones
Gross, Michael R.1 (1)
The ability of a fracture network to
transmit fluids in large part depends upon the connectivity, spacings, lengths
and apertures of the fractures. The overwhelming majority of subsurface flow is
accommodated by the largest fractures. Though fewer in number, these
multi-layer fracture zones have the highest transmissivities and are often in
direct hydrologic contact with the more numerous smaller fractures. In order to
assess the contribution of multi-layer fractures to reservoir flow, one must
evaluate their morphological character (e.g., width, planarity, aperture
distribution, roughness, number of segments and how they are linked), the kinematics
of their formation (sense of motion and relation to strain), and their position
within a multi-scale mechanical stratigraphy. To this end, multi-layer
fractures were analyzed for a variety of lithologies and tectonic settings.
Results suggest a common process for the formation of multi-layer fractures in
layered rocks, namely the coalescence and linkage of pre-existing, bed-confined
fractures. Further, geometries of multi-layer fractures change systematically
in response to increasing strain. This allows for the mapping of strain based
on the geometry and frequency of multi-layer fractures, or conversely, the
prediction of fracture intensity based on the spatial distribution of strain.
An understanding of the geometries, origin and hydrologic properties of
multi-layer fractures will contribute to the characterization of fractured
reservoirs and models that more accurately reflect the architecture of natural
fracture networks.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California