Abstract - In their simplest form, brittle faults consist of a single zone of intense deformation which macroscopically is seen as a slip surface and/or a zone of fault rock (e.g. breccia, gouge, shale smear). More generally, fault zones have complex geometries with multiple slip surfaces and/or deformation zones. The most common pattern in complex fault zones observed at outcrop is a fault zone bounded by a pair of sub-parallel slip surfaces. In three dimensions, fault zones bounded by paired slip surfaces alternate both laterally and up/down dip with areas of only one slip surface. Within this overall framework, a range of fault rocks is irregularly distributed as spatially impersistent sheets and lenses.
Due to seismically irresolvable complexities of fault zone structure, across-fault juxtapositions predicted from seismic data will in most cases be different from those actually present. The importance of such differences to the prediction of across-fault connectivity, of both hydraulically passive and active fault zones, is strongly dependent on the reservoir sequence. Connectivities are calculated for faults offsetting an Upper Brent Reservoir sequence for different SGR cut-off values. Shaley fault rocks within brittle fault zones often represent a spatially persistent, though variable thickness, component of the zones and provide a basis for the application of empirical methods of fault seal prediction to brittle faults.
The distribution of fault rocks cannot be characterised from well
data, raising the question of whether purely deterministic methods for
fault seal prediction can ever be successful. The way forward is by refinement
of current empirical methods by achieving more detailed characterisation
of sub-surface faults allowing more quantitative comparison between target
faults and those of known sealing behaviour.
In: Hydrocarbon seals - Importance for exploration and production.
(Eds. Møller-Pedersen, P. & Koestler, A. G.), Norwegian Petroleum
Society (NPF), Special Publication 7, 61-72, 1997.