Edwards, Ewart¹, Ned Porter¹, Tim Needham¹, Rob Knipe¹, Russell Davies¹, Phil Jones¹, Quentin Fisher¹, Anren Li¹, Graham Phillips¹, Mike Kay¹, Diana Condliffe¹
(1) Rock Deformation Research, Leeds, United Kingdom

ABSTRACT: Sub-seismic Fault Zone Architecture Characterisation from Core and Outcrops

Structural analysis of over sixty core and field examples of fault damage zones, primarily with seismic scale throws, provides a basis for detailed characterisation of fault zone architecture. This allows the comparison between analogue faults in outcrop with zones, critical to hydrocarbon sealing, caught in core. The data set provides insights into the fault zone size, minor fault populations and the deformation processes involved in generating faults in sequences with varying net to gross ratios and layered heterolithic sequences. The study also highlights the importance of deformation conditions and reactivation on faulting processes and on sealing capability. Cored damage zone examples presented include faults from the critical plays in the North Sea province, particularly the sand-rich Permian Rotliegendes and the layered sand-shale Jurassic deltaic-shallow marine sequences of North Sea grabens. Data from outcrop concentrate on continental sandstones and paralic sequences from onshore in the UK and Utah, USA. The key factors highlighted include assessment of relationships between; damage zone size, internal geometry, cumulative fault throw, and strain for different net:gross fractions; the localisation of deformation within the principal slip zone or gouge zone of large faults; fluidisation/injection and deformation ‘mixing’ in early-formed over-pressure zones; and the critical re-seal or breach effects seen as cemented faults or open fractures formed in response to local kinematics and regional inversion of pre-existing trap-defining fault zones. The value of structural analyses of core for reservoir characterisation and modelling is emphasised and results from the N Sea are assessed with reference to other hydrocarbon provinces.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.