Abstract: Microstructural and Diagenetic Evolution of North Sea Fault Zones

Susan J. Haggerty

The deformation mechanisms and diagenetic events that determine the evolution of the fluid-flow properties of North Sea faults have been established by characterization of faults in core and thin section. The results of this study have implications for predicting fault seal and fault-migration potential.

Independent particulate flow allowed ductile smearing of sand and shale units in North Viking Grahen fault zones via grain disaggregation and rotation. Cataclasis produced fine-grained fault gouge in sand-rich lithologies in southern North Sea fields. The cataclasis has resulted in fault cross-seal even where sand/sand juxtaposition occurs.

Capillary pressure measurements of the deformed samples indicate that both independent particulate flow and cataclastic deformation mechanisms result in relatively low-permeability fault zones. Preliminary calculations using the capillary pressure results suggest, however, that faults with good sealing potential can allow hydrocarbon migration over geologic time scales.

Cements are commonly observed within the North Sea fault zones; these cements also contribute to the observed permeability reduction. Current research will establish the relative and absolute timing of faulting and cementation to determine whether the cement precipitates as a result of focused fluid flow during fault activity, or after fault movement.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994