Characterization of faults and fractures in basement rocks, implications for fault initiation and growth

Abstract

Faults represent high-strain zones in which the fault core accommodates most of the intense deformation. The surrounding damage zone is linked to slip accumulation, and its architecture has important implications for the fault growth and its evolution. Fracture networks are particularly difficult to predict and describe in the subsurface since they are generally below the resolution of seismic surveys. The presence of fracture networks could play a key role in subsurface operations, where they may locally breach reservoir cap rock, act as conduits for fluid flow, and lower rock bulk strength. Studies have shown a scaling relationship between fault and fracture properties; hence knowledge of fault properties in seismic sections could allow for prediction of the surrounding fracture network. This thesis describes and quantifies the changes in fracture attributes, such as frequency, orientation, aperture and length around faults. In addition, the factors driving fault initiation and propagation have been studied. This approach enables estimation of damage zone width and displacement, two crucial parameters in faulting. The results show that the linkage of individual fractures and the presence of conjugate Riedel shear zones has played a key role in early fault initiation and propagation. In addition, we raise the possibility that the Øygarden Complex is affected by more recent, possibly present-day movements. Current data from metamorphic basement rocks is relatively scarce. The results of this study could serve as an analogue for similar conditions in the North Sea and enable better fault prediction models in the subsurface.