Outcrop Analogues of Fault Systems Showing Variations in Linkage, Segmentation and Compartmentalisation with Increasing Deformation
The progressive development of a fault zone, in response to ongoing deformation, can give rise to major changes in the potential of the fault to impede or enhance hydrocarbon flow. We show a number of detailed 3D outcrop models of extensional fault systems (captured using terrestrial Lidar) that illustrate typical effects of increasing deformation on fault linkage, segmentation and reservoir compartmentalisation. Examples of low-strain extensional fault systems are often characterised by sparsely distributed, isolated faults and low levels of fault linkage. There is little compartmentalisation, and the likely effects on fluid flow are minor. As deformation accumulates, ongoing fault growth causes increased fault interaction and linkage; i.e. there is a tendency for strain to localise onto a fewer number of larger structures. Mature fault zones that have accommodated large extension are often highly linked. We show an example of a large regional-scale active fault zone, and present evidence to suggest that the host volume is compartmentalised on at least three scales of observation (~10km, ~100m, ~10m). This appears to occur by progressive linkage of fault panels of different orientations (giving rise to curved composite fault surfaces), and by bifurcation of fault panels (so that different parts of a single panel are linked with other panels of different orientations). These processes give rise to complex patterns of 3D fault linkage, and can generate a large amount of low permeability cataclastic fault product that will significantly impede hydrocarbon flow.