Abstract Damage zones of different fault types are investigated in siliciclastics (Utah, USA), carbonates (Majella Mountain, Italy) and metamorphic rocks (western Norway). The study was conducted taking measurements of deformation features such as fractures and deformation bands on multiple 1D scanlines along fault walls. The resulting datasets are used to plot the frequency distribution of deformation features and to constrain the geometrical width of the damage zone for the studied faults. The damage-zone width of a single fault is constrained by identifying the changes in the slope of cumulative plots made on the frequency data. The cumulative plot further shows high deformation frequency by a steep slope (inner damage zone) and less deformation as a gentle slope (outer damage zone). Statistical distributions of displacement and damage-zone width and their relationship are improved, and show two-slope power-law distributions with a break point at c. 100 m displacement. Bleached sandstones in the studied siliciclastic rocks of Utah are associated with a higher frequency of deformation bands and a wider damage zone compared to the unbleached zone of similar lithology. Fault damage zones in the carbonate rocks of Majella are often host to open fractures (karst), demonstrating that they can also be conductive to fluid flow.

Abstract: The boundaries between pairs of adjacent fault segments within normal fault arrays define a spectrum of structures, from relay ramps where the length of overlap between the fault segments is much larger than the separation, through low aspect ratio (overlap/separation) relay ramps and ultimately to underlapping fault segments. Where fault segments underlap, transfer of displacement between them is accommodated by a connecting monocline. When displacement increases and a through-going fault forms, relay ramps are preserved as fault-bounded zones of elevated bed dip and monoclines are preserved as areas of normal drag. Therefore, the orientation and magnitude of bed dips within and adjacent to a fault zone, and the numbers of segments seen on a cross-section through it, depend largely on the aspect ratios of relay ramps in the initial fault array. The aspect ratio of relay ramps varies between different fault systems. An analysis of the geometry of 512 relay ramps from 13 different fault systems suggests that the main controls on aspect ratio are the strength of the sequence at the time of faulting and the underlying structure.

Abstract Interpretation of faulted reservoirs is hindered by an industry-wide lack of structural specialists, which in turn hinders the development of structurally proficient interpreters. This can have expensive consequences, including poor models of dynamic flow in reservoirs, erroneous calculations of reserves, and difficulties during well drilling. Focused training using paper maps, outcrop visits, and digital models of the same structures helps to introduce and reinforce concepts. The first component of the training is to provide participants with a set of two-dimensional seismic lines created from a geological model of a faulted reservoir. Participants must create a structure contour map containing faults that honor simple rules such as conservation of throw at fault intersections, identification of fault tips, consistent sense of offset and vergence along strike, and identification of fault relays. The second component is a visit to the outcrop from which the paper map was derived, providing the opportunity to discuss differences between faults in outcrop and faults as visible on seismic data. The final component provides participants with a digital model of the outcrop, giving them the opportunity to create a geologically valid interpretation that can be used for fault property prediction or reservoir model creation. This three-pronged training provides grounding in structural geology and lets interpreters know the rules that their fault framework models should obey. Applying these techniques during interpretation saves time by ensuring that “busts” are caught and fixed before they become institutionalized, and also closes the gap between the geophysicist/seismic interpreter and the geologist/static modeler.