Topology and distribution of deformation bands in normal fault damage zones, Utah
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Deformation bands are common strain localization features in porous rocks and sediments that occur as millimeter to centimeter wide tabular zones. They may occur as single bands, network of bands or in clusters and are precursors to faulting in the extensional regime. The geometry and distribution of deformation bands in and fault damage zones have been the subject of several studies and is well documented in the literature. However, the network properties and how deformation bands relate to each other are less established, prompting this study. In this thesis, an extensive topological analysis of deformation band networks within the damage zones of the extensional Big Hole Fault and the Delicate Arch Ramp in eastern Utah is presented. The studied section of the Big Hole Fault is a wall damage zone where the deformation bands are cropping out in the Navajo Sandstone. The Delicate Arch Ramp is bounded by two soft-linked normal faults and is classified as a relay damage zone. The deformation bands in the relay damage zone are cropping out in the Slick Rock Member of the Entrada Sandstone. The deformation band networks are assessed in terms of their geometry, distribution and topology. Topological analysis show that the studied deformation band networks are Y-node and C-C branch dominated resulting in very high average connectivity. These characteristics are very similar in the two damage zones despite the distribution and geometry of bands being different. The Big Hole Fault damage zone is relatively narrow, has high deformation band intensity and bands that are predominantly subparallel to the fault. The Delicate Arch Ramp has a wider damage zone where deformation is more distributed throughout the ramp area. Analysis using density grids reveal that there are significant changes in the connecting node frequency and deformation band intensity along strike in the Big Hole Fault area. High deformation band intensity occurs in areas where deformation band segments link up, bifurcate or intersect. These areas are associated with densely spaced bands with more variable orientations, resulting in compartmentalization of the host rock. Because the high intensity areas contain more bands, it would be more difficult for fluid to move through these regions. However, the areas with lower deformation band intensities could act as leakage points in a production scenario or lead to increased tortuosity for fluid flow.
PublisherThe University of Bergen
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