A kinematic trishear model to predict deformation bands in a fault-propagation fold, East Kaibab monocline, Utah

Abstract

Well core with numerous deformation bands in the reservoir interval may or may not be indicative of reduced effective reservoir permeability at the scale of well drainage areas. Many dense concentrations of deformation bands are related to the damage zone of a larger fault. However, some populations are more broadly distributed. We analyze one such population associated with the East Kaibab monocline in southern Utah. A kinematic trishear analysis is compared with field-based strain measurements. We find that the widespread dense deformation-band populations correspond to a broad zone of relatively high strain across the structure. Fault-damage zone models are inadequate to explain these occurrences. Our results show that, where deformation bands are known to occur from core in a folded reservoir, finite strains can be used to estimate their lateral and volumetric extents. However, we also find that the orientations of deformation bands predicted by our modeling are highly sensitive to the strain path. This indicates that path-independent methods for estimating strain such as curvature analysis are not fully appropriate for application to deformation bands. Ultimately, any such method requires information relating rock properties with propensity to form deformation bands to be predictive.