Predicting fracture localization in folded strata from mechanical stratigraphy and fold shape: Case study of east Kaibab Monocline, Utah

Abstract

Joints within folds are often localized within zones. These joint clusters may influence the flow of fluids in the subsurface but are often undetectable on conventional seismic lines. Joints develop in folded strata in response to fold shape and mechanical stratigraphy. Mechanical stratigraphy describes the distribution of layers (layer thicknesses) and the nature of the layer contacts. Within folded strata, joints may localize at regions of high curvature within the outer arc of the fold or at regions of interlayer slip along fold limbs. This study compares the observed fracture pattern within the Navajo Formation at East Kaibab Monocline, Utah with those predicted by numerical models in order to validate the modeling technique. The Boundary Element Method model simulates folding of the Navajo Formation; fold shape and mechanical stratigraphy are estimated from field observations. The numerical model matches the observed fracture pattern while the details of fracture localization will be controlled by heterogeneous interlayer material. The technique presented in this study may be used to predict the location and extent of subsurface joint clusters if fold shape can be resolved from seismic lines and mechanical stratigraphy (layer thickness and contact friction) determined from borehole data.