Heterogeneity Versus Anisotropy and the State of Stress in Stable Cratons: Observations From a Deep Borehole in Northeastern Alberta, Canada

Geophysical logs collected from a deep borehole drilled into the North American Craton in Northeastern Alberta shed valuable light on state of stress stable cratons. Observed breakout azimuths rotate between three depth intervals, ranging 100° at 1650-2000 m to 173° 2000-2210 m, and finally 145° bottom. No apparent fractures that might have disturbed field were found. Two potential causes these rotating breakouts can be either heterogeneous or elastic strength anisotropy formation. The latter interpretation is favored since observed are strongly controlled by rock metamorphic textures, as validated their close correlations with dip directions foliation planes polarization dipole sonic logs. Monte Carlo realizations further demonstrate anisotropic rocks subjected uniform horizontal direction could result azimuth-rotating breakouts. Stress magnitudes inferred this analysis, which incorporates weak failure planes, suggest normal faulting regime maximum compressive consistent overlying Western Canadian Sedimentary Basin (NE-SW) motion plate. low Mohr-Coulomb analyses formation not near critical condition for slip planes. However, more detailed investigations should conducted calculations indicate widths, particularly when conventional Kirsch-based formula employed, highly nonunique, allowing large variations states.