Constraining in Situ Stresses in Southern Saskatchewan, Canada

The in situ stress regime is one of the most important inputs for any subsurface project in civil, mining and petroleum engineering, and combined with soil and/or rock strength generates a geomechanical model, which can be used to predict the ultimate loading that geological materials can withstand, and the required type of mechanical support needed to ensure the structural integrity of any excavation, such as tunnels, shafts, and boreholes. In this work we describe a comprehensive workflow that was carried out to constrain the in situ stress regime in the southern Saskatchewan region, Western Canada. The in situ stress regime was constrained by a geomechanical modeling approach, using acquired petrophysical wireline logging in boreholes, rock strength properties measured on core samples through triaxial tests, and micro-fracturing tests carried-out at different depths along a borehole. This complete dataset significantly contributed to the reliability of the in situ stress characterization, as the microfrac tests, mainly in shallow horizons, constrained the Minimum Horizontal Stress gradient, whilst borehole imaging showed rock failure patterns at the borehole wall (breakouts and fractures) and provided a way of constraining the Maximum Horizontal Stress by reproducing the rock failure with geomechanical modeling. The constrained stress regime exhibits a transition from shallow to deep horizons, and overall is under a strike slip faulting condition. The results of this study greatly contribute to a better understanding of present day subsurface stresses in the region.