Maps of the in situ stress directions and magnitudes at the depth of the Duvernay Formation within the Alberta Energy Regulator's Kaybob assessment area centered at the town of Fox Creek, Alberta were constructed from multiple sets of oriented borehole images, density logs, and static and dynamic wellbore pressure tests collected from nearby boreholes that targeted the Duvernay Formation. Interpreted azimuths of borehole breakouts and drilling-induced tensile fractures through borehole image logs reveal that the orientation of maximum horizontal compressive stress (SH) in the Kaybob assessment area is dominantly northeast-southwest, mainly in agreement with the typical stress directions throughout much of the Alberta Basin. Vertical-stress magnitudes (SV) come from estimates of the overburden pressures obtained by integration of more than 1000 smoothed density logs (more than 600 of which fall within the Kaybob assessment area), indicating stress to depth ratios of between 24 and 26 kPa/m for the Duvernay Formation at depths ranging between 2800 and 4000 m in the area near Fox Creek.

Dynamic borehole-pressurization tests, variously referred to as minifrac, microfrac, and diagnostic fluid-injection tests (DFITs), were reanalyzed using a consistent procedure to find the fracture-closure pressure (PFC), which is here taken to be equal to the minimum horizontal compression (Sh). The closure pressure was measured as ~60 MPa at 2800 m depth, increasing to ~85 MPa at 3800 m. Minimum stress to depth ratio is constrained to between ~17 and ~22 kPa/m for the study area. Pore pressures (PP) were also estimated from the pressurization tests. The computed average pore pressure for the Duvernay Formation near Fox Creek is estimated at ~55 MPa (2800 m) to ~80 MPa (3800 m). The pore pressure to depth ratio ranges from ~10 to ~21 kPa/m and demonstrates considerable overpressure.

NTS Keywords

Shen, L., Schmitt, D.R., and Haug, K. (2018): Measurements of the states of in situ stress for the Duvernay Formation near Fox Creek, west-central Alberta; Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Report 97, 29 p.