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States of in-situ stress in the Duvernay East Shale Basin and Willesden Green of Alberta, Canada: variable in-situ stress states effect fault stability
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  • Luyi W Shen,
  • Douglas Ray Schmitt,
  • Ruijia Wang,
  • Tyler E. Hauck
Luyi W Shen
Department of Physics, University of Alberta, Department of Physics, University of Alberta

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Douglas Ray Schmitt
Purdue University, Purdue University
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Ruijia Wang
University of New Mexico, University of New Mexico
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Tyler E. Hauck
Alberta Geological Survey, Alberta Geological Survey
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Fault slip is controlled by the normal and shear tractions on a fault plane. A full understanding of the factors influencing induced seismicity requires quantitative knowledge of the in-situ stress tensor and fluid pressure. We analyze these variables for a 200 km × 200 km region with active hydraulic fracturing near the city of Red Deer, Canada. The levels of induced seismicity in the area were generally low before Mar 04, 2019, MW 3.8/ML 4.2 event that local residents felt. We use geophysical logs and pressure tests within the targeted Duvernay Formation to construct maps of ambient pore pressure, vertical and minimum horizontal stresses. Maximum horizontal stress is constrained from the focal mechanism inversion and borehole-based estimation method. We find a broad range of orientations are susceptible to slip and small perturbations of fluid pressure would promote displacement. This suggests that the differential variations in pore fluid pressure in the target formation may provide a metric of slip susceptibility; a map for the study area is developed. Areas of high susceptibility correlate with those experiencing higher levels of induced seismicity except for the Willesden Green oil field that has similarly elevated susceptibility and active hydraulic fracturing operations. The methods and results demonstrate how more quantitively constrained in-situ stresses developed from an ensemble of real field measurements can assist in assessing fault stability and in developing metrics for slip susceptibility.
Jun 2021Published in Journal of Geophysical Research: Solid Earth volume 126 issue 6. 10.1029/2020JB021221