Quantitative states of the in-situ stress of the Canadian Duvernay Formation and deterministic analysis on the regional fault stability

• Author / Creator

  Shen, Luyi

• Maps of the in-situ stress directions and magnitudes at the depth of the Duvernay Formation within the Alberta Energy Regulator’s (AER) Kaybob assessment area (centered on the town of Fox Creek), East Shale basin (centered on the city of Red Deer) and Willesden Green oil field are 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.
  Azimuths of borehole breakouts and drilling-induced tensile fractures interpreted from borehole image logs reveal that the orientation of maximum horizontal compressive stress (SH) in the studied 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 integrating more than 1000 smoothed density logs. Dynamic borehole-pressurization tests variously referred to as minifrac, microfrac, and diagnostic fracture injection test (DFIT), were reanalyzed. A consistent procedure is adapted to find the fracture-closure pressure (PFC), which is here taken to be equal to the minimum horizontal compression (Sh). Pore pressures (PP) were also estimated from the pressurization tests. Stress inversion of the focal mechanism solutions for the earthquakes nearby validated the assumed Andersonian stress regime and provided the shape-ratio of the stress. Combined with borehole breakout observations, we constrained the magnitudes of SH that completes the Andersonian stress tensor.
  It is shown that the ambient pore pressures of the nearby Duvernay unconventional reservoirs can provide enough Pf triggering fault movement. The local fluid pressures acting on the fault can be readily increased above the critical value if a hydraulic connection exists between the fault and a propagating hydraulic fracture within which pressures in excess of the minimum compression exist. The critical pressure necessary to induce slip is estimated using a probabilistic model that incorporates uncertainties of stress and fault’s mechanical properties. These critical pressures are greater than expected hydrostatic pressure but less than the nearby unconventional reservoirs' pore pressures.
  
  We further build another 3D stress model for the areas of Red Deer, which had also been historically seismic quiescent but experienced recent high profile induced earthquakes. A susceptibility map, built on the basis of faulting planes’ slip tendency, shows that the HF-induced clusters geographically overlap with the zones of higher susceptibility. High ambient pore pressure does not correlate with high susceptibility, and large deviatoric stress is needed to cause HF-induced earthquakes.

• Subjects / Keywords

  • geomechanics
  • stress
  • geophysics

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-smxg-7r58

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.