Strike–Slip Fault Reactivation Triggered by Hydraulic-Natural Fracture Propagation during Fracturing Stimulations near Clark Lake, Alberta

The fluid diffusion pathways through intricate hydraulic–natural fracture networks may lead to fault reactivations. However, the underlying mechanisms are still not well understood. In this article, we present case studies to investigate the strike–slip fault reactivation triggered by hydraulic–natural fracture propagation during fracturing stimulations. The unconventional fracture model (UFM) is built to simulate the real-time propagation of hydraulic fractures and the interaction between hydraulic and natural fractures. The Mohr–Columb failure criteria are employed to determine the fault reactivation under the UFM during or after fracturing stimulations. The following are found: (1) The results of triaxial stress experiments of 27 core samples for the key well determine the static Poisson’s ratio and Young’s modulus of 0.258 and 48.7 GPa, respectively. (2) The average strike azimuths of associated natural fractures are NE 55° and SW 260°. The fault is recognized with the strike azimuth of NW 15° and fault length of 1510 m. (3) The unconventional fracture model takes into account hydraulic fracture initiation, hydraulic–natural fracture interactions, and stress shadow effects. (4) The occurrence of M3.9 was due to fluid injection during the eight stage completions of H4. The actual increase in pore pressure and Coulomb failure stress reached 3.21 and 1.93 MPa, exceeding the threshold value of Fault 1 and triggering the M3.9-induced earthquake. The insights on triggering mechanisms will guide seismicity-free fracturing stimulations in future shale development.