Investigation on Two M<sub>w</sub> 3.6 and M<sub>w</sub> 4.1 Earthquakes Triggered by Poroelastic Effects of Hydraulic Fracturing Operations Near Crooked Lake, Alberta
Gang Hui, Shengnan Chen, Zhangxin Chen, Yongming He, Shuhua Wang, Fei Gu
Abstract
Abstract A coupled approach of fluid flow and geomechanics is proposed in this study to quantitatively understand the hydraulic fracturing‐induced poroelastic effects that activate pre‐existing faults and trigger earthquake swarms near Crooked Lake, Alberta. The 3D poroelastic simulation of the seismogenic fault zone is then conducted to characterize the pressure diffusion and stress perturbation that led to fault activation. Results show that the poroelastic effects on the high‐permeable damage zones of a conductive‐barrier fault triggered the sequential activation of the seismogenic fault in the basement and Winterburn Formation. In addition, the high‐permeable damage zones act as conduits for pore pressure diffusion along the fault, whereas the fault core functions as a barrier to prevent crossing flow. The poroelastic effects in terms of pressure diffusion and stress perturbation in response to fluid injection facilitated the fault slip and hence triggered the M w 3.6 earthquake in the basement formation 40 days after the fracturing operations. Moreover, the mainshock created negative Coulomb failure stress changes, inhibiting further fault slip in the basement formation. Subsequently, the stimulation of another well facilitated poroelastic effects on the fault damage zone in top Winterburn Formation, reactivating the same fault with an M w 4.1 earthquake 8 days after the initiation of treatments. It is essential to optimize the injection site selection near the existing faults to reduce risks of the induced earthquakes near Crooked Lake.