State of In Situ Stress and Implications for Fault Slip Potential in the Montney Play, Western Canada

• Published in: Journal of geophysical research. Solid earth Vol. 130; no. 8
• Main Authors: Han, Hongxue, Baan, Mirko
• Format: Journal Article
• Language: English
• Published: 01.08.2025
• Subjects: fault slip potential; in situ stress; seismicity
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2024JB030976

We investigate slip potentials of major faults in the North Montney Trend (NMT) and the Kiskatinaw Seismic Monitoring and Mitigation Area (KSMMA) in the Western Canada Sedimentary Basin. The KSMMA and NMT are seismic monitoring areas implemented by the British Columbia Energy Regulator (BCER) in 2018 following concerns about the increasing number of felt seismic events during hydraulic fracture treatments within the Montney Play, including the largest recorded (MW=4.6 ${M}_{W}=4.6$) event in the NMT, and another three events (ML=3.6∼4.5 ${M}_{L}=3.6\sim 4.5$) in the KSMMA. Our objective is to explain the observed seismicity from a geomechanics point of view. We first estimate full in situ stresses for the Montney Formation. Magnitude estimation of the maximum horizontal stress is subject to a large uncertainty. We therefore estimate a range of probable values based on the poroelastic stress model, combined with strain corrections inversely proportional to the distance from the Rocky Mountain Fold and Thrust Belt, as well as commonly used constraints from the borehole measurements and the possibility of a critical stress state. Finally, we estimate the likelihood of slip given known fault orientations in the area. We find that a reverse faulting to transpressional stress state exists within the NMT, transitioning to a transtensional to normal faulting regime in the east of KSMMA. The recorded seismicity mainly occurred at transitional in situ stress regime locations, as in these cases fault reactivation can occur on multiple planes. The amount of overpressure has a significantly smaller influence. Our findings help explain observed source mechanisms of moderate‐sized induced earthquakes. Plain Language Summary Hydraulic fracturing of the Montney Formation, a low‐permeability unconventional reservoir in Western Canada, caused multiple moderate earthquakes including an event of MW=4.6 ${M}_{W}=4.6$ that occurred on 17 August 2015, in the North Montney Trend, and another three events (ML=3.6∼4.5 ${M}_{L}=3.6\sim 4.5$) happening on 30 November 2018, near Fort St. John. As a result, the British Columbia Energy Regulator implemented two seismic monitoring areas. We estimate the horizontal and vertical stresses in this Formation as well as its pore pressure distribution in order to explain the locations of the largest concentrations in human‐induced seismicity. We find that seismicity does not necessarily occur in areas with the highest pore pressures. Most recorded seismicity occurred where two principal stresses have similar magnitudes because here fault reactivation can occur on multiple planes. Our findings have implications for managing and mitigating of human‐induced seismicity. Key Points Stresses in the Montney transition from reverse to strike‐slip in the North and strike‐slip to transtensional/normal faulting in the East Induced seismicity concentrates in transitional stress areas where two instead of one fault orientations can be reactivated Overpressure gradients correlate to hydrocarbon maturity but not the largest earthquake concentrations