Investigating the role of elastostatic stress transfer during hydraulic fracturing-induced fault activation

Tom Kettlety, James P. Verdon, Maximilian J. Werner, Michael Kendall, & Jessica Budge

Under Review November 28, 2018, SCEC Contribution #8961

We investigate the physical processes that generate injection-induced seismicity, speci fically during hydraulic fracturing-induced fault activation. Fluid processes (increases in pore pressure and poroelastic stress) are often considered to be the primary drivers. However, some recent studies have suggested that elastic stress interactions may signifi cantly contribute to further seismicity. In this work we use a microseismic dataset acquired during hydraulic fracturing to calculate elastic stress transfer during a period of fault activation and induced seismicity. We find that elastic stress
changes may have weakly promoted initial failure, but at later times stress changes generally acted to inhibit further slip. Uncertainties in source mechanism and model parameters are then considered, resulting in the positive signal being further weakened. Sources from within tight clusters are found to be the most signifi cant contributor to the cumulative elastic stress changes. Given the estimated in situ stress eld, relatively large increases in pore pressure are required to reach the failure envelope for these faults -- on the order of 10 MPa. This threshold is far greater than the cumulative elastic stress changes found in this study, with the vast majority of events receiving no more than 0.1 MPa. This large magnitude di fference further indicates that elastic stress changes were not a signifi cant driver, and that interaction with the pressurised fluid was required to initiate failure. Thus, small-scale stress transfer from events near the well did does not appear to play a signifi cant role in the reactivation of nearby non-critically stressed faults.

Key Words
induced seismicity, Coulomb stress, earthquake interaction and triggering

Kettlety, T., Verdon, J. P., Werner, M. J., Kendall, M., & Budge, J. (2018). Investigating the role of elastostatic stress transfer during hydraulic fracturing-induced fault activation. Geophysical Journal International, (under review).

Related Projects & Working Groups
Collaboratory for the Study of Earthquake Predictability, Earthquake Forecasting and Predictability