Geomechanical modeling of induced seismicity resulting from hydraulic fracturing

Abstract

The number of instances of induced seismicity associated with hydraulic fracturing has increased over the last few years, resulting in the development of industry protocols to mitigate seismic hazard. The main focus of these protocols is “traffic-light” systems based on seismic monitoring, in which operations are modified if a specified “yellow-light” magnitude level is reached or ultimately are stopped at a “red-light” magnitude. A variety of operational changes is possible to mitigate the seismic hazard at the different traffic-light levels, including slowing injection rate or volume, skipping stages, or ultimately stopping or flowing back the well. Empirical evidence of induced-seismicity magnitudes, including microseismic-imaging projects in which no induced seismicity occurred, are inconclusive about the impact of changing volume or rate. Although the largest observed magnitudes occur at large injection volumes, significant variability in magnitudes is found for both injection rate and volume. Alternatively, a geomechanical simulation can examine pore-pressure diffusion and mechanical stresses and strains associated with hydraulic-fracture treatments and can be used to model fault activation and corresponding estimates of seismic magnitudes. These geomechanical models complement monitoring-based traffic-light systems and can be used to test various operational changes to identify a scenario that reduces seismic hazard.