A coupled hydro-mechanical model is used to evaluate fault activation associated with hydraulic fracturing in the Horn River Basin. The model is used to simulate hydraulic fracture growth through a discrete fracture network, examining the pore pressure diffusion and associated fracture dilation and shearing. Based on the geomechanics, the seismic activity can be predicted and used to compare with the actual seismicity monitored during the fracture treatment. The synthetic microseismic prediction includes location, timing and magnitude of the activity and can be used to validate the geomechanical attributes and calibrate the model to match the field data. Applying such a microseismic geomechanics approach not only improves the interpretation of the microseismic image but also improves the understanding of the geomechanical response of the reservoir.
In this study, the impact of the hydraulic fracturing on a preexisiting fault was examined to quantify seismic hazard. A geomechancial model was created to investigate a Horn River Basin hydraulic fracture and the associated seismic magnitudes. The model was designed to investigate the mechanism of fault activation and the impact of fracturing at different locations around the fault. The study indicated that the stimulated fracture network had to grow directly into the fault in order for the injection pressure front to trigger fault slip. Geomechanical assessment of absolute seismic hazard can be used to modify the engineering design prior to operations to minimize the seismic hazard including the placement of the well, and modifiy staging along the well to avoid fracturing in the regions likely to lead to fault activation. In scenarios where induced seismicity occurs during the treatment, the method can also be used to examine operational changes to lessen the relative seismic hazard.
With hightened public concerns of environmental issues with hydraulic fracturing, attention is raising around the few isolated cases of injection-induced seismicity. An increasing number of reports have recently been made of felt seismicity associated directly with hydraulic fracture treatments or disposal of waste water from extraction of unconventional resources. In order to safely and efficiently develop unconventional reservoirs in areas of concern, industry protocols have been developed to deal with induced seismicity issues. Typically these protocols rely on local seismic monitoring to define traffic light systems, where operations are modified depending on the seismicity levels. As part of these protocols, methodologies are required to assess the seismic hazard both prior to the initiation of operations in addition to modifications to planned operations when required by traffic light levels.