Fluid injection is well known to in certain conditions trigger fault slip and associated seismicity. Concerns around injection induced seismicity has grown over the past few years as suspected cases of induced seismicity have been raised, specifically resulting from salt-water disposal and hydraulic fracturing. Of the many reservoirs in the WCSB undergoing hydraulic fracture stimulation, three particular reservoirs have experienced felt seismicity: Horn River Basin, Montney and Duvernay. Similar to other instances of injection induced seismicity, the mechanism is considered to be elevated pore pressure reducing the effective clamping stress and facilitating slip of stored tectonic stress. Typically seismic monitoring is used to create a ‘traffic light system’ where operations are slowed and ultimately stopped if the strength of recorded seismicity exceeds preset limits. 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 microseismic geomechanics, the seismic activity can be predicted and used to calibrate to the actual seismicity monitored during the fracture treatment. In this study, the impact of the hydraulic fracturing on a pre-exisiting 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 corresponding with fracturing into the discrete fracture network and a pre-existing fault. 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.
AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016