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Rupture Characteristics and Energy Budget for Activated Fractures During Hydrauliuc Fracture Stimulations


We investigate the failure process of micro-seismic events induced during a hydraulic fracturing shale completion program in NE British Columbia, Canada. The micro-seismic events were well recorded by a hybrid system consisting of multi-well-arrays of high frequency geophones located near the source and arrays of accelerometers and low-frequency geophones deployed near the surface. The hybrid system captures a larger bandwidth than typical recording systems, allowing for the integrated analysis of the source signal and rupture process at various scales. The induced micro-seismic events were located below the treatment area and were large enough (>M1) to be captured by the near-surface arrays. The deeper event locations and larger magnitudes of these events when comparing with the characteristic hydraulic fracture events in this treatment program indicates they are generated by a different mechanism and result from the re-activation of deep pre-existing faults. We calculate source parameters for these events, such as static and dynamic stress drops, apparent stress, source radius, radiated energy, and seismic efficiency using a spectral analysis method. We also estimate the full moment tensor and fracture plane of the events correlating the stress release with the effective normal stress and weakening mechanism by increasing pore pressure. Further, we calculate rupture velocities and analyse the energy budget and rupture complexity as it provides constraints on the initiation and healing of the rupture mechanism, where high frequencies relate to fault edge effects and breaking of asperities and low frequencies with the overall slip on the fault.