Overview The goal of this document is to highlight the current state of knowledge governing different aspects of the hydraulic fracture propagation process characteristic of many stimulation operations. Specific emphasis is placed on how observations of seismic sources can be used to infer the production behavior of the reservoir. Failure of Rock and Rock Interfaces For the case of a propagating fracture due to hydraulic fracture stimulation, micro--seismic data collected from a number of

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... ts indicate bulk fracture propagation of O(10 1 ) m/s << O(10 3 ) m/s for the sound speed in intact rock. This is counter--intuitive when considering fracture mechanics, where fractures in tension (Mode I) generally propagate near the Rayleigh wave speed. If we resort to theoretical consideration of fluid--driven fractures in an elastic medium, the anecdotally observed propagation velocity noted above is recovered [1] = 4 !" ! !! ,