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Microseismic monitoring was used to image hydraulic fracturing during a gas well stimulation. Some time after the end of the injection, there was an increase in the seismic deformation rate. Investigation of the frequency-magnitude characteristics during the pumping phase were consistent with other hydraulic fracture results, although the activity recorded after the end of pumping was more consistent with observations of natural seismic deformation along faults. The ratio of p-to s-wave amplitudes also varied for events recorded during the pumping compared to those occurring after the end of pumping, suggesting a different failure mechanism. In this example, it appears that the hydraulic fracture induced movement on a nearby fault. Geomechanical modeling was also performed to examine induced stresses associated with the stimulation, and investigate possible fault deformation.

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Hydraulic-fracture microseismicity is interpreted for cases in which persistent dip-slip or strike-slip mechanisms exhibit shear planes prevalently aligned close to the principal stress direction. Explaining the preferential alignment in terms of stress changes driven by elevated pore pressure on a Mohr diagram is difficult. Instead, it is proposed that the microseismic shearing is driven primarily by the strain of hydraulic-fracture opening. The interpretation is based on the analog of structures and deformation commonly associated with natural joint growth in layered rock. Specifically, by considering the alternate, horizontal nodal plane as the slip plane for the aligned dip-slip events, one can associate the shearing with a vertical hydraulic fracture stepping over or jogging along bedding planes and generating bedding-plane slip. For the aligned strike-slip events, it is proposed that the critical shearing is generated by breakup of the hydraulic fracture into en echelon fringe fractures near bedding surfaces. In both cases, the shearing represents a tearing mode (mode III) in which the microseismicity highlights the deformation at and near bedding boundaries as the hydraulic fracture rips through or along layer interfaces.

A B S T R A C TBorehole seismic addresses the need for high-resolution images and elastic parameters of the subsurface. Full-waveform inversion of vertical seismic profile data is a promising technology with the potential to recover quantitative information about elastic properties of the medium. Full-waveform inversion has the capability to process the entire wavefield and to address the wave propagation effects contained in the borehole data-multi-component measurements; anisotropic effects; compressional and shear waves; and transmitted, converted, and reflected waves and multiples. Full-waveform inversion, therefore, has the potential to provide a more accurate result compared with conventional processing methods.We present a feasibility study with results of the application of high-frequency (up to 60 Hz) anisotropic elastic full-waveform inversion to a walkaway vertical seismic profile data from the Arabian Gulf. Full-waveform inversion has reproduced the majority of the wave events and recovered a geologically plausible layered model with physically meaningful values of the medium.