Microseismic monitoring has become a tool of choice for the development and optimization of oil and gas production from unconventional reservoirs. The primary objective of (micro) seismic monitoring includes localization of (micro) seismic events and characterization of their source mechanisms. Most seismic events are of a nonexplosive nature, and thus, there are waveform (polarity) differences among receivers. Specifically, double-couple sources represented a challenge for migration-based localization techniques. We developed and applied a new migration-type location technique combined with source mechanism inversion that allowed for constructive interference of signal in seismic waveforms. The procedure included constructing image functions by stacking the amplitudes with compensated polarity changes. The compensation weights were calculated by using moment tensor inversion. This method did not require any picking of arrivals at individual receivers, but it required receivers to be distributed in multiple azimuths and offsets. This made the technique suitable for surface or near-surface monitoring, in which a low signal-tonoise ratio (S/N) can be overcome by stacking. Furthermore, the advantage of this technique was that in addition to the position in time and space, we also determined the source mechanism. We determined with numerical tests that the proposed technique can be used for detection and location of events with S/Ns as low as 0.05 at individual (prestacked) receivers. Furthermore, we found that other source mechanism parameters such as magnitude, volumetric, or shear components of the source mechanism were not suitable for the location. Finally, we applied the proposed technique to a microseismic event of moment magnitude −0.3 induced during the hydraulic fracturing treatment of a gas shale reservoir in North America.

Microseismic monitoring is an important tool for development and optimization of oil and gas production from unconventional reservoirs, which includes localization of microseismic events and characterization of their source mechanisms. We propose a new migration-type technique combined with the source mechanism inversion for simultaneous microseismic events and source mechanism determination. The advantage of this method is that it does not require any picking of arrivals at individual receivers. Numerical tests show technique robustness to noise, even weak events in data sets with signal-to-noise ratio of 0.05 can be localized. Finally, we demonstrate a successful field data application for a microseismic event occurred during the hydraulic fracturing of a gas shale reservoir in North America.

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