Comparison of migration-based location and detection methods for microseismic events

Microseismic monitoring in the oil and gas industry commonly uses migration-based methods to locate very weak microseismic events. The objective of this study is to compare the most popular migration-based methods on a synthetic dataset that simulates a strike-slip source mechanism event with a low signal-to-noise ratio recorded by surface receivers (vertical components). The results show the significance of accounting for the known source mechanism in the event detection and location procedures. For detection and location without such a correction, the ability to detect weak events is reduced. We show both numerically and theoretically that neglecting the source mechanism by using only absolute values of the amplitudes reduces noise suppression during stacking and, consequently, limits the possibility to retrieve weak microseismic events. On the other hand, even a simple correction to the data polarization used with otherwise ineffective methods can significantly improve detections and locations. A simple stacking of the data with a polarization correction provided clear event detection and location, but even better results were obtained for those data combined with methods that are based on semblance and cross-correlation.