An efficient diffraction stacking interferometric imaging location method for microseismic events

Abstract

Migration-based location methods automatically obtain microseismic event locations without manual picking and often are used in microseismic monitoring during hydraulic fracturing. They use waveform stacking over all receivers to enhance the ability to detect weak events. However, these methods may fail to effectively increase the signal-to-noise ratio (S/N) of the stacked trace and may not obtain an accurate source location if polarity reversals occur in seismic records. To overcome this problem, traditional approaches rely on polarity correction by characteristic function or polarity determination by source moment-tensor inversion and focal mechanism search. To ensure location accuracy and efficiency, we have developed the diffraction stacking interferometric imaging (DSII) method for locating microseismic events. We first obtain the approximately symmetrical pattern responding to the source moment tensor by using diffraction stacking (DS) and then apply interferometric imaging to focus the pattern onto its center and extract the source location. The DSII method overcomes the inaccurate location problem under polarity reversal caused by source mechanisms, and it also benefits from the high efficiency and noise suppression of the DS. Moreover, the symmetrical pattern in the DS source image also can be used as a means of quality control for field data. We use synthetic and field data to demonstrate the location ability of this method. Our results indicate that the DSII can efficiently reduce the effects of strong noise on event detection and location. We can achieve a quasi-symmetrical pattern on the DS image and obtain a focused interferometric image when the velocity has systematic errors. Compared with the DS, the DSII method also has a better performance on sparse-receiver networks. Finally, the DSII method is applied to field data acquired using a surface array during hydraulic fracturing.