Microseismic migration by semblance-weighted stacking and interferometry

摘要

Migration-based methods are attractive for microseismic event location because they can automatically locate the events without manually picking P- and S-wave arrivals. For real-time processing, computational efficiency is important. In this study, we develop an efficient migration-based microseismic location algorithm for 3C data recorded in borehole. We use semblance-weighted stack to detect the moveout curves of P and S waves along the receiver array, then use cross-component cross-correlation on the semblance-weighted stack to create a map of the brightness function with consideration that the polarizations of P and S waves are almost orthogonal. To avoid wrong locations caused by cross-correlation between S wave and its multiples, the brightness function is divided by the P-wave energy. To avoid mis-interpret weaker reflected P wave as the first P arrival, we perform a second scan without the normalization of the P-wave energy while fixing the S-wave time window from previous scan. Location results on a real event record show the cross-component cross-correlation makes the algorithm work on a wide range of seismic data, and the semblance-weighted stack improves the location resolution.