Determining Microseismic Event Locations by Semblance-weighted Stacking

Summary Estimation of hypocentre locations is a key element of microseismic data processing. In particular, accurate hypocentres are critical for estimating the stimulated reservoir volume. Here, we describe a semi-automated semblance-weighted stacking approach for hypocentre determination that we have developed within matlab. Our current implementation of this procedure is tailored for borehole geophone arrays and is limited to isotropic, horizontally layered media. Event locations are obtained using a 2-D lookup table, computed using an efficient ray-bending algorithm that is robust in the presence of large velocity gradients and strong velocity contrasts at layer boundaries. An interactive procedure is used to scan through the microseismic events and select an approximate time (either P or S arrival) on a single trace. For all depth-distance pairs in the lookup table, semblance-weighted waveform stacks are calculated within P- and S-wave corridors. The location is selected based on the largest semblance-weighted stack value in conjunction with an azimuth determined from energy analysis using horizontal geophones. An advantage of our approach is that the need to obtain accurate P- and S-wave arrival-time picks is eliminated.