Microseismic waveform and shear‐wave splitting analysis with model data

Abstract

ABSTRACTAccurate and precise estimation of microseismic event location in anisotropic reservoirs is challenging with borehole acquisition, due to limited azimuthal and inclination coverage. Inclusion of shear‐wave splitting information from microseismic data can improve estimates of event directivity, source location and the degree of reservoir anisotropy compared with using P‐waves alone. Additionally, S‐waves typically have a higher signal‐to‐noise ratio than P‐waves, due to higher amplitudes, decreasing the overall azimuthal and depth uncertainty in comparison with P‐wave only location methodologies. We present a joint P‐ and S‐wave hodogram workflow to reduce azimuthal uncertainty and estimate shear‐wave splitting. In this paper, finite‐difference waveform synthetics verify the workflow and illustrate interference effects associated with reflections and head‐waves. Multiple shear‐wave splitting techniques are applied to the synthetic data set in order to understand the limitations between splitting methodologies. Combining the P‐wave hodogram calculation of azimuth and inclination with the shear‐wave splitting analysis lowers the azimuthal uncertainty and improves waveform rotation results. From the comparison of three splitting methods, the minimum second eigenvalue is the most optimum for the data set. Post‐splitting analysis was key as the results are affected by the complexities in the waveforms and arrivals. Using receiver‐by‐receiver splitting quality analysis with shot and receiver clustering improves the identification of quality splitting results.