A blind interpretation of drill-bit signals

The role of kurtosis in evaluating the quality of vertical seismic profilin g (VSP) drill-bit data is investigated. The calculations show how kurtosis depends on the dominant frequency, bandwidth, and phase content of a seismi c signal. This analysis is applied to synthetic and real common-offset and common-shot drill-bit seismograms to evaluate the prominence and quality of the first arrival and other coherent events. High values of kurtosis corre spond to an isolated first arrival or to a compressed coherent noise event, while low values are typical of low S/N (distributed) ratio traces. Kurtos is analysis applied to drill-bit VSP data while drilling proved to be succe ssful at identifying high-quality traces with little interpretational input .