The analysis and interpretation of full waveform sonic data. Part I: dominant phases and shear wave velocity

Borehole sonic logging to determine formation compressional wave slowness has been a routine procedure in the petroleum industry far many years (Summers & Broding 1952; Vogel 1952). However, the digital recording af the full waveforms from these surveys has only become a routine option in the comparatively recent past. Initially, the main motivation for the provision of full waveform sonic logs was the desire to obtain values of shear wave velocity. Nevertheless, the most cursory perusal of these data leads one to conclude that there is a great deal more infonnation to be extracted from the later arriving phases than a simple velocity estimate. This paper describes the interpretatian of full waveform sonic data with examples taken from a wide range of localities around the world. The main emphasis in this paper will be the identification of the principal phases in the microseismogram and the problems associated with the determination of formation shear velocity. In a subsequent paper (Astbury & Worthingtan 1986) other phases, identified as multiples, mode conversions and reflections, will be discussed. All the data presented were recorded with either a Schlumberger Long Spaced Sonic (LSS) sonde or a 1001 designed and operated by 'Société d Études de Mesures et de Maintenance' (SEMM). Both these tools have axially symmetric monopole sources.