Borehole sonic measurements are acquired while drilling, on e-line and through the bit using various configuration of transmitters and receivers. The waveforms recorded at receivers from different sources can be analysed distinctly in a slowness frequency dispersion plot for verification of slowness accuracy. Proper dispersion analysis and interpretation requires consideration of many factors such as measurement physics, logging conditions, formation type and knowledge and experience.
The frequency-dispersion plots have proven to be the most robust and reliable method to quality check the data for both dispersive and non-dispersive waves. The other frequently used methods, for example, coherence plot, slowness frequency analysis (SFA) can be considered as complementary. Results from various environments such as borehole washout/rugosity, near wellbore alteration and damage, slow formation, anisotropy, eccentricity effects, and cased hole are captured and analysed. The uncertainty in measured slowness can be introduced by acquisition method, borehole/formation condition and processing parameters. Moreover, this is further propagated to various sonic based solutions. It is an attempt to understand the uncertainty of the available sonic logging technologies from a single reference point i.e. frequency-dispersion plot, instead of going into the details of acquisition and cumbersome processing complexities. In addition to that, the compilation of a wide range of examples from the different borehole and lithologic environment may serve as a standard reference and ready reckoner to demystify the sonic uncertainties in complex logging environments.
