Dispersion Corrections Are Not Just for LWD Dipole Sonic Tools
Jennifer Market, Wyatt Canady · 2006
Many studies have been published showing dispersion characteristics for borehole sonic data, particularly for dipole wireline and dipole and quadrupole LWD tools. With the exception of LWD dipole tools, however, the dispersion corrections are often ignored. It is commonplace for the wireline flexural velocity to be used as the shear velocity. This substitution may be acceptable practice when dispersion correction is less than 2%. There are many cases, however, when the dispersion correction exceeds this amount and correction is necessary. The dispersion behaviour is dependent on formation properties, hole size and mud properties. There are tools issues as well - particularly the complex interaction between the resonant frequency of the formation and the frequency response of the acoustic source. Acoustic tools based on broadband sources are particularly susceptible to dispersion induced inaccuracies. For that reason, a properly implemented quality analysis program is critical to ensuring accurate shear velocity measurement.