Quality control of dipole acoustic data

Abstract

Wave form excited by an acoustic dipole source in theory should consist of flexural waves only. Unfortunately usually it is contaminated by other acoustic modes including Stoneley, compressional wave and ringing casing. These undesired modes depend on the tool position inside the borehole, well deviation and its size, and presence of casing. Unwanted wave forms might be additionally augmented by poorly balanced dipole source and/or receivers. The classic semblance processing method will routinely deliver good looking results even when there are problems with one or more acoustic receivers and/or with poorly chosen processing parameters. Therefore I propose to add a complex wave form analysis as an additional quality control measure and to cross check the semblance method. Ways to identify a mixed acoustic mode condition and to eliminate biases in the shear slowness curves will be described. I also show how to qualify cross dipole data needed to perform shear wave anisotropy analysis.