Quality control of dipole acoustic data

Abstract

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