A comparison of LWD and wireline dipole sonic data

Abstract

Data measured by both wireline and LWD tools in the same borehole are compared. Discrepancies in shear velocities as calculated from the data are on average around 5% and discrepancies between compressional velocities are less than 3%. The consistency of the bias between logs suggest it is related to the calculation of velocity. Comparison of industry and ERL velocity processing show excellent agreement and give an example of possible spread of velocity data due to processing chain. A short section of data in an unconsolidated zone shows velocity differences of just over 10% with an opposite trend to the over all bias. Dispersion analysis of the waveforms show this is consistent with a damaged zone surrounding the borehole wall caused by drilling.