An analysis for unipole acoustic logging while drilling wavefields with varying eccentered collar positions

Abstract The unipole logging while drilling (LWD) tool is a recently developed acoustic that uses an azimuthal emitting source to generate waves in the borehole measure longitudinal and transverse wave speeds of surrounding stratum. In this study, transmitter transducer modeled as surface force source, analytical solution for LWD wavefield derived. received waveforms are composed infinite-order contributions owing directivity excitation source. Using up eight lowest-order modes, excited by calculated both soft hard formations, then slowness-time coherence velocity dispersion analysis performed. pure mode obtained using decomposition method. influence eccentricity (off-center positioning) on wavefields also discussed. Based addition theorem Bessel function, when eccentered can be obtained. with eccentricities 0 90% compared. Tool has smaller effect formation than formation. side closest wall affected most off center, sharp increase amplitude fast late arrival group These conclusions important design data interpretation tool.