Abstract
Abstract
In slow formations borehole acoustic Logging While Drilling (LWD) operations, it is common to obtain formation shear slowness from the dispersive borehole quadrupole wave. Due to poor signal to noise ratio and/or tool eccentricity effects, it is not always possible to obtain formation shear slowness directly via conventional Slowness-Time-Coherency (STC) methods. Consequently, a dispersion correction is frequently needed to QC and/or correct the STC result. We propose a hybrid method that allows for a model-based (MB) as well as a phenomenon-based (PB) approach. The latter is ideally suited to address, identify, and overcome the limitations and dependence of the former, on tool eccentricity, tool model, inaccurate knowledge of borehole fluid slowness, formation anisotropy (Vertical Transverse Isotropy), and other unknown acquisition circumstances.