A Dispersion-based Approach for Monopole Slowness Estimation and its Implications for Borehole Geology

Monopole acoustic logging is one of the most common approaches to evaluate borehole geology conditions. It is recognized that overlapped waves or wave interferences in monopole waveforms can pose a practical challenge to reasonable geological interpretations. To mitigate this situation, this paper presents a method to extract and reconstruct the waveforms of interest (i.e., compressional, shear and Stoneley wave) from the original waveform data by using Radon transform. In particular, an adaptive muting scheme is employed to overcome the severely diffused energies caused by the limited receiver samplings, which is an intrinsic issue of borehole acoustic logging. Then, a new slowness spectrum is formulated via a dispersive perspective to upgrade the accuracy of slowness estimation. In practice, the entire workflow is demonstrated by a high- frequency monopole example, and the derived results suggest that wave separation is a critical step to reveal true kinematic and dynamic behaviours of each wave mode prior to interpretation. Moreover, it is shown that using the adopted dispersive measure to analyse borehole compressional and shear waves can remarkably enhance the accuracy of slowness estimation with respect to borehole geology.