A full waveform inversion method for inverting S-wave velocity profiles of slow formations near borehole

The borehole full waveform inversion (BFWI) method represents a novel approach for inverting S-wave velocities in slow formations by utilizing the comprehensive information available from acoustic logging waveforms. This method stands out from traditional techniques, which are limited to formations with uniform velocity within the axial resolution of the logging tool or where the radial distribution pattern of S-wave velocity is already known, and which only make use of a subset of the acoustic waveform data. The BFWI method iteratively enhances the model to align the inverted waveforms with the actual waveforms by leveraging the full waveform information, including both guided and critically refracted waves. This comprehensive use of data significantly improves the precision and reliability of estimating S-wave velocities in slow formations. The method’s effectiveness has been demonstrated through tests on thin-multilayer and alteration-zone models, showing that BFWI can accurately depict the S-wave velocity profiles in both wireline logging and logging-while-drilling scenarios. Moreover, within ultra-slow formations, BFWI not only accurately inverts the S-wave velocity profile but also retrieves the P-wave velocity with high precision, even in the presence of interfering leakage P-waves. This advancement offers a robust tool for the more precise measurement of S-wave velocity profiles in slow formations, potentially enhancing the accuracy of subsurface characterization in the petroleum industry.