Simultaneous inversion of formation shear-wave anisotropy parameters from cross-dipole acoustic-array waveform data

This study presents an effective technique for obtaining formation azimutha l shear-wave anisotropy parameters from four-component dipole acoustic arra y waveform data. The proposed technique utilizes the splitting of fast and slow principal flexural waves in an anisotropic formation. First, the princ ipal waves are computed from the four-component data using the dipole sourc e orientation with respect to the fast shear-wave polarization azimuth. The n, the fast and slow principal waves are compared for all possible receiver combinations in the receiver array to suppress noise effects. This constru cts an objective function to invert the waveform data for anisotropy estima tes. Finally, the anisotropy and the fast shear azimuth are simultaneously determined by finding the global minimum of the objective function. The wav eform inversion procedure provides a reliable and robust method for obtaini ng formation anisotropy from four-component dipole acoustic logging. Field data examples are used to demonstrate the application and features of the proposed technique. A comparison study using the new and conventional techniques shows that the new technique not only reduces the ambiguity in t he fast azimuth determination but also improves the accuracy of the anisotr opy estimate. Some basic quality indicators of the new technique, along wit h the anisotropy analysis results, are presented to demonstrate the practic al application of the inversion technique.