Method for determining earth formation shear wave anisotropy parameters by inversion processing of signals from a multiple-component dipole array acoustic well logging instrument

摘要

A method for determining orientations and velocities of slow and fast waves in an anisotropic earth formation. Signals are used from an acoustic logging tool including dipole transmitters and receiver arrays. An initial value of angle subtended between orientation of the fast wave and one of the transmitters is selected. A waveform of a fast principal wave and slow principal wave at first and second selected receiver positions are calculated from received signals at each of these positions and the selected subtended angle. A derivative waveform with respect to subtended angle is calculated for both fast and slow principal waves. An initial velocity of slow waves is selected and the calculated waveforms of the slow principal wave and its derivative waveform at the first position are time shifted by a time corresponding to distance between first and second receiver positions and the selected value of velocity. A value of difference in velocity between slow waves and fast waves is selected, and the time-shifted slow principal wave and its derivative waveform are adjusted by a time corresponding to the value of difference in velocities. Differences between the time-adjusted wave and its derivative waveform are determined between the calculated fast principal wave and its derivative waveform calculated at that receiver position. The value of velocity, value of difference in velocity and subtended angle are adjusted and calculating waveforms and derivative waveforms, time shifting and time adjusting are repeated until the difference between waveforms reaches a minimum.