Method and apparatus for acoustic dipole direct shear wave well logging

摘要

The shear velocity of a formation traversed by a fluid-filled open or cased borehole is obtained directly. Waveforms are obtained from a dipole acoustic investigation of the formation relative to a common location in the borehole. In this investigation, the bandwidth of the waveforms is substantially bounded by an upper frequency fu at and below which energy traveling at the shear velocity is dominant. Moreover, the bandwidth of the waveforms is concentrated near the frequency fu. The shear velocity of said earth formation is determined from these waveforms. In one embodiment, the waveforms are obtained from a broadband dipole acoustic investigation. The waveforms are low-pass filtered, and an interim shear velocity vs is determined from the filtered waveforms. The filtering and determining of vs are done first for an initial fcut, and subsequently for additional decreasing values of fcut, until a preselected relationship between fcut and vs is satisfied. The last-determined vs is the shear velocity. Other embodiments are discussed.