Patent ID: 7310285
Filing Date: 2007-12-18
Classification: G01V

Abstract:
1. A method of characterizing shear wave anisotropy in a formation, comprising: obtaining crossed-dipole waveforms from a borehole penetrating the formation over a range of depths and frequencies; determining far-field slowness in a fast-shear and slow-shear direction using a low-frequency portion of the crossed-dipole waveforms; determining near-wellbore slowness in the fast-shear and slow-shear directions using a high-frequency portion of the crossed-dipole waveforms; marking a selected depth of the formation as having intrinsic anisotropy if at the selected depth the far-field slowness in the fast-shear direction is less than the far-field slowness in the slow-shear direction and the near-wellbore slowness in the fast-shear direction is less than the near-wellbore slowness in the slow-shear direction; and marking a selected depth of the formation as having stress-induced anisotropy if at the selected depth the far-field slowness in the fast-shear direction is less than the far-field slowness in the slow-shear direction and the near-wellbore slowness in the fast-shear direction is greater than the near-wellbore slowness in the slow-shear direction.