Patent ID: 7623412

Claim:
A method, comprising: measuring anisotropy of a formation while drilling, the measuring anisotropy while drilling comprising: exciting a dipole wave mode in two orthogonal directions with an LWD tool; receiving and recording in-line and cross-line dipole wave data comprising combined signals resulting from dipole wave propagation through both the formation and the LWD tool; performing an Alford rotation of the combined signals to determine anisotropy of the formation, including identifying fast and slow shear directions of the formation; exciting a monopole wave mode with the LWD tool; receiving monopole wave data and monopole-induced quadrupole wave data resulting from monopole wave propagation through both the formation and the LWD tool; finding orthogonal principal shear directions characterizing anisotropy by observing directions in which received quadrupole wave data has maximum energy; identifying a fast direction of the two orthogonal directions characterizing anisotropy at a negative correlation between monopole and quadrupole received data; and identifying a slow direction of the two orthogonal directions characterizing anisotropy at a positive correlation between the monopole and quadrupole received data.