LWD-DATC: Logging-While-Drilling Dipole Shear Anisotropy estimation from Two-Component waveform rotation

Sonic dipole shear anisotropy orientation in subsurface formations is key information for a complete characterization of rock mechanical models for well planning. In Wireline logging, it is estimated with the well-known Alford rotation on four-component inline and crossline waveforms from two orthogonal dipole firings. In contrast, shear orientation estimation is more challenging in Logging-While-Drilling (LWD) operations because of the following reasons:—No exactly orthogonal cross-dipole firings in LWD tools due to tool rotation while drilling;—Coupling between the formation flexural mode and the strong collar flexural mode propagating through the stiff drill collar;—Unavoidable tool eccentering;—Strong drilling noise from vibration, shock, and the turbulent mud flow around the tool; To overcome the aforementioned challenges, this paper describes a new technique to estimate the LWD dipole shear orientation with two-component waveforms obtained from a single dipole firing. It is accomplished by maximizing the projected energy of the two-component waveforms into a subspace defined by two eigenfunctions (the Bessel functions of the first- and second-kinds) accounting for the propagation of the two coupled flexural modes over multiple frequency points. By resorting to the subspace estimation, the new technique has been successfully validated on synthetic data and tested on field data sets.