Study of anisotropy evaluation using cross-dipole acoustic LWD

The evaluation of anisotropy is one of the key and difficult points in the study of acoustic logging while drilling(AWLD). In this paper, the finite different method(FDM) is used to simulate the acoustic field excited by the cross-dipole sources in the anisotropic formation. And the flexural waves excited by dipole sources are used to invert the formation anisotropy in the ALWD. The results show that the cross-dipole sources in the HTI formation will stimulate the fast and the slow flexural waves whose velocities are less than these of the fast and the slow shear wave respectively. While using these two flexural waves, we managed to evaluate the anisotropy with a least squares fitting method based on analytic method. Moreover, the transverse direction of the transverse shear wave is obtained by the orthogonal component inversed by the Alford four component method.