Wave field simulation on 3D borehole dipole radiation

Junxiao Li, Kristopher A. Innanen, Kuo Zhang, Guo Tao, Laurence R. Lines

Wave simulation in borehole environment is crucial for characterization of the waveforms traveling through the borehole, recorded by the receivers, leaking away outside borehole and reflecting from geological structures outside borehole. In order to mitigate this directional ambiguity, a dipole acoustic reflection imaging is developed. In this paper, a 3D elastic staggered-grid finite difference method for both isotropic and anisotropic media is discussed for the bore hole acoustic wave simulation. A hybrid perfectly matched layer is proposed which removes the artificial reflections from the computational regions. A numerical simulation of radiation, reflection and multipole reception of the elastic waves in the presence of a dipole source is proposed, for azimuthal detection, to characterizing the relationship between S wave polarization and the offset between the source and receivers as well as the angle of the source and reflector. The results show the amplitude change of S-S reflection is related to the incident angle to the reflector. Its maximum amplitude occurs as the incident angle reaches to a critical angle, which can then be used to calculate the total propagation distance of the S-S wave. As a result, the critical angle as well as the SH wave velocity of the second layer outside the bore hole can thus be determined.