4:45 PM - 5:00 PM
[STT55-12] Estimation of Shear wave anisotropy of Transeversely Isotropic medium by Full Waveform Inversion
Keywords:Anisotropy, Full Waveform Inversion, Borehole Geophysics
In this research, a numerical experiment is conducted on the sonic logging model which contains the anisotropic layer. A cross dipole, which consists of two orthogonal dipole sources, is used as a transmitter. For the anisotropic model, a transversely isotropic medium with a horizontal axis of symmetry with five independent elastic elements is set. According to previous studies, it is suggested that the received waveform obtained by the cross dipole measurement changes with the degree of anisotropy of the rock. Distinctive feature can be observed when shear wave passes through the anisotropic layer and splits into two polarized waves: fast shear and slow shear. We attempt to estimate the elastic parameters using the shear waves. Full waveform inversion (FWI) is applied to estimate the elastic parameters directly. FWI is one of the techniques to estimate the ground physical properties with high accuracy and resolution by updating the model parameters so as to minimize the residual between the observed and the calculated waveforms. As a result, it was suggested that highly accurate estimation of elastic parameters is achieved by applying FWI to the layer where anisotropy exists. Although the resolution depends on the receiver interval in conventional slowness time coherence method, it is suggested that FWI can estimate ground physical properties with high resolution.