BOREHOLE WAVE-PROPAGATION IN 3 DIMENSIONS

In this paper the three-dimensional finite difference method is used to simulate borehole wave propagations in an isotropic as well as an anisotropic formation. The finite difference results agree excellently with the analytic solutions of a point force source in the transversely isotropic medium. The finite difference synthetics are also in very good agreement with the discrete wave-number solutions for fluid-filled borehole wave propagation. The finite difference synthetics are compared with ultrasonic lab measurements in a scaled borehole model. The borehole is drilled along the X axis in an orthorhombic phenolite solid. Both monopole and dipole logs agree well. The observations of the shear wave splitting in the dipole logs, are confirmed by the finite difference simulations. The 3-D finite difference method is applied to the fluid-filled borehole wave propagation in the tilted isotropic formation and in the orthorhombic phenolite formation. In a borehole drilled along the Z axis in a phenolite formation, the monopole log shows the P wave traveling with velocity vzz. There are no shear-pseudo-Rayleigh wave arrivals. The dipole log is dominated by the single slow flexural mode. In a borehole drilled along the Y axis in a phenolite formation, the monopole log shows the P wave traveling with velocity vyy. There are shear-pseudo-Rayleigh wave arrivals shown on the monopole seismograms between P and Stoneley waves due to the shear wave anisotropy. The anisotropy also causes the shear wave splitting in the dipole log. The two shear wave arrivals correspond to the fast and the slow flexural modes. © 1995, Acoustical Society of America. All rights reserved.