Reflections in acoustic borehole logging data can be used to image near-borehole geological structures, either using monopole or dipole measurements, the latter of which resolve azimuthal ambiguity. But accurate tools for wavefield simulation are required to account for wave modes in and out of the borehole, and for the receiver responses to these modes. In this paper, a 3D elastic staggered-grid finite difference method for both isotropic and anisotropic media is discussed in the context of the borehole acoustic imaging problem. Numerical simulation of radiation, reflection and multipole reception of elastic waves, excited by a dipole source, is carried out. In order to optimize azimuthal detection, the relationships between S wave polarization and both source-receiver offset and source-reflector angle are analyzed. Results indicate that the S-S reflection is most sensitive to the angle between the incident ray and the normal to the reflector. Its maximum amplitude occurs as the incident angle reaches critical, a fact that can be used to calculate the total propagation distance of the S-S wave. The critical angle as well as the SH wave velocities of geological structures outside the borehole can thus be determined.
Presentation Date: Thursday, October 20, 2016
Start Time: 9:20:00 AM
Location: 168
Presentation Type: ORAL
