Physical modeling and analysis of P‐wave attenuation anisotropy in TI media

Abstract

The amplitudes and frequency content of seismic waves propagating through anisotropic formations may be strongly distorted by directionally dependent attenuation. Here, we analyze physical‐modeling measurements of the P‐wave attenuation coefficient in a transversely isotropic (TI) phenolic sample. Using the spectral‐ratio method, we estimate the group (effective) attenuation coefficient of P‐waves transmitted through the sample for a wide range of propagation angles (from 0° to 90°) with the symmetry axis. Correction for the difference between the group and phase angles is used to obtain the normalized phase attenuation coefficient , which is then inverted for the Thomsen‐style attenuation‐anisotropy parameters and . Whereas the symmetry axes of the angle‐dependent coefficient A and of the velocity function have close orientations, the magnitude of the attenuation anisotropy far exceeds that of the velocity anisotropy. The quality factor increases more than tenfold from the symmetry (slow) direction to the isotropy plane (fast direction). The robustness of our results depends critically on several factors, such as the availability of an accurate anisotropic velocity model and the adequacy of the “homogeneous” concept of wave propagation. The methodology discussed here can be extended to field measurements of anisotropic attenuation needed for AVO (amplitude variation with offset) analysis and seismic fracture detection.