Abstract:

At present, the research on attenuation anisotropy in media mainly focuses on the case of homogeneous media and pays little attention to the effects of attenuation anisotropy on reflection seismic data. For the viscoelastic anisotropic cap rock/reservoir reflection model, the AVO responses of P-P、P-S waves were investigated for the variation of the Thomsen anisotropy parameters δ、ε of cap rock based on the viscoelastic anisotropic reflection and transmission theory. The anisotropy of phase velocity, quality factor and attenuation were studied, and then, the effect of attenuation anisotropy of the cap rock on AVO analysis was investigated. The study showed that not only phase velocity anisotropy but also attenuation anisotropy exists in viscoelastic anisotropic media. Moreover, the anisotropy degree of the attenuation is much stronger than the phase velocity, and the attenuation anisotropy of S wave is much stronger than that of P wave. When considered only interface reflection, with different anisotropy parameters δ and the variation of critical angles of P-P reflection wave, the reflection coefficients for the pre-and post-critical region would be varied. With the variation of different anisotropy parameters ε, both of the critical angles of P-P reflection wave and the reflection coefficients for pre-critical region nearly do not changed. Because of the attenuation anisotropy of cap rock varied significantly for different Thomsen anisotropy parameters δ、ε, this effect will mislead AVO analysis, and should be compensated before AVO analysis.

Key words: viscoelasticity, anisotropy, AVO response, velocity, attenuation