Mesoscopic attenuation mechanism in VTI seismic anisotropy

Abstract

In this work, the effect of mesoscopic heterogeneity in the attenuation and scattering of waves propagating in poroelastic media is studied analytically and numerically. In case of heterogeneity size lower than the dominant wavelength, the medium composed of interbedded poroelastic layers of different lithology or by layers saturated with different fluids behaves as a homogeneous VTI medium. We developed frequency dependent expressions to estimate attenuation and phase velocity in such media. The results indicate that the behavior of the slow and fast compression waves depend on the frequency and direction of propagation. When an wave propagates parallel to the symmetry axis, attenuation of the rapid P wave becomes highest while the attenuation of the slow P wave becomes lowest. The behavior of the acoustic waves confirms that the slow P wave responds to the fluid flow associated with heterogeneities that generate pressure gradients on the borders that separate poroelastic media. The wave propagating in all directions manifests the mesoscopic mechanism at low frequency and the Biot's one at high ones. The dominant mechanism depends on the path of propagation and the degree of heterogeneity of the poroelastic compound.