EFFECTS OF ATTENUATION AND ANISOTROPY ON REFLECTION AMPLITUDE VERSUS OFFSET

To investigate the effects that attenuation and anisotropy have on ref lection coefficients, we consider a homogeneous and viscoelastic wave incident on an interface between two transversely isotropic and lossy media with the symmetry axis perpendicular to the interface, Analysis of PP and PS reflection coefficients shows that anisotropy should be t aken into account in amplitude Variation with offset (AVO) studies inv olving shales. Different anisotropic characteristics may reverse the r eflection trend and substantially influence the position of the critic al angle versus offset. The analysis of a shale-chalk interface indica tes that when the critical distance is close to the near offsets, the AVO response is substantially affected by the presence of dissipation. In a second example, we compute reflection coefficients and synthetic seismograms for a limestone/black shale interface with different rheo logical properties of the underlying shale. This case shows reversal o f the reflection trend with increasing offset and compensation between the anisotropic and anelastic effects.