Waveform seismic AVAZ responses from orthorhombic models

Sitamai W. Ajiduah, Gary F. Margrave

A seismic numerical experiment has been conducted with the goal of analyzing the effect of azimuthal anisotropy in HTI and orthorhombic shale models. A set of parallel vertical fractures embedded in a VTI background in shales leads to orthorhombic anisotropy and seismic AVAZ responses. We compute the elastic anisotropy of shales using elastic parameters and based on TIGER elastic finite difference scheme. We calculate AVAZ responses which consist of PP and mode-converted PSV and PSH reflections. Results indicate the AVAZ from the top interface are distinct from those from the bottom, which reveals the presence of propagation effects. Comparisons between HTI and orthorhombic anisotropy for shales indicate the VTI background may alter AVAZ features of reflections. The expected shear-wave splitting behavior is observed in the acquisition domain of X, Y, and Z component but marred by finite difference artificial noise when rotated back to model domain. This posed a challenge in further analysis of the AVAZ behavior of the S1 and S2 signals.