Uncovering Seismic HTI Anisotropy of the Cooper Basin

Abstract

3D seismic data from the Cooper Basin exhibit horizontal transverse isotropy (HTI) anisotropy in amplitude versus offset (AVO) and interval migration velocity. Theoretically, vertical fractures and in-situ stress can induce HTI anisotropy. The main objective is to determine if the HTI anisotropy is caused by fractures or by the Cooper Basin’s large difference between minimum and maximum horizontal stress. We compare migration velocity anisotropy and seismic AVO anisotropy extracted from a high-quality 3D survey with a “ground truth” of dipole sonic logs, borehole breakout, and fractures interpreted from image logs. The AVO anisotropy is inverted using Rüger AVO algorithm and Fourier Coefficient algorithm that give similar results. Fractures interpreted from image logs are primarily oriented approximately 30° from SH.

Our work suggests that stress is the dominant cause of the HTI anisotropy observed in the seismic data. The fact that seismic anisotropy is parallel with current SH and not aligned with the observed fractures suggests that Cooper Basin large differential stress causes the anisotropy observed on seismic.