Azimuthal variation of AVO gradient in fractured reservoirs

The work considers the azimuthal variation of the P-wave AVO gradient at the interface between isotropic medium and<br>transversely isotropic medium with a horizontal symmetry axis (HTI). In particular, the so-called AVO ellipse is<br>investigated, that is AVO gradient variation at different azimuths of the source-receiver line. The goal of the paper is to<br>find out in which cases the orientation of the AVO ellipse coincides with the fracture-strike direction, and in which<br>cases the orientation is perpendicular to the fracture-strike. Numerical modeling of the P-wave reflections was carried<br>out for some reservoir models with different crack infill (gas or liquid) to study AVO ellipse behavior due to sign<br>change of its anisotropic and isotropic parts.