Numerical Modeling of P-wave AVOA in Media Containing Vertical Fractures

This paper investigates the use of seismic anisotropy and amplitude variation with offset and azimuth (AVOA) for fracture characterization. The paper looks at P to P-wave reflectivity at the interface between an isotropic half-space overlying a transversely isotropic half-space with a horizontal symmetry axis (HTI medium). The reflecting HTI medium is chosen to be long wave equivalent a medium with aligned vertical cracks (a single crack orientation) in an isotropic host rock. Azimuthal variation of AVO gradient is investigated for the three models: with fluid-filled cracks, with dry cracks and for the case of saturated cracks in an porous host rock — in different situations of changes in the elastic parameters in the upper and lower media. It is shown that P-P AVOA holds significant information about fracturing but potential ambiguity in the interpretation of these data is observed that could lead to incorrect determination of fracture infill (gas o water) and fracture orientation.