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

Summary

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.