Anisotropic Azimuthal Attenuation as an Indicator of Fracture Properties, a Case Study on Time-Lapse Walkaround VSP Data

We derived a formula for azimuthally varying attenuation and provided a method QVOA (seismic quality factor Q versus offset and azimuth) for fracture-direction estimation (o mapping horizontal earth stress) from azimuthally varying attenuation in PP-wave reflection data. The method is illustrated in synthetic data. We introduced a new seismic attribute, the QVO gradient, which can be extracted from 3D wide-azimuth reflection data. QVO-gradient inversion indicates fracture orientation. The magnitude of the QVO-gradient expresses the degree of Q-anisotropy. Q-anisotropy weakly depends on fracture parameters whereas strongly depends on the host-rock Vs-to-Vp-parameter. The QVO-gradient inversion for the fracture parameters is complicated. We believe, that azimuthal QVO analysis (QVOA) can resolve an uncertainty in fracture-direction estimation. Q-anisotropy may be more distinctive than reflection anisotropy, on which azimuthal AVO analysis is based. The QVOA method may have a potential advantage over other approaches because it uses relative characteristics of attenuation and not the absolute ones that are known to be deficient in accuracy.