0-000 Approaching Fracture Density: Anisotropic Gradient = Fracture Density?

For optimal hydrocarbon recovery from fractured reservoirs, a critical issue is to gain an accurate understanding of the natural fracture system. Currently, fracture characterization using amplitude based technologies is routinely performed relying on amplitude versus angle/offset (AVA/AVO) and azimuth (AVAZ) to exploit anisotropic gradient behavior, which is today commonly used in the industry as fracture density and is also treated as the principal and proportional cause of anisotropy strength. In using anisotropic gradient as fracture density, except for Rüger conditions we realized that two other implicit assumptions are made: there is a constant pulse earth response, and; there is an equality between measured anisotropic gradient and true degree of anisotropy. In reality earth response is band-limited and exhibits X-Y-T dependence. We will show that these assumptions can lead to dominant artificial effects which may seriously compromise interpretation of seismically derived fracture density.