Estimation of Interval Velocity and Attenuation Anisotropy from Reflection Data at the Coronation Field

Attenuation can be extremely valuable in characterizing gas accumulations in shales and sands. In fractured reservoirs, anisotropy can provide additional information about the distribution of fractures. Here, we apply a layer-stripping approach to wide-azimuth P-wave data acquired over a gas reservoir in the Coronation Field, Alberta. The main processing steps involve estimation of traveltimes from the top and bottom of the target layer followed by computation of the interval NMO velocity and attenuation coefficients using velocity-independent layer stripping and the spectral-ratio method. The vertical attenuation coefficient shows a reasonable correlation with existing gas-producing well locations, and, therefore, serves as an indicator of gas accumulation in pore space. Based on the attenuation information, we conclude that the lower half of the survey area has significant gas reserves. In these areas, the estimated azimuthal velocity anisotropy can be used to plan horizontal wells oriented orthogonal to the fracture direction.