Azimuthal Seismic Inversion for Shale Gas Reservoir Characterization

Azimuthal AVO analysis can be split into two parts: the Amplitude Versus Offset (AVO) analysis and the Amplitude Versus Azimuth (AVAz) analysis. The properties of the Fourier transform allow these problems to be treated separately. If we calculate a Fourier transform of AVAz PP reflectivity data at a particular angle of incidence, we obtain Fourier Coefficients (FCs) that parsimoniously describe the AVAz and anisotropy, similar to the near offset Rüger equation. It is possible to attach physical significance to each of the FCs using simple rock physics models that relate the anisotropy to the fractures. The different FCs may be combined in a non-linear fashion to estimate fundamental fracture parameters including fracture intensity and orientation. The FCs are calculated using a limited range of offsets or angles, which places less demands on the data acquisition. This may be advantageous for 3D land data sets, where near offsets are particularly under sampled. However, reflectivity-based fracture characterization techniques show some limitations in terms of interpretation of the results. These limitations can be removed by using the azimuthal elastic inversion which provides layer properties that are easier to interpret and relate more directly to the geology.