Estimating of fast and slow shear waves

Optimization of hydraulic fracture treatments in tight gas reservoirs requires an in-depth understanding of the reservoir conditions. Elastic properties estimated with standard isotropic amplitude variation with offset (AVO) inversions can offer insight into areas that may be more susceptible to brittle deformation, but do not provide information regarding natural fracture networks or differential stress fields in the rock mass. A more complete characterization therefore requires estimates of anisotropy to account for these phenomena.

Azimuthal AVO inversion makes use of changes in reflection amplitudes with angle and azimuth to extract estimates of anisotropic parameters from seismic data. This case study of the Lower Triassic Montney Formation in NE British Columbia, Canada, showcases an anisotropic extension to the isotropic AVO inversion to include estimates of the fast and slow shear wave velocities. The corresponding ratio of fast and slow shear wave velocities then provides an indication of anisotropy, from which inferences can be made regarding the presence of natural fractures or differential stress fields within the reservoir.