Seismic anisotropy in dipping shales causes imaging and positioning problems for underlying structures. We developed an anisotropic depth‐migration approach for P-wave seismic data in transversely isotropic (TI) media with a tilted axis of symmetry normal to bedding. We added anisotropic and dip parameters to the depth‐imaging velocity model and used prestack depth‐migrated image gathers in a diagnostic manner to refine the anisotropic velocity model. The apparent position of structures below dipping anisotropic overburden changes considerably between isotropic and anisotropic migrations. The ray‐tracing algorithm used in a 2-D prestack Kirchhoff depth migration was modified to calculate traveltimes in the presence of TI media with a tilted symmetry axis. The resulting anisotropic depth‐migration algorithm was applied to physical‐model seismic data and field seismic data from the Canadian Rocky Mountain Thrust and Fold Belt. The anisotropic depth migrations offer significant improvements in positioning and reflector continuity over those obtained using isotropic algorithms.
Principal stresses, that is vertical, maximum horizontal and minimum horizontal stresses, and elastic moduli related to rock brittleness, like Young's modulus and Poisson's ratio, can be estimated from wide-angle, wide-azimuth seismic data. This is established using a small 3D seismic survey over the Colorado shale gas play of Alberta, Canada. It is shown that this information can be used to optimize the placement and direction of horizontal wells and hydraulic fracture stimulations.
A case study of the acquisition of a high-density, broadbandwidth vibroseis survey on Alaska's North Slope, using a high-productivity slip-sweep technique, shows the merits of this technique for acquisition of high-density data in a short time frame in extreme conditions as well as the benefits of high-density broadband data for subsequent processing, imaging, and seismic inversion.
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