Tilted Orthorhombic Imaging for full Azimuth Towed Streamer Data in Deep Water Gulf of Mexico
Yunfeng (Fred) Li
Compared with isotropic and vertical transverse isotropic (VTI) imaging, tilted transverse isotropic (TTI) prestack depth imaging generally provides flatter common image gathers (CIGs) for wide azimuth (WAZ) data, improves image focusing, and significantly reduces well/seismic mis-ties. However, the presence of significant tectonic stress or uneven stress can cause fractures in thin-bed layers, which results in a directional velocity variation for seismic wave propagation, or azimuthal anisotropy. In these cases, TTI assumption is insufficient to explain conflicting residual moveouts among CIGs of different azimuths from TTI imaging. A more general anisotropic model, tilted orthorhombic (T-ORT), is needed to cope with azimuthal velocity variation in these complex geological settings. Instead of five parameters as in a TTI model, a T-ORT model has nine parameters. Deriving a set of reliable T-ORT parameters is a challenging task. Recently, ray tracing, Kirchhoff and beam migration, and Reverse Time migration (RTM) have been developed to handle T-ORT anisotropy. And full-azimuth (FAZ) data has been acquired in the deep water blocks in the GOM and provides abundant azimuthal information for deriving the parameters of a tilted orthorhombic model. This paper focuses on the key components of T-ORT depth imaging: the procedure to build initial T-ORT models and T-ORT tomography. With a real FAZ dataset in the GOM, we demonstrate the effectiveness of the T-ORT velocity model building, where the estimated T-ORT anisotropic parameters are consistent with the geological setting. T-ORT prestack depth migration flattens common image gathers (CIGs) in all azimuths and results in improvements in image focusing, as well as spatial positioning of complex structures.
AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013