TTI Tomography for Dual-Azimuth Data in Gulf of Mexico

Over the past decade, the majority of deep water blocks in the Gulf of Mexico have been covered multiple times with seismic data from narrow-azimuth, towed-streamer acquisition (NAZ). In complex subsalt areas, each NAZ dataset provides unique subsurface illumination benefits. Multiple-azimuth data are now frequently integrated to provide extended subsurface coverage and for better imaging of complex subsalt structures. Multiple-azimuth seismic data, with shot and receiver locations covering a large portion of the two dimensional surface, presents a new challenge for deriving a single velocity model that satisfies both datasets.

In exploration and development work in Deep Water Gulf of Mexico, there has been an increasing demand to incorporate anisotropy in prestack depth imaging workflows. Incorporating anisotropy improves image quality and well/seismic miss-ties. While most pre-stack depth imaging involves VTI anisotropy, transverse isotropy with tilted symmetry axis (TTI) is generally overlooked. Shale layering near steeply-dipping salt flanks can cause TTI anisotropy issues. In such a case, ignoring the tilted symmetry of salt flank bedding causes image blurring and mis-positioning of the salt flank structure. Velocity variation with azimuth is observed in an orthogonal dual-azimuth streamer dataset, as well as wide-azimuth data in Deep Water Gulf of Mexico. The paper presents a study to build a single TTI anisotropy model for prestack depth imaging of dual-azimuth data in Deep Water Gulf of Mexico, to yield an anisotropy model that flattens gathers for all azimuths as well as improves focusing and spatial positioning of steeply-dipping salt flanks.