We present a case study of anisotropic model building and the resulting accuracy of event placement and improved image quality. Approximately 660 OCS blocks of the MC Revival survey located in Mississippi Canyon area were imaged using anisotropic Kirchhoff pre-stack depth migration (Figure 1). The goals of this large scale project were accurate event placement and improved imaging of steep dips, salt boundaries, and subsalt events. To accomplish these goals, all available well information was used to calibrate the seismic velocity model from prior isotropic pre-stack WEM imaging. The resulting vertical velocity model was used to generate isotropic PSDM image gathers for use in determination of the anisotropy parameters epsilon and delta. These fields were derived from an automated two-parameter residual curvature analysis. Multiple iterations of migration for picking salt overhangs were a necessity to properly image salt bases and subsalt events. Focusing of events was enhanced through iterations of tomography both supra and subsalt. We achieved significant improvements in defining the salt boundaries and in positioning the reflectors and salt overhangs by properly accounting for the effect of anisotropy.

The Hoop Fault complex in the Southwestern Barents Sea presents an imaging challenge to accurately model the sharp velocity contrast across a major fault boundary. Improperly accounting for this velocity discontinuity would lead a poorly focused image and false structures. We present an approach that leverages interpreted fault planes as well as marker horizons to drive and constrain tomographic velocity updates.

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We present a case study of enhanced imaging of wideazimuth data from the Gulf of Mexico utilizing recent technologies; and we discuss the resulting improvements in image quality, especially in subsalt areas, relative to prior methodologies. The input seismic data set is taken from the large scale Freedom WAZ survey located in the Mississippi Canyon and Atwater Valley areas. In the course of developing the enhanced wide-azimuth processing flow, the following three key steps are found to have the most impact for improved subsalt imaging. 1) Data regularization to prepare the data for multiple attenuation as well as for the final run of anisotropic reverse time migration; 2) 3D true azimuth SRME to remove multiple energy, in particular, complex multiples beneath salt; 3) reverse time migration based delayed imaging time (DIT) scan to update the complex subsalt velocity model. The DIT scan further improves the accuracy of the subsalt velocity model after the conventional ray-based subsalt tomography. In this paper, we focus on the depth imaging aspects of the project, with particular emphasis on the application of the DIT scanning technique. We also demonstrate the uplift of acquiring a wide-azimuth data set relative to a standard narrowazimuth (NAZ) data set.

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