Advances in acquisition and processing technology help overcome imaging challenges in complex structural settings. The widespread adoption of wide-azimuth (WAZ) and the move towards full-azimuth (FAZ) acquisition geometries, both combined with increasing offsets, result in significantly improved illumination. Reduced compute cost and improved performance enabled reverse time migration (RTM) to emerge as the imaging algorithm of choice in such settings. Of course, an accurate velocity model is a key component in realizing the full potential of these acquisition geometries and algorithms. The trend is towards increasingly more complex anisotropic models, with a move from vertical transverse isotropy (VTI) to tilted transverse isotropy (TTI) and even orthorhombic. In the Gulf of Mexico (GoM), though the importance of defining an accurate anisotropic model in the supra-salt section cannot be understated, the largest contributing factor to a good image subsalt is often the correct delineation of the "salt body" itself. Without an accurate definition of the salt geometry, the subsalt image invariably remains distorted and poorly resolved. In this paper, we will focus on this portion of the depth imaging workflow and illustrate how the techniques of RTM scenario testing and image partitioning can be used in combination to both help define the salt geometry and improve the final post-migration image. We will describe a practical workflow and the key components that we feel are necessary for its success. In addition, we will illustrate a number of lessons learned during the course of recent projects executed in the GoM.

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The remaining potential in many mature fields in the Gulf of Mexico consists of smaller long-reach targets that require ever-more-accurate vertical and horizontal location for drilling precision. This is particularly true at the Lobster field in Ewing Bank, where, during the previous platform drilling campaigns, some midreach prospects were interpreted to have been missed due to mispositioning. Potential future drilling at the Lobster field would target primarily long-reach prospects in areas of significant geologic dip — increasing the risk of missing the prospects. This mispositioning risk could sometimes exceed the geologic risk, and it could have significant impact on the risked reserves and on the economics. Achieving the desired positioning accuracy requires the use of 3D seismic and anisotropic prestack depth migration with accurate velocity and anisotropy models. We have developed a case study of using a long offset walkaway checkshot and a geologic frame of reference to build a tilted transverse isotropy velocity model sufficiently accurate to support potential future drilling campaigns at the Lobster field.