Rich azimuth marine seismic, a cost effective approach to better subsalt images

There are many areas of complex velocity structure, such as subsalt areas in the Gulf of Mexico, where improvements in depth imaging and noise removal have given better images. However, with several subsalt discoveries, we found some areas where these images are inadequate for cost effective appraisal and development. There have been many cases (some published, for example, O’Connell et al., 1993) where a new seismic survey in a different orientation improves the image in some areas of complex structure, while the image in other areas is better on the original data. These examples suggested that source-receiver azimuth was an important part of the equation. In the spring of 2006, we acquired a rich azimuth survey over our Shenzi discovery (centered on Green Canyon block 653) that took substantially less effort (cost) than we originally imagined. We have presented results at both EAGE and SEG meetings (Howard et al., 2006). This paper documents for a larger audience the studies that led to the decision to conduct the survey and some of those results.