Subsalt depth imaging issues, techniques, and results from the Mississippi Canyon Area of the Central Deepwater Gulf of Mexico

Abstract

SUMMARY Successful prestack depth imaging of subsalt structures has added significant value to the exploration business in the Central Gulf of Mexico. Subsalt prospects within these areas have been difficult to image seismically. Because of the complex geometries of the salt and approximate 2:1 contrast in velocity relative to the surrounding sediments, prestack depth imaging is required for successful delineation of subsalt prospect structural geometries and quantification of reserve potential. We show that the value of subsalt prestack depth imaging is developed through special attention to specific elements of the imaging process. Prestack depth imaging is a very accurate process and its success in subsalt areas demands high precision velocity models and careful pre-processing of the data to preserve primary energy. Steep salt flanks and stacked salt sheets can complicate the estimation of the velocity model. The inherent 3-D nature of multiples requires a sophisticated approach for removal. Even though mode conversions are harder to spatially describe, they can be partially attacked by 2-D processing techniques. Understanding the imaging limitations can help define different strategies for acquisition, processing, and interpretation. By mapping multiples on depth data and generating illumination maps we can better understand the resultant depth images. A compilation of results from a variety of subsalt exploration prospects will be shown to illustrate our approach and demonstrate the business impact of our work.