A subsurface section, much simplified, showing the deepwater play beneath the salt layers is illustrated in this article, which outlines the great size of the prospective fields.

The article is generalized, but I no longer subscribe to the technical journals that would contain more detail.

Prospectivity of the Ultra-Deepwater Gulf of Mexico, Anderson and Boulanger, Lamont-Doherty Earth Observatory, Columbia University.
Some of the difficulties in designing drilling for this realm are discussed.

http://leanenergy.Ideo.columbia.edu/docs/UltraDeep%20Prosp%2010-22-02.pdf