The primary basins of the Gulf of Mexico form stratigraphically continuous successions on autochthonous salt and therefore contain all the elements of the petroleum system (i.e. source rocks, reservoir intervals, traps, seals). In most of the deepwater northern Gulf the autochthonous salt was deformed during primary basin deposition, initially upward in stocks and walls, and later extruded laterally in a widespread allochthonous salt canopy. As a result, most primary basins are encased either entirely in salt or in some combination of salt and welds. Deepwater Gulf of Mexico exploration is currently focused on targets within primary basins and increasingly on targets at their lateral boundaries. However, because primary basin targets are commonly deep and sub-salt, their boundaries are usually poorly imaged with current seismic technology. Robust structural models are critical to interpreting the structural geometry and evolution of primary basins and to understanding petroleum system implications at their boundaries.

Using modern pre-stack depth-migrated 3-D seismic data, three

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major tectono-stratigraphic provinces that characterize primary basin depocenters have been defined: (1) an immature salt stock canopy province in Mississippi Canyon; (2) a mature salt stock canopy province in northern Atwater Valley, southeastern Green Canyon, Walker Ridge, and southern Keathley Canyon; and (3) an “egg-crate” province comprising a polygonal network of primary basins and deep secondary basins, located in western Green Canyon, Garden Banks, and northern Keathley Canyon.

Six classes of trapping geometry in the primary basins are also recognized: (1) autochthonous salt-cored folds; (2) turtle structures; (3) base-of-salt truncations; (4) salt feeders; (5) salt ridges; and (6) bucket welds. Most primary basin exploration to date has targeted traps in one of the first three styles. Future primary basin exploration will increasingly focus on the traps formed by feeders, bucket welds, and ridges. Each of these features implies a specific, contrasting evolutionary scenario. This in turn has implications for reservoir continuity, charge access, and trap configuration. Of the three primary basin-boundary trap types, salt feeders have the lowest petroleum system risk, followed by bucket welds, and lastly salt ridges with the highest risk.

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