Primary Basin Boundaries in the Gulf of Mexico: Three Hydrocarbon Trap Types with Distinct Petroleum Systems Implications
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 (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 extruding laterally in an extensive 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 basins targets are commonly deep and sub-salt, their boundaries are, more often than not, poorly imaged with current seismic technology. Robust structural models are critical to interpreting the structural geometry and evolution of primary basin as well as understanding the petroleum systems implications at their boundaries.
With modern pre-stack depth migrated 3-D seismic data we have defined three major tectono-stratigraphic provinces that characterize primary basin depocenters: (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.
We also recognize six classes of trapping geometry in the primary basins: (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 imply a specific, contrasting evolutionary scenario, which 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, with salt ridges having the highest risk.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009