ABSTRACT

The petroleum geology of the Mississippi Canyon, Atwater Valley, western DeSoto Canyon, and western Lloyd Ridge protraction areas, offshore northern Gulf of Mexico, is controlled by the interaction of salt tectonics and high sedimentation rate during the Neogene and resulted in a complex distribution of reservoirs and traps. We evaluate 87 fields and discoveries: 51 with combined structural/stratigraphic traps (three-way closures), 19 with structural traps (four-way closures), and 17 with stratigraphic traps. Three of these discoveries are in Upper Jurassic eolian reservoirs; the remaining discoveries are in Neogene deep-water reservoirs.

The tectono-stratigraphic evolution of the area is analyzed at 11 discrete intervals between 24 Ma and the present. Four stratigraphic external forms—troughs, bowls, wedges, and sheets—are integrated with the structural geology to understand the changing shape of subbasins and minibasins, primarily in a slope setting. This analysis shows how the allochthonous salt systems evolved over time and how salt movement affected sedimentation patterns and subbasin evolution.

The study area includes some of the largest fields in the northern deep-water Gulf of Mexico, such as the Thunder Horse field, which produces from an anticlinal (turtle) structure, or the Mars–Ursa and associated fields with greater than 1.5 billion BOE estimated ultimate recovery, which developed with a counterregional allochthonous salt system. The remaining fields have considerably smaller reserves, which are controlled by the area within closure and the number of reservoir intervals.

Most of fields in the study area are contained within sheet-shaped or wedge-shaped stratigraphic external forms and have four-way or three-way trapping configurations. These findings indicate the profound effect of mobile salt on the petroleum geology of the region.

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