Cenozoic Deep-Water Reservoir Systems of the Northern Gulf of Mexico Basin

By

GALLOWAY, WILLIAM E.

John A. and Katherine G. Jackson School of Geosciences, The University of Texas, Austin, TX

The Cenozoic sedimentary fill of the northern Gulf of Mexico (GOM) basin contains thick, reservoir-rich successions deposited in both constructional and destructional slope systems. Slope and base-of-slope sand bodies are principal objectives of deep-burial, sub-salt, and deep-water plays that dominate recent GOM exploration. Turbidite channel fill, lobe, and sheet deposits constitute the reservoir facies within both kinds of systems. Constructional slopes were dominated by deposition of allochthonous sediment and include delta-fed and shelf-fed slope apron and submarine fan systems. Regional offlap architecture characterizes constructional slopes. Syndepositional deformation of salt and shale substrates created dynamic and complex slope morphologies. Both salt evacuation and fault displacement formed intraslope basins that filled with stacked, uplapping successions of slope facies. Repeated “fill and spill” episodes characterize these intraslope basins. Destructional slope systems record local to subregional shelf margin and upper slope retreat with consequent development of a significant bounding surface (composite slide plane, canyon-cut surface, or regional mass-wasting surface). Recycled autochthonous upper slope sediment forms a lower slope debris apron. Though of secondary volumetric importance in the GOM, destructional slopes create highly productive reservoir systems in autochthonous apron, submarine canyon fill, and megaslide deposits. Further, large submarine fan systems commonly originate at sites of slope destruction.

The Pliocene Globoquadrina altispira (PGa) genetic sequence contains productive examples of both constructional and destructional slope reservoir associations. Distinctive exploration plays are created by slope sand facies contained within each of these slope system types. A large submarine fan system awaits drilling on the Gulf abyssal plain.