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GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 45 (1995), Pages 519-528

Chronostratigraphic Hydrocarbon Plays and Depositional Styles in the Northern Gulf of Mexico

Steven Seni (1), Jeff Brooke (2), David Marin (2), Eric Kazanis (2)

ABSTRACT

Sand-body reservoirs in the Federal OCS of the offshore northern Gulf of Mexico were grouped into 98 chronostratigraphic plays by depositional style, structural style, and engineering parameters. Cumulative gas production is apportioned according to three primary depositional styles: progradational (65%), submarine fan (16%), and aggradational (12%). In contrast, cumulative oil production is distributed primarily as progradational (58%), aggradational (23%), and submarine fan (16%). On the continental shelf, progradational environments are hydrocarbon rich owing to favorable sandstone-to-shale ratios and association with salt structures and faulted anticlines. Submarine-fan plays dominate downdip of the modern shelf edge. Remaining recoverable gas reserves for progradational (48%), submarine fan (28%), and aggradational (16%) plays reveal a decline for progradational plays and an increase for submarine-fan plays. Average porosity varies among fan plays (26%), progradational plays (29%), and aggradational or retrogradational plays (28%) (statistical significance, 85-98%), in part as a function of average play depth, which is greatest for submarine-fan plays (3,545 m [11,631 ft]). Average pay thickness of fan (14 m [45 ft]) and retrogradational (10 m [34 ft]) plays is higher than that of aggradational and progradational plays (10 m [31 ft]) (statistical significance, 85-99%).

Proved hydrocarbons are unequally distributed within 16 chronozones in the Gulf. Forty-three percent of the original recoverable oil is concentrated in two chronozones--the lower Pleistocene Lenticulina 1 to Buliminella 1 (22.8%) and upper Miocene Bigenerina A to Cristellaria K (20.4%). Gas is more uniformly distributed. Twenty-nine percent of the original recoverable gas exists in two chronozones--the lower Pleistocene Lenticulina 1 to Valvulina H (18.6%) and upper Pleistocene Hyalinea balthica to Sangamon (10.6%). New discoveries will probably be concentrated in submarine-fan plays in Pleistocene to Miocene strata on the slope and in Miocene and older fan facies on the shelf.


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