Michael J. DiMarco¹, Gary S. Steffens¹

(1) UNOCAL Deepwater USA, Sugar Land, TX

ABSTRACT: Stratigraphic Studies Associated With The Ultradeepwater Play, Mississippi Fan Foldbelt, Gulf Of Mexico

An important ultradeepwater play is in the early stages of exploration in the Mississippi Fan Foldbelt and its extensions in the Gulf of Mexico. Most of the prospects in this play are anticlinal features with Miocene reservoir targets occurring within the Mississippi Fan foldbelt trend. Many prospects are under a thick allochthonous salt canopy, which compromises their seismic image. Poor seismic imaging beneath the salt makes structural mapping difficult and detailed stratigraphic interpretation nearly impossible. Consequently, our approach to stratigraphic interpretation in support of this deepwater play incorporates (1) regional stratigraphic synthesis of the whole Gulf of Mexico basin, (2) analysis of the sparse well control drilled in the ultradeep to date, and (3) analysis of 3-D surveys on the abyssal plain just outboard of our key subsalt prospect. The Miocene objective section in the subsalt anticlinal prospects extends into the adjacent, relatively undeformed abyssal plain. 3-D seismic surveys shot over the abyssal plain have excellent seismic image quality and good frequency content, making them very amenable to stratigraphic interpretation using isochron, Stratimagic, amplitude extraction and coherency techniques. The results of this comprehensive analysis suggests that the Miocene was a robust sandy depositional system in the Gulf of Mexico, capable of bringing abundant turbidite reservoirs to distal positions hundreds of miles from their coeval deltaic depocenters. These turbidites were dispersed through dip-oriented corridors that can be mapped. There is a general evolution from more sheetlike geometries in the lower Miocene to more channelized and shingled turbidite architectures in the middle and upper Miocene. This evolution in turbidite geometries represents the progressive outbuilding of the overall turbidite system of the Paleo-Mississippi Fan during the Miocene.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado