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Robert J. Spang1, Michael E. Strickler1, Stephen C. Henry1, Clive G. Sharman2
(1) Texaco Exploration and Production, Inc, New Orleans, LA
(2) Texaco, Ltd, Aberdeen, Scotland

Abstract: Subsalt development at Gemini, deepwater Gulf of Mexico; the role of sequence stratigraphy to "See" the reservoirs

After the drilling of the discovery and subsequent appraisal wells at the deepwater Gemini prospect (Mississippi Canyon block 292), a depositional framework was constructed for development of the subsalt reservoirs. Sequence stratigraphic techniques were used to incorporate biostratigraphic data, post stack time and Chevron-processed pre-stack depth seismic volumes, electric and image logs, sidewall and conventional core, reservoir pressure data, and geochemical data. Pitfalls unique to subsalt seismic imaging include pull-up, multiples, mode converted waves, low frequency content, and as a result, interpretations were worked iteratively between the post stack time and Chevron-processed pre-stack depth volumes. The Gemini salt body currently overhangs the apparent sediment entry point into the Gemini basin. Interpretation of the area outboard of salt, both to the north of and in the Gemini basin were critical to understanding and predicting facies trends. The depositional framework suggested three phases of basin fill: early basin fill characterized by ponded sediment, middle fill characterized by alternating ponding and bypass, and late fill showing bypass. Seismic amplitude maps depict channeling supported with facies analysis of image log and core correlate. The importance of mapping chronostratigraphic surfaces rather than apparent surfaces on seismic was emphasized when amplitude maps on chronostratigraphic surfaces showed more channeling than amplitude maps based on apparent surfaces.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana