The Tahiti Discovery, announced in April 2002, represents not only a major oil discovery in the deepwater Gulf of Mexico, but also opens an exciting new deepwater exploration frontier in ultra-deep, subsalt reservoirs. The Lower Miocene reservoirs in Tahiti Field are expected be the deepest producing reservoirs in the Gulf of Mexico when first oil arrives through the pipeline in 2008.

The Tahiti Green Canyon 640 #1 well, located in 4,100 feet of water, targeted the hydrocarbon-bearing Lower Miocene section in the emerging Mississippi Fan Fold belt trend, located in south-central Green Canyon (Figure 1). The prospect was located more than 35 miles from the nearest stratigraphic penetration of this interval, and the trend proved to be at a significantly lesser depth than was predicted. The closure tested by the discovery well is a three-way structural nose, trapped against a salt feeder/weld system, buried beneath an 11,000-foot-thick salt canopy. This trap type was considered to be much higher risk than the salt-cored, four-way anticlines previously targeted in the fold belt trend and is very difficult to image on conventional seismic data. Significant stratigraphic risks were also recognized, as pre-drill data were limited.

Figure 1. Location Map of the Tahiti field, GC 640.

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The Tahiti discovery well, spudded in December 2001, successfully confirmed the structural and stratigraphic concepts, encountering more than 400 feet of net oil pay, primarily in three main Miocene turbidite sheet sands at depths ranging from 24,000 to 27,000 feet. Reservoirs penetrated by the well have unusually high quality sands for this depth. Subsequent sidetracking of the discovery and appraisal drilling have confirmed significant hydrocarbon columns of high-quality crude, with excellent reservoir parameters and lateral connectivity (Figure 2). Additional appraisal wells and well tests have resulted in announced recoverable resources of 400 to 500 MMBOE for Tahiti Field.

Future exploratory success for subsalt, ultra-deep reservoirs will need to mirror the successful integration of 3D prestack-depth migration imaging, regional analysis, basin modeling, and prospect scale mapping applied at Tahiti Field. Application of “lessons learned” will be critical, as additional data becomes available in this exciting, but challenging new deepwater frontier.

Figure 2. The Rig Cajun Express Conducts the Tahiti GC 640 Well Test in August 2004.

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