The last days of 2005 brought an announcement from Chevron and its partners that a Gulf of Mexico wildcat they drilled to record depths was a standout discovery. The #1 (BP2) OCS-G-26315 tested the Knotty Head prospect in Green Canyon 512. The well was drilled in 3,570 feet of water by Transocean's Discoverer Spirit drillship. On its way to a total measured depth of 34,189 feet, a Gulf of Mexico record, the well intersected some 600 feet of net oil pay in multiple zones. Fluid samples and conventional and sidewall cores indicated that high-quality oil and high-quality reservoir sands were present. Interests in Green Canyon 512 are held one-quarter each by Calgary-based Nexen Inc., Houston-based Anadarko Petroleum Corp., Australian firm BHP Billiton and Chevron Corp. Nexen operates the block, although Chevron drilled the initial well. The partners are now drilling a sidetrack appraisal well, and plan additional appraisal work this year to assess the size of the discovery. The group won the block in OCS Sale 190 held in March 2004 with a bid of $31 million, one of the highest bids made in that offering. Knotty Head initially made the news in mid-2005 when it had reached 29,670 feet and had already encountered 300 feet of apparent pay in secondary objectives. With the addition of another 300 feet of net pay in the deeper portion of the hole, Knotty Head has now catapulted into the top tier of Gulf of Mexico discoveries. Potential reserves are speculated to be in the range of 300- to 500 million barrels of oil. The Knotty Head test targeted a large four-way closure in southern Green Canyon in the deepwater Mississippi Fan Foldbelt province, one of the Gulf of Mexico's hot exploratory areas. The combination of gigantic structures, high-quality turbidite reservoirs and rich source rocks make this trend quite alluring to the industry's premier players. However, about 80% of the Mississippi Fan Foldbelt lies below the Sigsbee salt canopy, which obscures seismic and makes geophysical prospecting extremely challenging. The ultradeep, subsalt play was opened by the discovery of Tahiti, a 400- to 500-million-barrel find that Chevron drilled in 2002. Knotty Head lies 15 miles northeast of Tahiti. Tahiti was drilled in 4,017 feet of water to a depth of 28,411 feet on Green Canyon 640. It was a major wildcat, more than 30 miles from the nearest Lower Miocene penetration, and its target sands were at considerably greater depths. The gamble paid off: after the discovery well penetrated 11,000 feet of salt, it encountered more than 400 feet of oil pay in sands at depths between 24,000 and 27,000 feet. The #1 OCS-G-20082 was completed last September at a depth of 25,812 feet, making it the deepest successful well in the Gulf. It was tested at a rate of more than 15,000 barrels of oil per day. In a fast-track approach to development, Chevron simultaneously drilled two appraisal wells on Tahiti. One well cut more than 1,000 feet of net pay, one of the best totals yet encountered in the Gulf. This past fall, Chevron and its partners Statoil and Shell started construction of the floating production facility for the field. First oil is expected in mid-2008, and daily production capacity will be 125,000 barrels of oil and 70 million cubic feet of gas. The group expects to spend $3.5 billion on the project. Certainly, the engineering hurdles that must be overcome in the phenomenally deep and highly pressured reservoirs are steep. New technologies are rapidly being developed for completion, testing and production of such prolific subsea wells in such extreme conditions. Other companies are eager to explore in this new El Dorado. Already, another test is under way a mile northeast of Knotty Head. Amerada Hess is drilling its Pony prospect in Green Canyon 468. The #1 OCS-G-26313 was spudded in November 2005 by Diamond Offshore's Ocean Baroness semisubmersible. The well is in 3,440 feet of water and is projected to a depth of 32,000 feet. New York-based Hess picked up the block in OCS Sale 190 for $35 million, the highest bid of the sale. It bested four other contenders for the tract, according to IHS Energy.