Operator to Wield Double-Duty Floating Rig in Gulf

BP chooses GlobalSantaFe's Development Driller ll to both drill and complete some 20 subsea wells at its deepwater Atlantis project beginning in July 2005. Bold move could eliminate the need for a second rig.

BP, who with several sets of partners is developing four huge oil and natural gas fields in ultra-deepwater areas of the Gulf of Mexico, has chosen to use a rather unique mobile offshore rig to develop one of them.

This past week, Houston-based GlobalSantaFe Corp. (GSF), the world's second-largest contract drilling company, announced that it signed a three-year contract with BP for use of the Development Driller ll (DD-ll), one of its two new-generation semisubmersible rigs, to drill and complete some 20 subsea wells planned for the Atlantis field, the third-largest ever discovered in the Gulf. The deal has a total value of about $200 million.

The $285 million rig, says GSF, currently in its final construction phase at a Singapore shipyard, is slated for delivery early next year. It is scheduled to start the Atlantis assignment on July 1, 2005, and likely will remain there for most of the three-year contract term. The DD-ll is part of a $800 million, four-rig construction program initiated in 2000 by GSF predecessor Santa Fe International. The rigs--two deepwater semisubmersibles and two high-performance jackups--were built on speculation that the offshore industry would embrace them for their added capabilities. GSF's bet apparently was a good one. Two of the rigs are now under contract.

The Atlantis field, located in the Atwater Foldbelt about 125 miles south of New Orleans in the vicinity of Green Canyon Block 743, was discovered in June 1998, and currently comprises seven blocks whose water depths range from 4,400 to 7,100 feet. Atlantis' proven and probable reserves recently were estimated at 635 million barrels of oil equivalent (boe), but the company says continued exploratory drilling in the area eventually could increase that figure. BP is operator at Atlantis with a 55 percent working interest. The U.S. subsidiary of Australian company BHP Billiton holds the rest.

When fully developed, the Atlantis field is expected to flow up to 150,000 barrels per day of crude oil and 180 million cubic feet per day of natural gas.

Atlantis is one of four significant ultra-deepwater field discoveries made by BP in the Green Canyon area since 1998. The other three are the Thunder Horse (originally named Crazy Horse), Holstein, and Mad Dog fields, all located in about the same general area and with similar water depth characteristics. The Thunder Horse field, which BP and partner ExxonMobil discovered in 1999, has estimated proven and probable reserves of at least 1 billion boe, making it the largest field ever discovered in the Gulf. Holstein and Mad Dog are somewhat smaller in size than Atlantis.

BP is a big player in the deepwater Gulf today, and one of only a handful of major companies operating in extreme deepwater. The company says it began deepwater Gulf operations in the mid-1980s (most probably through the entry back then by former competitor Amoco, which BP acquired in 2000). However, the company now produces more than 300,000 boe/d from about two dozen fields for which it either is operator or a minority interest-holder.

In the years since, development of Gulf deepwater fields (roughly, those that lie in water depths greater than 1,000 feet), while highly expensive, has become a fairly routine operation. Various operators have production flow currently underway from fields in up to 5,000 feet or so of water. And while exploratory drilling is being conducted in up to 10,000 feet of water, actual field developments in water beyond 5,000 feet deep are relatively few in number.

In most cases, operators who make such discoveries use two or more deepwater-rated semisubmersible rigs to drill and complete the subsea wells necessary to fully develop them. Typically, one of the rigs drills development wells while the other follows after it to handle the completions. Ultimately, the subsea wells are tied back to a central floating production facility, through which the hydrocarbons are sent for primary treatment prior to being routed into pipelines for export to shore. BP itself is using roughly this type of setup at many of its deepwater field developments.

But for Atlantis, the setup will differ, because the new GSF unit is both a drilling and completion rig. A two-base hit, as it were. Essentially, say GSF officials, the DD-ll eliminates the need for two separate rigs, since it is designed to arrive on location with all materials on board to both drill and complete the wells, which in the case of Atlantis, will then be tied back to a permanently moored, non-drilling equipped semisubmersible production facility. Supply vessels keep the rig's drilling and completion capacities filled as the rig consumes them.

Because the DD-ll is designed to handle continuous "batch" drilling and multiple well completions, it's big. The unit has 18,000 square feet of usable deck space--much larger than that of most other semisubmersibles, says GSF--and the capacity to handle more than 7,700 tons of variable deck load. Its interior storage capability allows for more than 50,700 tons of operating displacement. For drilling, it has a 200-foot clear derrick height, which allows handling of drill pipe in "quads" and casing in "trebles." What's more, the drilling rig itself has two independent "load paths," each with its own draw works, top drive, and traveling assembly, which will allow it to conduct both drilling and casing activities simultaneously for each well's top hole section, and to enable BOP and riser to be run while the top hole section is being completed. Additionally, says the company, the dual paths allow subsea trees to be lowered to the sea floor, ready for connection to wellheads once the drill string in the primary load path reaches total depth. These and other beefed-up well construction features will help keep drilling "flat" time to a minimum, say GSF officials.

Much of the rig's tubular goods handling, rotary drilling, and subsea well completion equipment is handled with various remote control and robotic gear to minimize risk to personnel.

The DD-ll also is equipped with redundant station-keeping abilities consisting of a self-contained, 8-point mooring system for conventional anchoring in water depths to 5,000 feet and additional line connection equipment for use with pre-set moorings in water depths to 7,500 feet and beyond. It also is equipped with a separate dynamic positioning (DP) system that can be used for both propulsion and for station-keeping assistance during tropical storms. Using all of its mooring and dynamic positioning capabilities, the rig is designed to stay on location during a severe, 100-year Gulf type of hurricane or its equivalent. That size storm, according to metocean charts, would exhibit average wave heights of 40 feet, sustained wind speeds of 95 knots/hour, and ocean current speeds of up to 3 knots/hour. The DP system also could be used alone for drilling/completion station-keeping when existing subsea architecture rules out fixed moorings.

The DD-ll's sister rig, Development Driller l, also is nearing completion at the same Singapore shipyard. The company says it's preparing bids for contracts.

According to GSF, the two Development Driller semisubmersibles were designed to operate in deepwater areas within the so-called "golden triangle," of the U.S. Gulf, West Africa, and Brazil, all of which have relatively benign weather compared to other offshore development hotspots that include the seas off Western Europe, in Arctic areas, off Australia, and in certain parts of southern and eastern Asia.