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Atlantis: Mastering the deep

Release date: 03 January 2006
Atlantis platform
Drilling is scheduled to begin later this year on the BP-operated Atlantis deepwater project in the U.S. Gulf of Mexico (GoM). The deepest moored production facility in the world, Atlantis is an important part of the company's estimated $15 billion investment this decade for the exploration, development and production of BP's significant leaseholdings in the Gulf.
Atlantis boasts several attributes that set it apart from its better-known development program predecessors — Holstein, Mad Dog and Thunder Horse. In this case, finishing last proved to be a benefit as the team greatly enhanced their performance by applying lessons learned from the other projects.
Atlantis is scheduled to be moored in the fourth quarter of this year in the Gulf about 298 km (185 miles) south of New Orleans, Louisiana, in Green Canyon block 787 in a record water depth of 2,156 meters (7,074 feet). Atlantis weighs about 46,856 tonnes and displaces 88,826 tonnes, making it the second largest semi-submersible in the world, smaller only than Thunder Horse.
The Atlantis mooring system includes the longest continuous wire mooring ropes ever built. Twelve large steel canisters, called suction piles, are embedded in the ocean floor to anchor the platform in place. Part of the chain used in this mooring system is the largest of its type in the world.
BP, which is also the pre-production operator of Atlantis, holds a 56% working interest and partner BHP Billiton owns the remaining 44% interest.

Wells aplenty

The Atlantis development plan calls for drilling and completion of 16 production and 4 injection wells in the adjacent Green Canyon block 743. The host facility is designed to process 200,000 barrels of oil and 180 million cubic feet of natural gas daily. The oil and gas will be exported to shore via the BP-operated Mardi Gras transportation system. The Atlantis team chose to partner with a rig contractor and have their drilling and completion group participate in the design and construction of a new-build rig. The design of BP-operated Na Kika, which was built by the pre-production operator Shell, follows the same logic.
"The decision to have a rig or not is influenced by many factors," says Gary Imm, Atlantis project deputy manager. "Rather than simply take delivery of a rig, we had a rig built to provide us more extensive, flexible capabilities."
The result was a long-term contract with GlobalSantaFe, which tailored the design of their semi-submersible drilling rig Development Driller II (DD2) to the Atlantis project. Unlike most drilling rigs that focus exclusively on drilling, completions and installation of well trees, the Atlantis team helped to design DD2 to also function as a construction vessel to put in place major elements of subsea piping that rest on the bottom. "We will use the DD2 to install piping and heavy equipment that interconnects the wells to fully exploit the construction capabilities of the vessel," adds Imm. One of the advantages of Atlantis' design is the generous deck space and payload capacity on the host facility created by the absence of a drilling rig.

Seismic technology

When Atlantis was sanctioned, its design was based on the best understanding of the reservoir that existed at the time. Much of the hydrocarbons in the field are beneath salt formations and more difficult to image, but rapid advances in technology since sanctioning in November 2002 have led to increased confidence in the reservoir's potential.
Although Imm states that Atlantis was reluctant to use unproven technology, cutting-edge innovations were incorporated when they made sense. One example is an array of seismic sensors that sits on the bottom of the ocean, which mitigates many of the problems encountered when towing a seismic array on the surface. This remote network of sensors — well over 1km (0.5 mile) deep in the case of Atlantis, provides improved definition of the reservoir, which Imm believes will help sustain maximum production levels.
Imm adds that the Atlantis team also took the initiative to preserve any spare capacity in the hull and production quarters topsides. They worked diligently to keep the topsides modules and hull close to their design weights. This, coupled with the lack of a drilling rig, made it possible for the team to design the host facility to accommodate twice the number of risers required for the number of wells currently planned.
"Atlantis is prepared for future production growth," he adds. He also notes that Atlantis logged more than four million man-hours during hull construction without a single recordable incident.
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