One of the latest pieces of subsea hardware to come out of Norway is Atlantis, a prototype drilling and intervention buoy that allows equipment not rated for deepwater to be used at greater depth.

Atlantis effectively "moves" the seabed nearer the surface, allowing less costly drilling and intervention on deep fields.

Both BP and Shell have provided research and development funding for the concept, which is an artificially buoyant seabed (ABS) providing a working platform submerged between 656 ft and 984 ft (200 m to 300 m) subsurface. Deeper drilling or intervention operations can be launched without the requirement to qualify all equipment to the ultimate operational depth.

Instead, the technology permits a first casing string to tieback to a rig, while casing and connectors from a deepwater wellhead bring the production flow nearer to the surface. It avoids handling a longer riser and a heavy deepwater blowout preventer stack.

Using this technology could offer savings between 20% and 40% on deepwater drilling time and cost, depending on the depth and complexity of the well being drilled.

With an Atlantis ABS in place, drilling operations are the same as for a shallow depth well - the only deepwater requirement is for station-keeping.

"Most of the cost savings come from the fact that you can use second or third generation lower rated shallow/mid-water drilling rigs in deepwater, combined with taut-leg mooring systems, which can halve the dayrates of deepwater rigs," said Paal Norheim, managing director of Atlantis Deepwater Technology Holdings (ADTH) which now owns the technology.

Development of the technology dates back to the mid 1980s when inventor Terje Magnussen, then working for Statoil, first considered the concept to overcome costs for deepwater drilling. But it received a substantial shot in the arm when it was included in October 2001 in Norway's Demo 2000 project managed by the Norway government's Oil and Energy department, to qualify technology for greater depth. Shell and BP, along with ADTH, financed the design, construction and testing of a full-scale Atlantis prototype, costing US $5.6 million. Constructed at the Nymo fabrication yard in Norway, the prototype was transported to Gandsfjord, near Stavanger, Norway, for sea testing. This involved the use of two anchor handling vessels, two remotely operated vehicle (ROV) spreads, plus a utility vessel, indicating the deployment required for installation of the device.

During sea-testing carried out in April this year, the 350 tonnes prototype, measuring 52.5 ft (16 m) in diameter and 23.6 ft (7.2 m) high confirmed towing ability at speeds up to 5 knots and its sea-stability with variations in trim. After this test, ADTH had confirmed the towing characteristics and said they were in line with previous calculations.

Compressed air pumping and venting was carried out to verify actuation of valves fitted to the prototype both on the surface and while the unit was submerged while attached to an umbilical line. This was done after the unit was taken to its proposed operational depth of 656 ft (200 m) within an hour, using chain weights, to establish the operation of the buoy, and the effects of currents on the structure.

While submerged, further testing verified the operation of the ballast water system by ROV. The test unit was also successfully brought back to surface at the conclusion of the exercise.

Deployment of the concept is now being sought by testing in a live drilling environment:

"We have now done what we consider required inshore, before we go offshore for a real application, involving use of a drilling vessel," Norheim said. "We are now prepared to go for a real exploration drilling application."

He would prefer a benign environment, such as India, where more than 50 deepwater wells are planned within the next few years, or offshore West Africa, including on BP's Block 18 discoveries off Angola.
Although licence partners in Block 18 have helped finance research and development to date, the likelihood is that Atlantis may see first deployment elsewhere. "The use of the technology in the area is still being discussed with BP and others," reported Norheim. "We are, however, in discussions with ONGC [India's Oil and Natural Gas Corporation] about using the technology."

He said discussions have also been held with contacts for using the concept in deepwater offshore Nigeria, using local fabricators to construct Atlantis.

"With respect to current development work we are now focusing on the Atlantis 3-well producer version and we are also developing the Atlantis riser tower for a deepwater oil company," Norheim added.
Meanwhile, ADTH has formed global joint ventures to provide the required local content for application of the technology in Brazil, India, and Nigeria, and another is being formed for Angola.