The challenge of ice incursion remains a major obstacle to prolonged drilling operations in Arctic waters, posing a technical risk for traditional rigs and restricting them to work in the short ice-free season. Steve Marshall talks to Sevan Marine about its proposed cylindrical solution.
Development of new rig concepts with the ice-breaking capability needed to extend the operational window is seen as a critical enabler to unlock potentially vast untapped hydrocarbon resources trapped hundreds of metres beneath the Arctic seafloor.
The potential value of these resources has been undermined by falling oil prices, however, discouraging explorers from prospecting in a high-cost frontier region fraught with environmental risk and leaving new rig development projects in the freezer.
However, Sevan Marine has not given up on its innovative cylindrical Arctic rig concept and is now seeking a progressive-minded client willing to break the ice and make it a commercial reality. The Norwegian floating technology developer remains, unsurprisingly, convinced of the concept’s commercial and technical merits, given the circular hull’s proven capability in harsh environments.
Sevan developed a version of its cylindrical hull with ice-breaking capability that was verified by scale-model testing in an ice test facility. The tests were carried out as part of a study for Statoil related to the Shtokman gas project off Russia, which has since been shelved.
Extreme conditions of annual and multi-year ice up to two metres thick, ice ridges with a depth of up to two metres and sheet ice with a drift speed of up to two metres per second were modelled during the tests. In order to withstand such severe sea ice, the hull shape was modified to make it slope outward, thereby giving the rig better ice-breaking capability than one with a perpendicular side.
Last year, Sevan, in collaboration with Seadrill-owned Sevan Drilling and North Atlantic Drilling, developed a drilling unit suitable for the Arctic, following a study commissioned by ExxonMobil.
The trademark cylindrical design is already in use for drilling, floating production and accommodation units operating in the North Sea, Gulf of Mexico and Brazil.
Sevan has also applied its experience in developing the Sevan 1000 FPSO for Eni’s Goliat oilfield in the sub-Arctic Barents Sea off Norway, where operation in a cold climate required significant new developments.
For drilling applications in Arctic environments, the design offers the possibility of seasonal extension, limited only by the availability of supply services. The rig would be able to work self-sufficiently in the Arctic for at least 60 days and is intended for permanent mooring in order to resist ice loads.
Topsides, including pipework and cabling, would be fully enclosed on the winterised unit, which would also have a rapidly disconnectable mooring system so the rig could make a quick getaway in areas exposed to icebergs or extreme ice conditions.
The cylindrical design also eliminates the need for “ice-vaning” compared with ship-shaped units, which are more exposed to variable drift. Ice loads hitting different parts of the vessel pose a greater risk to position-keeping for ship-shaped vessels.
Sevan’s business development chief Fredrik Major claims the concept has a significant cost advantage over a drillship, as it does not have a costly and complicated turret that would be required on a ship-shaped unit for vaning in ice.
He pointed out that a drillship would be required to have mooring lines housed together with drilling equipment within the turret, which would make for “a very complex and congested area”.
The Sevan rig, on the other hand, would have enclosed mooring lines and carry out drilling through a protected moonpool.
“The circular shape makes it better able to withstand pressure from ice with varying drift direction than drillships, while avoiding the risk of encroachment from drifting ice with an open-hulled semi-submersible unit,” Major says.
The company is also touting the inherent advantages of the circular concept in terms of high deckload capacity and improved stability in harsh environments.
The winterisation issue is, of course, a major challenge in developing such units capable of operating in extreme temperatures as low as -500 Celsius. Again, the experience gained from the Goliat unit, which has a fully enclosed topsides and a heating system to de-ice critical equipment and areas, has proven instructive for development of the Arctic rig. Furthermore, ventilation panels have been developed to maintain an enclosure that keeps out snow and wind while facilitating natural ventilation in the event of gas leaks.
Sevan has already gained approval in principle for the so-called ICE concept from Norwegian classification society DNV GL. Major says the company is now also looking at a potential hybrid floating production unit with drilling capability for Arctic waters.He contends the cylindrical drilling unit “is a simple and robust design that would be easy to construct”, given it is based on proven technology, and he is hopeful of seeing a newbuild Arctic rig hitting the ice within five to 10 years.
However, getting the Arctic rig concept from the drawing board to the shipyard remains a conundrum in the current investment climate, with no one yet willing to take the risk of adopting the concept for a concrete project.Major admits low oil prices, coupled with earlier rig incidents for Shell off Alaska and sanctions on Russia, have acted as a dampener on industry interest for investments in new Arctic rig technology.
Even so, he insists it is a potential game-changer as it would facilitate a “significant extension” of the drilling season in the Arctic, thereby cutting rig costs due to prolonged utilisation and less need for mobilisation.Sevan chief executive Carl Lieungh contends the concept could still offer economic benefits for cost-conscious oil companies willing to think counter-cyclically in the current climate, both in terms of reduced newbuild prices and the estimated 15% to 25% lower cost of the cylindrical design compared with traditional drillships.He says: “All the engineering is basically done and the Arctic rig concept is close to completion, so it is really only a matter of finding the right prospect and the right client.”
The company has received inquiries from players looking at possible application of the technology in areas where previously traditional solutions have been used, he says.“The present focus on cost-cutting amid low oil prices is positive for the industry. We believe that, for certain areas, applications and projects, we may have a good solution also from that perspective,” Lieungh says.
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