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SPECIAL | OFFSHORE TECHNOLOGY Drilling in ice SHIP DESIGN The challenge for discovering Arctic oil and gas reserves will be to fi nd solutions to produce gas and oil with the highest safety and environmental standards. For ice going drill vessels the Hamburg Ship Model Basin (HSVA) has done various innovative frontier developments. Karl-Heinz Rupp, Walter L. Kuehnlein It is estimated that the Arctic contains more than one third of the world’s undiscovered oil and gas reserves. Although some developments have already occurred, the region remains one of the last energy frontiers. But the region is also one of the most diffi cult areas in the world to work at, due to its remoteness, the extreme cold, dangerous sea ice and its fragile environment. Big energy companies are preparing to go into the Arctic, they are taking measures in order to ensure that they will operate safely and responsibly. This is not the fi rst run to the Arctic. Petroleum companies entered into the Arctic already half a century ago. Experiences from past Arctic developments show the potential hazards of further exploration. A key challenge will be developing and deploying solutions, which are currently at the cutting edge of technology. The Arctic Ocean is the only major sub-basin of the world’s oceans that has only occasionally been sampled by deep sea drilling. Today the properties of the Arctic Ocean are being focussed upon by both researchers and commercial oil and gas drilling companies. Research core drilling is of great importance for the researchers because it allows them to increase their knowledge about that large ice covered area. And of course the present high prices for energy make it profi table to explore for reserves and to produce energy even in the ice covered waters of the High North. Drilling operations in ice have been already carried out at the ice border with “open water drill ships“, mainly with the support of icebreakers (e.g. “Joides Resolution” with “Maersk Master”). Some drill ships are reinforced for operation in ice, but this reinforcement is limited to the strengthening of the ship structure and does not include the propulsion and operational outfi tting. An ice-breaking drill ship should be capable of keeping its position so that the drilling operation can be continued, also when it is surrounded by drifting ice. Existing concepts and d esigns Some of the challenges which a drill ship in ice will experience, have been already described in 1983 (Dynamic Response of a Moored Drill ship to an Advancing Ice Cover, T. Kotras, A. Baird, E. Corona, Poac 83, Volume 3, Fig.1.: The cross section shows the sloped side of the HSVA drill ship design with ice accumulated Special 8 Schiff & Hafen | June 2008 | No. 6 page 433, Helsinki, Finland, 1983): � “The ability of a vessel to stay within a prescribed operational radius is greatly enhanced when impacting ice in a head-on condition. Beam-on collisions cause excursions from two to fi ve times larger as those occurring head-on. � The ability of a drill ship to quickly yaw into a heading inline with the advancing ice is directly related to the maximum excursion seen. � In the Bering Sea, an unassisted drill ship may not be capable of year round operation during the heavy ice periods, ...“. Almost 30 years ago, in 1980, a drill-platform from Gulf Canada (Conical Drilling Unit) was tested in ice by HSVA. It was found that the rig could operate in an environment up to about one meter level ice thickness. This platform, the “Kulluk“, was kept in position with a mooring system. The shape of the platform was circular in the plan view and the section was similar to an asymmetrical sandglass. The turret was placed in the centre of this fl oating island. This platform was not suitable for being moved over a long distance at sea. In the last decade improvements in manoeuvrability and Fig.2: Side view of “Aurora Borealis“ with two moonpools (as designed by HSVA) ice breaking performance have been achieved by applying azimuth propulsors. Nowadays several ice going and ice breaking vessels, e.g. icebreakers, supply vessels, tankers and multi-purpose container vessels are equipped with this type of propulsion system. New technical developments In 2000 contracted the Alfred- Wegener-Institut (AWI) in Bremerhaven Germany (www. awi-bremerhaven.de) the Hamburgische-SchiffbauVersuchsanstalt (HSVA) to carry out a draft design study for an Arctic Drilling Research Vessel with dynamic positioning capabilities in ice. The project was entitled “Aurora Borealis”. Drifting ice may change in both in speed and direction. Furthermore the ice conditions vary from easy to heavy (e.g. ice ridges), therefore the drill ship must be able to keep position within a very narrow margin. All of these requirements, as well as the technological developments described above have been taken into consideration for HSVA’s conceptual design for the “Aurora Borealis”. The technical features of the HSVA design are:
� Low ice resistance of the drill ship at both bow and stern. This was achieved with an optimized icebreaking hull shape, similar to that of an icebreaker. � High ability to turn the vessel in ice in order to follow changes in ice drift. This was achieved by implementing a strong slope at the side of the vessel (see cross sections). This hull shape allows the vessel to break ice over the entire ship length. In order to break the ice the azimuth propulsors deliver the required thrust for turning the drill ship. � The vessel is able to operate in ice without icebreaker assistance up to very severe ice conditions, far above of the capabilities of all existing ice going drill vessels. With icebreaker assistance the operational limits of the drilling vessel can be further extended. � Consequently, the HSVA design is the fi rst design world wide, which will allow drilling in ice with a dynamic positioning, i.e. no fi xed mooring system will be required. The HSVA design study for “Aurora Borealis” has been presented in several publications and presentations since 2001. The fi gures 1 and 2 are from: European Polar Board (EPB), Aurora Borealis “A long term European Science Perspective for Deep Arctic Ocean Research 2006-2016”, June 2004. Logistics in ice management In addition to the technological improvements, the logistics in ice management are also of great importance. The use of modern satellite ice and weather data are a fi rst step for obtaining information about the ice conditions ,ice drift speed and drifting direction over a large area. Closer to the drill ship, ice drift speed and direction can be detected by sensors installed on board of the drill vessel. The ice thickness can be measured with electro magnetic ice thickness measurement devices and together with visual ice observations, severe ice conditions can be detected and traced, and the potential danger to the drill ship can be calculated and predicted. An example for excellent ice management was the core drilling research work of “Vidar Viking” in 2004 close to the North Pole. “Vidar Viking” was built as an ice breaking supply vessel and was equipped with a drilling rig. The vessel alone was not able to keep position during drilling in the Arctic ice, although it is equipped with a dynamic positioning system (DP) for ice free waters. Manual DP in ice was only possible in well managed ice. The Russian nuclear icebreaker “Sowjetski Sojus“ and the Swedish Icebreaker “Oden“ broke the drifting ice into small pieces (well managed ice). Tests with a moored drilling vessel in drifting ice HSVA has tested several drilling, production and storage vessels in managed and in well managed ice. In these tests the ice drift is supposed to hit the vessel under different angles. Such “oblique towing tests” generate large deviations to the vessel’s position and the corresponding loads in the mooring systems. During the last few years HSVA has designed and/or optimized several of these vessels and consequently HSVA has gained a tremendous amount of expertise for such highly complex systems in ice. As an example: From 2006 until 2008, HSVA carried out several ice model testing campaigns for a moored drilling vessel for the Norwegian engineering company LMG Marin in Bergen and Statoil (now StatoilHydro). The tests demonstrated the excellent ice breaking capabilities of the unit in level ice of up to 1.60m thickness, in ice ridges and in ice rubble fi elds. The main target of the investigations was to develop a concept for enabling the vessel to follow the ice drift change in order to keep the vessel within the range of the lowest ice resistance and therefore within the defi ned operational working area. The pictures 3–6 give an overview of several ice scenarios which have been tested. Dr. Karl-Heinz Rupp, Dr. Walter L. Kuehnlein Hamburg Ship Model Basin (HSVA), Hamburg Rupp@hsva.de Kuehnlein@hsva.de www.HSVA.de Fig. 3: The vessel is rotated around the centre of the turret using the thrust of the azimuth propulsors Fig. 4: The propeller wash is a useful tool for breaking ice or to wash ice away from the vessel Fig. 5: Track behind the drill ship after an ice drift course change of 20° Fig. 6: Tests in broken irregular thick ice Schiff & Hafen | June 2008 | No. 6 9 Special
Page 1 and 2: � � � Underwater Vehicles: Ma
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Page 11 and 12: Side view of a new Offshore Supply
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Page 17 and 18: Fig. 3: Drilling unit with barge ty
Page 19 and 20: Hydrocarbon sensor systems PIPELINE

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