JBF Arctic - a Mobile Offshore Drilling Unit with High Performance in Ice Covered Waters and in Open Seas

Abstract

Abstract Due to the increasing demand in oil and gas worldwide, the rise of the National Oil Companies and the end of easy oil, International Oil Companies are forced to look for oil in the more challenging and harsher environments in the world like the Arctic regions. These regions are known for their extremely low temperatures and high winds, but even more challenging in offshore operations are the combination of the high waves in the open water season and the thick ice in the cold seasons. This paper presents the development of a new versatile column stabilized Mobile Offshore Drilling Unit; " The JBF Arctic??, that is optimized to work in these extreme seasonal conditions. The exceptional seakeeping characteristics in open water are achieved at the traditional operating draft. At the deeper ice draft, the unit has an excellent ice resistance. The unique mooring system will be capable of holding the unit in position in ice draft under the ice loads of 1.5-2.0m of unbroken drifting ice. The paper presents the results of significant research on the optimization of JBF Arctic design, the results of the seakeeping calculations, model testing in a seakeeping tank, studies of the ice loads, model testing in an ice tank, and the analysis of the mooring system design. Major conclusions are drawn and the feasibility of the design is evaluated. Also, special consideration is given to the drilling and handling equipment in order to make it suitable for the low temperature Arctic conditions. The new JBF Arctic design allows drilling operations during the whole year in the harsh Arctic environment using one draft optimized for open water conditions and a deeper draft for ice covered waters. Introduction Traditionally semi-submersible drilling units or drill ships are utilized for offshore exploration drilling in open waters. Monohull drill ships have acceptable seakeeping characteristics for mild and intermediate environmental conditions. When the environment gets harsher, semi submersibles are deployed because they have a better seakeeping performance compared to the monohull type vessels. In Arctic conditions in ice covered waters gravity based structures can provide excellent ice resistance. However the application of this type of drilling installations is limited to shallow water areas. When the ice infested waters get deeper ice reinforced drill ships can be utilized. Even though, these vessels are properly reinforced for operating, or actually for transiting, in ice, their station keeping capability is very limited. When a vessel cannot choose heading to meet the ice with its bow DP or a mooring system can only withstand very light ice loads. Drilling units specially dedicated for Arctic waters often have a cylindrical body with a conical shaped structure at the level of the ice water line for breaking ice. These can be relatively tall spar type units or shorter cylindrical structures [1, 2]. A well-known existing drilling unit specifically designed for ice conditions is Kulluk [3, 4]. All these designs have good ice resistance and sophisticated mooring systems. However, the seakeeping performance of the relatively short cylindrical units is quite poor since the natural heave period is well within the typical wave periods range. The spar type units have good seakeeping characteristics but the ability to move between the drilling locations is very limited and the application of these units requires large water depths.