Ice Loading of Jack-Up Platforms

The use of drilling platforms for exploration drillings in ice-covered shallow water is expected to increase in the future. Jack-up platforms (JU) are regarded to be most suitable for exploration drillings due to their high mobility, their facile transportation and installation. Although having proved their capability for harsh environments, e.g. in the North Sea, jack-ups have neither been especially designed for nor have been operated frequently in icy waters. The problems associated with the operation of jack-ups in ice waters are related to structural integrity as well as to operational limitations. One objective of the research project MATRA-OSE was to check the design of JU for exploration and oil production in ice-covered, shallow-water areas. The global stability of JU as well as local and global loads acting on a three-legged jack-up drilling unit were investigated. The design loads were determined by analytical approaches. Different ice load cases were defined as the basis for the detail design. These load cases include local loads on single members of the platform legs like chords or braces as well as global loads, which may act on one individual leg or on several legs of the platform. Vertical forces, which result from a change of the water level (up-surge and down-surge) in case ice sheets are frozen to the platform legs were considered. Also the impact of ice being jammed between the platform legs was investigated. It has been found out that the most critical load case results from the ice being jammed between the platform legs. It should therefore be tried in practice to avoid the ice jamming by proper ice management, as the large ice loads calculated for this scenario may result in problems for the stability of a JU. Ice breakers could be used to pre break the ice and should try to clear the site from broken ice pieces before it starts to accumulate.Copyright © 2005 by ASME