Abstract

In order to be economically viable, Arctic floating drilling in high concentration pack ice requires very high confidence that ice interaction does not lead to costly, unanticipated emergency disconnections of the rig from the well. One of the foremost near-field ice management challenges is to maintain the station-keeping drilling rig within the managed ice channel throughout periods of complex changes in ice drift direction and speed. This entails precise, continuous re-positioning of the ice management fleet, which may be located up to several kilometers up-drift of the station-keeping drilling rig, in response to changing drift. While it may seem plausible to position up-drift ice management operations based on ice drift forecasts, forecasting unfortunately has insufficient precision to achieve the necessary level of reliability. To remedy this problem, ExxonMobil has developed systematic ice management command and control tactics that maintain the station-keeping drilling rig within the managed ice channel with high confidence. The tactics are based solely on the recent drift time history, and therefore eliminate any need for ice drift forecasting for near-field ice management operations. The tactics were proven in a series of near-field ice management tests conducted during the Oden Arctic Technology Research Cruise (OATRC 2015). OATRC2015 was performed by the Norwegian University of Science and Technology in cooperation with the Swedish Polar Research Secretariat and support and participation by ExxonMobil. Over a period of ten days during September, 2015, in which there were many complex Coriolis-driven ice drift loops and cusps and rapid drift direction changes, the methodology was able to successfully manage ice ahead of a fixed way point such that the point remained well within the managed ice channel at all times. The key features of the approach are described herein and include the use of variable length "arched racetrack" icebreaking patterns and an algorithm for continuously adjusting the position and size of the racetracks based on the measured ice drift speed and direction.

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