phase 4 report - DNV

RN02: DESIGN OF FLOATING STRUCTURES IN ICE // PART 4 ANNEX ACloser to the structure is the management zone, in which tracking of the features continues, the requirementfor physical management is assessed and procedures are implemented. Physical management techniques includedeflection by towing icebergs or by applying water cannon to bergy bits and growlers, pushing of large floes,breaking of thicker ice to decrease floe sizes, and breaking up of ridges or rubble fields. This list is by no meansexhaustive and all feasible means should be considered. The sizes of the zones vary according to the operationalcharacteristics of the platform and the ice environment. For icebergs off Canada’s east coast, the managementzone can correspond to drift times on the order of a day, while sea ice management zones seldom extend to drifttimes of more than a few hoursEach floating structure has one or more critical zones close in corresponding to times required to shut downproduction, disconnect risers or release some mooring lines prior to full disconnection. These circumstancestypically correspond to a series of alert levels with associated drift times estimated for the ice feature to reachthe platform. Ice management, detection, tracking and forecasting should continue as long as hazardous featuresremain within the critical zones.An ice management strategy for icebergs and many sea ice conditions is illustrated in Figure A.17-2. Detection,tracking and forecasting continue throughout the time when potentially hazardous ice features are present. Oncea threat is perceived and the feature is within prescribed time and/or distance limits (generally specified in theice management plan), ice management resources are deployed. If the threat is averted, detection, tracking andforecasting should continue until it is ensured that the feature can no longer approach the structure. Similarly,production should be suspended and the platform disconnected if the threat persists.Examples of ice management systems that have been used in ice-covered waters include––the ice management systems that have supported floating drilling operations in the Beaufort Sea [A.17-1] ;––the ice management systems that have supported a flowline installation and extended season oilproductionoperations (through a SALM buoy to an FSO) in the Okhotsk Sea off northeast SakhalinIsland [A.17-2] ;––the ice management systems that have supported drilling and production operations on the GrandBanks, and floating drilling operations in the Labrador Sea and off West Greenland [A.17-3], [A.17-4] ;––the ice management systems that have supported a range of offshore activities in the Caspian Sea,such as the protection of drilling and production structures against adverse ice events, ice clearanceto allow marine access to platforms, and icebreaking to enhance various EER approaches.Figure A.17-2 – Typical functions of an ice management system100RUSSIAN–NORWEGIAN COOPERATION PROJECT