Abstract

As the industry moves further offshore in the Arctic where open water seasons are small to non-existent, ice management will be a critical enabling technology to allow floating vessels to keep station (for drilling, tanker loading, well workovers or subsea equipment maintenance). This paper describes some of the key considerations for accomplishing the complex task of ice management and demonstrates a simulation-based means for testing the efficacy of various tactics against measured ice data. Examples are provided wherein published ice management fleet deployment scenarios are evaluated using measured ice drift and thickness time histories provided by the Canadian Department of Fisheries and Oceans for prospective drilling sites in the Canadian Beaufort. The results provide insight into the ice management fleet composition, fleet deployment strategies and frequency/duration of expected downtime due to ice conditions that would exceed the operating limits of the fleet.

Introduction

A major challenge of high-Arctic development lies in water depths exceeding about 100 m, where the traditional bottom-founded structures become impractical and stationary floating vessels are required for drilling and other key offshore operations. Unmanaged drifting sea ice can generate loads far beyond the capabilities of conventional station-keeping systems that use either dynamic positioning (DP) or anchored moorings. Ice management -- the process of protecting a stationary vessel in moving ice using icebreakers working upstream of the vessel to create a continuous channel of thoroughly broken-up floes (Figure 1) -- is required to reduce ice loads to manageable levels. Contrary to traditional icebreaker operations, where escort icebreakers exploit weak zones in the ice to create a channel for a transiting vessel, ice management for a stationary vessel must deal with whatever ice drifts across the fixed location. Amongst the challenges is that sea ice frequently drifts at speeds over 1 knot, which can make it difficult for a reasonable number of icebreakers to process the ice into sufficiently small floe sizes. Additionally, the ice drift heading varies constantly, with frequent changes of 180 degrees or more in a few hours, which challenges the fleet's ability to maintain the protected vessel within the managed ice channel created by icebreakers working updrift in the moving ice. Finally, some multi-year ice floes in the high-Arctic are too thick to be broken by even the largest conceivable icebreakers, so it is important to know the frequency with which these features may be encountered.

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