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In March 2017, Statoil performed station-keeping trials in drifting ice in the Bay of Bothnia with two anchor handling tug supply vessels, Magne Viking and Tor Viking. The primary objective of the Station-keeping Trials in Ice project (SKT) was to gather full-scale data on a stationary floating structure in ice. The data will be used for validation of numerical and physical models, that will in turn increase confidence in modelling tools for design and operation in ice-covered waters. The principal requirement of the project was to safely collect the maximum amount of data meeting the quality requirements within the available budget and timeframe. This paper presents the overall project planning and execution, while more details are provided in the companion papers.

In March 2017, Statoil performed station-keeping trials in drifting ice in the Bay of Bothnia. The anchor handling tug supply vessel Magne Viking, performed station keeping operations in various ice conditions, including managed and non-managed ice. Physical ice management was used to manage the approaching ice to a target condition suitable for the station keeping tests, and to enable other essential operations including deployment and retrieval of the mooring spread and other equipment. Given the objective of the trials, physical ice management activities were performed in such a way to allow investigation of various relevant parameters that influence the managed ice condition. Additional tests were also performed for the sole purpose to assist with validation of Aker Arctic’s ice management software “AIMS”, including tests designed to estimate the performance of the vessels under different ice conditions. This paper focuses on the physical ice management operations performed by the ice management vessel Tor Viking (TV) during the Station Keeping Trials in ice (SKT). Also included is a discussion on how AIMS was used in the planning phase and how simulations compared with actual observations.

The objective of this paper is to demonstrate how modelling can be used to account for the inherent correlations while assessing the pipe response to ice gouging – and thus narrow down the uncertainties associated with the pipeline design process. A custom-developed numerical model of ice gouging has been developed and exercised to better understand how the environmental conditions affect the gouging process. Further, numerical simulations of the keel-soil-pipe interaction have been performed, relating to the input and output of the ice gouging model. The ice gouging simulations quantitatively demonstrated the effect of the governing parameters on the gouge depth. Geotechnical conditions are very important as the main source of resistance against the driving force from ice, making a noticeable difference in the gouge depth. Force balance is also important, in particular how the vertical forces are generated or/and limited by natural phenomena such as the shape of an ice feature, seabed topography and tides. The effect of the driving force and the keel resistance limits have not been dealt with within the scope of the present study. The ice gouging simulations demonstrated that ridges with steeper rake angles result in deeper gouges. Similar gouge depths have been attained irrespective of the path – via water level changes or via seabed slope - as long as the driving force was available. The keel-soil-pipe simulations demonstrated that increasing the rake angle results in lower pipe response. Deeper gouges give larger effect at the same clearance between the top of the pipe and the gouge bottom. Considering the performed simulations jointly, it can be concluded that selecting the n-year gouge depth implicitly sets the conditions for assessing the variability in the additional governing parameters. This is mainly applicable to the keel's rake angle as the factor having the strongest correlation with the gouge depth, keeping other parameters unchanged. Appreciating the correlation above and its effect on the n-year pipeline load effect can prevent possibly overly-conservative parameter combinations. It is argued that steeper keels have the highest potential to produce deepest (extreme) gouges. For these conditions, the extreme gouge load effect seems to be acceptable as long as there is a gap between the pipe and the ice keel and the pipe wall thickness is relatively large. Thus, the pipeline design against ice gouging load effects is likely to be governed by the maximum gouge depth, as the gap itself is found to define a sharp limit between an acceptable and an unacceptable design condition. In turn, this sets high requirements to reliable determination of the gouge depth.

The Shtokman gas condensate field lies in the centre of the shelf zone of the Russian sector of the Barents Sea about 600 kilometers northeast from Murmansk. Shtokman Development AG (SDAG, 51% Gazprom, 25% Total and 24% Statoil) is in charge of the integrated development of the phase 1 of the Shtokman Gas condensate field. Exploitation of the gas field will be done through a floating platform that will export gas and condensate to the shore via pipeline. Significant sea ice invasions occur at Shtokman in approximately 3 out of 10 years, on average. Icebergs may also occur in the SCGF area. Ice and iceberg management activities have been planned to support the operations. The ice and iceberg management activities include surveillance, threat assessment and physical management. At this stage, definitions of strategy and philosophies for ice and iceberg management have been developed and preliminary plans for the main tasks have been outlined. The present paper describes the different components of the ice and iceberg management system and the rationales for the main technical choices. 1 INTRODUCTION The Barents Sea is bordered by the cold and icy waters of the Arctic Ocean and the Kara Sea on the North and East sides and by the warm water of the Norwegian Sea on the west side. The Gulf Stream enters the Barents Sea as the North Cape and Spitsbergen branches of the Norwegian current, bringing warm water into the region. The border between warm and cold water varies in location, depending on the oceanographic and meteorological conditions; this change is more sensitive in the Eastern part of the Barents Sea and especially at the Shtokman field. Sea ice does not form at Shtokman (except very thin ice in very cold years) but is exported from the North - Northeast by persistent winds. Thus, the origin of ice which can arrive at Shtokman is North-Eastern Barents Sea and possibly Kara Sea. The presence of drifting sea ice is observed in approximately 40% of the years on the Shtokman field, based on satellite observations from 1974 to 2007. This means that sea ice in the Shtokman area occurs approximately once every 2.6 years. Sea ice arrives rapidly at the Shtokman area and ice concentration may increase from 2/10th to above 8/10th within a few hours. Furthermore, ice may not be continually present at Shtokman throughout any one ice season. Historically, icebergs have been observed near Shtokman (within 75 nm) about once every five years on average. 10% of icebergs observed within 25 nm circle around Shtokman were in ice while 40% of icebergs observed within up to 100 nm north of Shtokman were in ice. With regard to seasonal variation it must be assumed that the probability of encountering icebergs at Shtokman during spring is higher than during late summer / early autumn.