Jackup Designed for Optimum Operational Time in Ice Conditions

2012 ◽  
Author(s):  
Ove T. Gudmestad
Keyword(s):  
Ice Cover ◽  
The Arctic ◽  
Shallow Waters ◽  
Current Load ◽  
Fall Season ◽  
Arctic Conditions ◽  
Ice Conditions ◽  
Drifting Ice ◽  
Ice Pressure ◽  
Operational Time

There is at present a large interest in exploration for hydrocarbons in the Arctic. In shallow waters, up to, say, 70m, jackups are utilized outside the ice season, while there is a wish to extend the season when the jackups can be on site. We will report on an attempt to extend the operational season to earlier installation and later decommissioning than possible with present jackup designs for ice conditions. The installation of the jackup can take place after the ice cover has cleared sufficiently for the jackup to be maneuvered to site. It should be noted that remaining drifting ice ridges may represent a hazard as the drift of these into the jackup legs can damage the legs. The situation is particularly vulnerable when waves or strong currents cause the remaining of the ridges to impact with the jackup legs. During the operational season the jackup will operate in conventional mode. This phase should NOT been forgotten in the design as the wave and current load on the jackup might be higher than the ice pressure. Towards the end of the drilling season and prior to ice aggregation, the operator of a conventional jackup rig will become very cautious of the requirement to move the jackup out of the ice cover in due time before the sea freezes up and the jackup could get stuck in the ice cover. It should be noted that a jackup frozen into the ice cover and susceptible to loads from drifting ice sheet and ice ridges might collapse. Should the situation occur that the jackup be frozen into the ice cover, it would be necessary to call for costly ice breaker assistance to free the jackup. A jackup that could stay in the ice for a longer period in the fall season would extend the drilling season considerably. In the case such design be considered, the strength of the foundation should be checked to avoid loads that will exceed the foundation capacity of the mud mats. We will in this paper in particular discuss how we can deal with the problem of the requirement for an extended drilling season. The paper covers some of the main issues that are governing for the design of a jackup for arctic conditions. We will in particular cover the issue of leaving the offshore location safely as late as possible when ice has started to form. In this situation traditional jackups have problems and could need the very costly assistance of icebreakers. Other important issues that are not covered are the behavior of the jacket in ice. It should, however, be noted that the jackup is designed to leave the location prior to the ice situation becoming unmanageable.

Temporary seismic network on drifting ice in the North Barents Sea

2020 ◽  
Author(s):  
Andrey Jakovlev ◽  
Sergey Kovalev ◽  
Egor Shimanchuk ◽  
Evgeniy Shimanchuk ◽  
Aleksey Nubom
Keyword(s):  
New Technologies ◽  
Barents Sea ◽  
Seismic Signal ◽  
Ice Cover ◽  
The Arctic ◽  
Stick Slip ◽  
Seismic Stations ◽  
The North ◽  
Drifting Ice ◽  
Ice Floes

<p>Despite the strong attention to the investigations in the Arctic its advance quite slowly. The harsh climatic conditions and big expenses slow down realization of the fieldwork in high latitudes. Therefore, scientists from over the world looks for new technologies, which could optimize and reduce the costs of the fieldworks that aimed at investigation of the geological structure beneath the Arctic Ocean. From March to May 2019 scientific expedition on the Expedition Vessel “Akademic Tryoshnikov” operated by the Arctic and Antarctic Research Institute that belongs to Rosgidromet were conducted in the framework of the program “TransArctica 2019” first stage. In the framework of the seismological experiments 6 temporary seismic stations at 4 different locations were installed on a drifted ice floe in the North Barents Sea. The first aim of the experiment was to elaborate technology of installation of the seismic stations on the drifting ice floes. The second aim was to check if obtained seismological records could be used for registration of the local and remote earthquakes, which are meant to investigate the lithosphere structure in the Arctic regions, and for investigation of the processes within the ice floe.</p><p>The stations were installed in the April 2019 on the ice floe near the EV “Akademik Tryoshnikov” that were “frizzed” in the ice floe and drifted together with them. After analysis of the recoded data the following types of the seismic signal generated by processes in the ice were observed:</p><ul><li>- background signal from bending-gravitational waves with periods from 1 to 30 sec. Swell waves with periods from 17 to 30 sec were observed permanently during the whole period of network operation;</li> <li>- continuous mechanical vibrations (self-oscillations) with a period of up to 2-3 sec;</li> <li>- stick-slip relaxation self-oscillations with a period from 0.1 s to several minutes;</li> <li>- mechanical movements of ice due to compression or stretching of ice caused by chaotic different scales fluctuations in the drift velocity of ice floes;</li> <li>- process of ice fracturing due to compression or stretching of ice.</li> </ul><p>Results of monitoring of the ice cover has shown that in the most cases there are no direct correlations of processes within the ice floes and local hydrometeorological condition. During the process of ice cover fracturing an increased value of the ice horizontal movement were observed. Analysis of the seismic signal from ice events has shown that stick-slip events preceded origin of the ice fractures.</p><p>As a result of the initial analysis of the seismograms several signals from remote and regional earthquakes were detected. For example, an earthquake that according to the ISC bulletin occur at 08:18:23UTC on April 11, 2019 near the Japan (40.35°N, 143.35°E, 35 km depth, MS = 6.0) were detected. A local earthquake that occur approximately at 05:58UTC on April 10, 2019 at a distance of ~500 km. Due to close location of stations to each other the localization of the earthquake is impossible.</p><p>This work is supported by the RSCF project #18-17-00095.</p>

Landfast ice zoning from SAR imagery

2020 ◽  
Author(s):  
Valeria Selyuzhenok ◽  
Denis Demchev ◽  
Thomas Krumpen
Keyword(s):  
Time Series ◽  
Sea Ice ◽  
Ice Cover ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ice Drift ◽  
Landfast Ice ◽  
Sea Ice Drift ◽  
Ice Conditions ◽  
Sar Imagery

<p>Landfast sea ice is a dominant sea ice feature of the Arctic coastal region. As a part of Arctic sea ice cover, landfast ice is an important part of coastal ecosystem, it provides functions as a climate regulator and platform for human activity. Recent changes in sea ice conditions in the Arctic have also affected landfast ice regime. At the same time, industrial interest in the Arctic shelf seas continue to increase. Knowledge on local landfast ice conditions are required to ensure safety of on ice operations and accurate forecasting.  In order to obtain a comprehensive information on landfast ice state we use a time series of wide swath SAR imagery.  An automatic sea ice tracking algorithm was applied to the sequential SAR images during the development stage of landfast ice cover. The analysis of resultant time series of sea ice drift allows to classify homogeneous sea ice drift fields and timing of their attachment to the landfast ice. In addition, the drift data allows to locate areas of formation of grounded sea ice accumulation called stamukha. This information сan be useful for local landfast ice stability assessment. The study is supported by the Russian Foundation for Basic Research (RFBR) grant 19-35-60033.</p>

scholarly journals Some engineering estimations of oil spill parameters in the marine environment

2018 ◽  
Vol 64 (2) ◽  
pp. 208-211 ◽  
Author(s):  
S. N. Zatsepa ◽  
A. A. Ivchenko ◽  
V. V. Solbakov ◽  
V. V. Stanovoy
Keyword(s):  
Oil Spill ◽  
Marine Environment ◽  
Oil Spills ◽  
Equations Of Motion ◽  
Ice Cover ◽  
The Arctic ◽  
Oil Flow ◽  
Ice Field ◽  
Drifting Ice ◽  
Similar Solutions

Estimation of the oil spill size at continuous spills on the moving sea surface or on the drifting ice field is the actual practical problem. Engineering estimation means the reduction of the hydrodynamic equations system to the balance of only two main forces that cause movement and resistance of the oil flow. From the simplified problem statement some practical relations were obtained for estimating the size of spill, including continuous oil spill with surface water currents presence, for spill onto porous snow-ice cover and onto the drifting ice cover. The obtained estimations can be used in more complicated models of oil spill transformation in the marine environment, primarily in the Arctic zone, and give basis for development of adequate responses on oil spills. The comparison of the obtained estimates with the self-similar solutions of the corresponding equations of motion of the spreading substance shows a satisfactory fit.

scholarly journals Wave climate and storm activity in the Kara sea

2020 ◽  
Author(s):  
Stanislav Myslenkov ◽  
Vladimir Platonov ◽  
Alexander Kislov ◽  
Ksenia Silvestrova ◽  
Igor Medvedev
Keyword(s):  
Interannual Variability ◽  
Pareto Distribution ◽  
Ice Cover ◽  
Wave Climate ◽  
Kara Sea ◽  
The Arctic ◽  
Storm Activity ◽  
Storm Waves ◽  
Ice Conditions

Abstract. Recurrence of extreme wind waves in the Kara Sea strongly influences the Arctic climate change. The paper presents the analysis of wave climate and storm activity in the Kara Sea based on the results of numerical modeling. A third-generation wave model WaveWatchIII is used to reconstruct wind wave fields on an unstructured grid with a spatial resolution of 15–20 km for the period from 1979 to 2017. The mean and maximum wave heights, wavelengths and periods are calculated. The maximum significant wave height (SWH) for the whole period amounts to 9.9 m. The average long-term SWH for the ice-free period does not exceed 1.3 m. The seasonal variability of the wave parameters is analyzed. The interannual variability of storm waves recurrence with different thresholds (from 3 to 7 m) was calculated. A significant linear trend shows an increase in the storm wave frequency for the period from 1979 to 2017. A double growth in the reccurence was observed for cases with an SWH more than 3–5 m from 1979 to 2017. The local maximum of the storm waves more than 3–4 m was observed in 1995, and the minimum in 1998. The maximum value (four cases) of the number of storms with an SWH threshold 7 m is registered in 2016. The frequency of wind speeds and ice conditions contributing to the storm waves formation were analyzed. It is shown that trends in the storm activity of the Kara Sea are primarily regulated by the ice. If the ice cover decreases in the southern part of the sea that leads to the increase of the number of events only with SWH threshold more than 3–4 m. If in the entire sea the ice cover decreases that leads already to increase of the extreme storms. The frequency of strong and long-term winds has high interannual variability and a weak positive trend. The analysis of distribution functions of the storm events with an SWH more than 3 m was carried out. Six different sectors of the Kara Sea were analyzed to reveal spatial differences. A comparison of the different distribution laws showed that the Pareto distribution is in the best agreement with the data. Up to 99 % of the points are described by this distribution. However, the extreme events with an SWH more than 6–7 m deviate from the distribution, and their probability is approximately twice as less as that predicted by the Pareto distribution. Presumably, this deviation is caused by the combined impact of rare wind speed frequencies and anomalies of the sea ice conditions.

scholarly journals Sea ice and the stability of north and northeast Greenland floating glaciers

2001 ◽  
Vol 33 ◽  
pp. 474-480 ◽  
Author(s):  
Niels Reeh ◽  
Henrik Højmark Thomsen ◽  
Anthony K. Higgins ◽  
Anker Weidick
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
Aerial Photographs ◽  
The Arctic ◽  
The North ◽  
Glacier Ice ◽  
Ice Conditions ◽  
Fast Ice ◽  
Break Up ◽  
The Stability

AbstractThe interaction between sea ice and glaciers has been studied for the floating tongue of Nioghalvfjerdsfjorden glacier, northeast Greenland (79°30’N, 22° W). Information from glacial geological studies, expedition reports, aerial photographs and satellite imagery is used to document the glacier front position and fast-ice conditions on millennial to decadal time-scales. The studies indicate that the stability of the floating glacier margin is dependent on the presence of a protecting fast-ice cover in front of the glacier. In periods with a permanent fast-ice cover, no calving occurs, but after fast-ice break-up the glacier responds with a large calving activity, whereby several years of accumulated glacier-ice flux suddenly breaks away. Climate-induced changes of sea-ice conditions in the Arctic Ocean with seasonal break-up of the near-shore fast ice could lead to disintegration of the floating glaciers. The present dominant mass loss by bottom melting would then to a large extent be taken over by grounding-line calving of icebergs. The local influx of fresh water from the north Greenland glaciers to the sea would be reduced and the local iceberg production would increase.

Problems Concerning Gravel Islands Constructing and Exploitation in the Arctic Conditions

2015 ◽  
Vol 725-726 ◽  
pp. 251-256
Author(s):  
Valeriya Efimova ◽  
Karl Shkhinek ◽  
Nikolay Belyaev
Keyword(s):  
The Arctic ◽  
Shallow Waters ◽  
Arctic Conditions ◽  
Drilling Operations

Drilling operations conducted from artificial islands are both feasible and economical in shallow waters. Accumulated experience in the construction and operation of artificial gravel islands are analysed. Capital protection of island’ slopes against the action of ice and waves are considered.

Holocene biomarker- and microfossil-based sea-ice reconstructions off the eastern North Greenland continental shelf (western Fram Strait)

2020 ◽  
Author(s):  
Nicole Syring ◽  
Ruediger Stein ◽  
Jeremy M. Llyod ◽  
Kirsten Fahl ◽  
Maximilian Vahlenkamp ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ice Cover ◽  
The Arctic ◽  
Future Climate Change ◽  
Time Interval ◽  
Fram Strait ◽  
The Holocene ◽  
Ice Conditions ◽  
Cyclic Changes ◽  
North Greenland

<p>Understanding the processes controlling the natural variability of sea ice in the Arctic, one of the most dynamic components of the climate system, can help to constrain the effects of future climate change in this highly sensitive area. For the first time, a detailed multi-proxy study was carried out to reconstruct past sea-ice variability off eastern North Greenland. This area is strongly influenced by cold surface waters and drift ice transported via East Greenland Current, meltwater pulses from the outlet glaciers of the Northeast Greenland Ice Stream, the build-up of landfast ice, and the formation of the Northeast Water Polynya. For our study, we have used well-dated sedimentary sections of Kastenlot Core PS93/025 and Gravity Core PS100/270. These sites are ideally suited to identify and disentangle the driving mechanisms of sea-ice distribution in the western Fram Strait. As proxies for the reconstruction of sea-ice cover we have used the sea-ice proxy IP<sub>25</sub>, a highly branched isoprenoid (HBI) monoene with 25 carbon atoms, in combination with specific open-water phytoplankton and terrestrial higher land plant biomarkers as well as specific microfossils (e.g., diatoms). Based on these high-resolution data sets we are able to reconstruct sea-ice variability, primary productivity, terrigenous input and seasonal formation of the NEW Polynya that evolved during the Holocene at the eastern North Greenland shelf.</p><p>The presence of IP<sub>25</sub> throughout the core PS93/025 confirms that there has been seasonal sea ice in the area during the entire Holocene time interval. Our biomarker proxies indicate relatively rapid changes in sea-ice conditions at ~9 ka and ~1 ka, i.e., sea-ice conditions progressed through three major stages over the course of the Holocene. During the early Holocene we recorded a reduced, but variable sea-ice cover. Between about 9.3 and 5.5 ka, sea-ice coverage increased towards seasonal conditions. Based on terrigenous biomarkers and IRD we assume a stronger regional than local sea-ice signal at core site PS93/025, due to the high influence of drift ice transported from the central Arctic Ocean along the eastern North Greenland shelf. During the late Holocene, especially during the last 1 ka, our records reflect the seasonal formation of the NEW Polynya leading to stable sea-ice edge conditions and a fully developed polynya situation. Probably, cyclic changes in the solar activity acted as trigger for the short-term variability in sea-ice cover during Holocene times.</p>

scholarly journals Tracing Atlantic Water Signature in the Arctic Sea Ice Cover East of Svalbard

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Vladimir V. Ivanov ◽  
Vladimir A. Alexeev ◽  
Irina Repina ◽  
Nikolay V. Koldunov ◽  
Alexander Smirnov
Keyword(s):  
Heat Flux ◽  
Time Series ◽  
Sea Ice ◽  
Ice Cover ◽  
Atlantic Water ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ice Thickness ◽  
Ice Concentration ◽  
Ice Conditions

We focus on the Arctic Ocean between Svalbard and Franz Joseph Land in order to elucidate the possible role of Atlantic water (AW) inflow in shaping ice conditions. Ice conditions substantially affect the temperature regime of the Spitsbergen archipelago, particularly in winter. We test the hypothesis that intensive vertical mixing at the upper AW boundary releases substantial heat upwards that eventually reaches the under-ice water layer, thinning the ice cover. We examine spatial and temporal variation of ice concentration against time series of wind, air temperature, and AW temperature. Analysis of 1979–2011 ice properties revealed a general tendency of decreasing ice concentration that commenced after the mid-1990s. AW temperature time series in Fram Strait feature a monotonic increase after the mid-1990s, consistent with shrinking ice cover. Ice thins due to increased sensible heat flux from AW; ice erosion from below allows wind and local currents to more effectively break ice. The winter spatial pattern of sea ice concentration is collocated with patterns of surface heat flux anomalies. Winter minimum sea ice thickness occurs in the ice pack interior above the AW path, clearly indicating AW influence on ice thickness. Our study indicates that in the AW inflow region heat flux from the ocean reduces the ice thickness.

scholarly journals Mechanics of oscillations and waves in the ice of the Аrctic ocean during compression and ridging

2020 ◽  
Vol 66 (3) ◽  
pp. 321-336
Author(s):  
V. N. Smirnov ◽  
S. M. Kovalev ◽  
A. A. Nubом ◽  
M. S. Znamenskiy
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Climate Models ◽  
Crack Formation ◽  
Friction Stress ◽  
Ice Cover ◽  
The Arctic ◽  
Dynamic State ◽  
Drifting Ice ◽  
Oscillations And Waves

One of the main scientific and practical problems in the Arctic is the study of the dynamic state of the sea ice cover. The main parameters in the general model of drifting ice are the drift velocity vector, friction stress at the air-ice and ice-water interfaces, and the forces of dynamic interaction of ice fields. Establishing the connection between the large-scale processes in the atmosphere-ice-ocean system is necessary for developing methods of forecasting ice compression and ridging and the formation of local and extended fractures and leads, which help improve the existing climate models. The main aim is to obtain results of full-scale instrumental measurements of parameters of ice large-scale mechanics and dynamics, which provide a physical basis for explaining the nature of observed large-scale ice processes and allow one to perform physical parametrization. To accomplish this aim and evaluate the physicomechanical condition of the drifting ice cover of the Arctic Ocean, the “Transarktika-2019” expedition performed a real-time ice monitoring in April 2019. The investigation was conducted using seismometers and tiltmeters installed on the ice such that they formed a triangle with the sides measuring up to two kilometers. Data has been obtained on the wave and oscillation processes of crack formation, compression and ridging of ice. The possibilities of deciphering the initial data on the physics of wave and oscillatory processes in the icewater system considerably increase when using the known methods of processing seismic signals. With use of spectral Fourier analysis wavelet-transformation of oscillations significanlty extending possibilities of the seismic method at revelation of prognostic signs of crack formation and compression was applied. It is shown that the dynamics of ice processes can be connected with oceanic swell and tidal events. A possibility is created for obtaining new results in the investigation of large-scale mechanics of sea ice.

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