A new type of ocean platforms is discussed in this paper. The uniqueness of this concept is that its hull is restrained such that any of the hull motions will be resisted by the axial stiffness of moorings. As a result, the platform is essentially motionless. Because of the superb motion characteristics, it can have many applications when a stationary platform is required, such as an oil producing platform in the partially ice-locked arctic environment or a host structure for wind turbines in deeper water.

Different kinds of offshore structures are designed and built to resist the scenarios of the arctic environment. This paper focuses on different ice load scenarios and the challenges for fixed offshore structures. Model test methods will be presented to assess the suitability of the design for the corresponding environmental scenarios. Measurement possibilities will be explained monitoring the design challenges as ice resistance, vibrations and encroachment of ice. The feasibility of different ice model test setups will be described and the main observations will be presented. The findings of the general phenomena of the resistance and encroachment will be discussed to assist the design process of offshore structures.

The Drake pipeline is located offshore Melville Island, in the Canadian High Arctic. It was built on-site in 1977-78 and connected to a natural gas production well, which operated for only a few months. The well was plugged in 1995 and the pipeline was abandoned. The pipeline extends from the shoreline to the wellhead located about one kilometer offshore to a water depth of 55 meters. It is buried at the shoreline crossing, to a target depth of 1.5 meters below sea bottom. A system to generate a frozen soil shield was also devised for further protection against drifting ice. Also, a berm made from ice and gravel was built at the water line. Field investigations could prove highly instructive to assess the state of the structure, and provide guidelines for design of future pipelines in high risks areas. However, significant technical and logistical challenges would face that venture, namely a ‘no physical contact’ (with the pipeline) restriction from the property owner, which leads to difficulty in understanding what has occurred to the pipeline beneath the soil, and a propensity for the region to be covered with a very thick ice cover.

This paper describes four case studies highlighting applications of Design of Experiments (DOE) methodology in ice basin testing. The case studies are (1) an investigation of methods for model ice ridge preparation and property testing, (2) managed first-year ridge interaction with an axisymmetric floater, (3) interaction of first-year ridges with a multi-leg GBS and (4) towing of a gravity-based structure and axisymmetric floater in ice. These experiments illustrate a different approach to ice basin testing. Rather than trying to reproduce natural conditions and scale up loads, critical design scenarios are isolated and DOE methodology is used to determine the most influential parameters on response quantities of interest.

In 2016 Nalcor Energy installed subsea cables across the Strait of Belle Isle, which comprises part of the Lower Churchill Transmission Project linking Muskrat Falls, Labrador, and Soldier's Pond, Newfoundland. The cable crossing site is southwest of a shoal which filters out deeper draft icebergs which could potentially contact and damage the cable. An initial study in 2011 was followed by iceberg tracking and current monitoring programs at the cable crossing site and a final study incorporating these data 2015-2016. This paper describes the application of a drift-based Monte Carlo model to assess iceberg risk to cables laid on the seabed in the Strait of Belle Isle. The model considers the effect of iceberg rolling which could potentially result in icebergs increasing draft and contacting cables laid on the seabed. Modeled iceberg drift was based on field observations, and measured and modeled currents. Based on results from the 2011 analysis it was decided to use directional drilling to route the initial portions of the cable from shore to break-put locations on the seabed in water depths in excess of 70 m. Rock dumping is used to stabilize the cables on the seabed at deeper water depths. Due to the extreme difficulties in trenching the very strong seabed or tunneling across the Strait of Belle Isle, the selected solution offers the most technically feasible and cost-effective solution for cable routing across the Strait of Belle Isle.

Recently turret-Moored FPSOs have been used in many deep water developments worldwide, with consideration of dis-connectable turrets for harsh environment with iceberg conditions. This trend makes the interactions between FPSO and risers system more important. Further, Steel Lazy Wave Risers (SLWR), which is a compliant variant of the mostly commonly used Steel Catenary Risers (SCR), is becoming an attractive riser option. The paper provides a review of two riser systems that can be considered for turret-moored FPSOs, and specific emphasis on Steel Lazy Wave Risers. A detailed case study of Steel Lazy Wave Risers for a typical turret moored FPSO with dis-connectable turret is presented. The design drivers are; to reduce the turret pay load, especially in disconnected condition, the selected riser system should have minimum tension variation so that the disconnected turret is stable and an optimum installed overall cost of the system. To achieve the design objectives an improvised Steel Lazy Wave Riser configuration called "Tethered Steel Lazy Wave Risers" (TSLWR) is developed. Pros and cons for TSLWR are discussed, with consideration of the particular challenges of turretmoored FPSOs with large floater motions, hang-off geometry constraints at turret, hang-off loads, riser interferences, risers pre-installation, and turret disconnection constraints.

The hydrocarbon reservoirs offshore North East Greenland are found in one of the most challenging environments in the world. Rigs will have to cope with, amongst others, short to non-existent open water seasons and large amounts of multi-year ice transported directly down from the North Pole, causing year around multi-year ice presence in the area. Several potential solutions for unlocking these reservoirs are being discussed, ranging from dedicated arctic rigs, to winterized and ice classed open water rigs. The paper will present an evaluation of four different rig designs comprising a turret moored arctic drillship, two winterized and ice classed open water drill ships and a winterized and ice classed drilling semi-submersible. The evaluation will address both the requirements to drilling operations offshore North East Greenland as well as the resulting capabilities for each rig design. In addition off-season usage possibilities will be addressed as part of the evaluation. The winterization and ice class requirements for the open water rig designs will be specified in a way which allows the rigs to operate offshore North East Greenland during the summer season. Capabilities of all designs will be determined on the basis of in house and publically available ice-load data. The consequential operability offshore North East Greenland will be determined on the basis of available ice data allowing for a comparison of the operational window lengths for the different units. As it is unlikely that any of the designs will be able to operate year around offshore North East Greenland in an economically attractive way, off-season usage possibilities will be evaluated as well, considering relevant areas in or near the Atlantic basin. The results of the offshore North East Greenland evaluation will be combined with the off-season usage possibilities in an overall comparison of the four rig designs. As a final result the paper will present a rationalized comparison between several potential solutions to unlock the hydrocarbon reservoirs offshore North East Greenland. As a consequence the paper eliminates to a large extent the subjective part in the design selection process for this specific application. Thus providing a valuable overview that has been missing until now.

Studies have suggested that the Arctic contains over 30% of the world's untapped natural gas reserves, and approximately 13% of its undiscovered oil reserves. The Beaufort shelf in the Canadian Arctic has been of interest for Oil and Gas development for many decades and reached a peak in the Mid 1980's when over 50 drilling islands were built to explore potential reserves by various international oil companies, with 92 wells recorded in the Canadian Beaufort Sea area. The Amauligak field was discovered in the Canadian Beaufort in 1984, and is still the largest oil and gas discovery in the Mackenzie Delta or Beaufort Sea areas. Amauligak lies approximately 75 kilometres northwest of Tuktoyaktuk in 30 metres water depth in the Beaufort Sea. The field is thought to contain 235 million barrels of oil and 1.3 trillion cubic feet of natural gas. Whilst vast resources such as Amauligak are known to exist in the Canadian Beaufort, the key to development of these remote areas is finding a viable export route for oil and natural gas. This was clearly the case for the development of the Prudhoe Bay Area of the Alaskan Arctic with the development of the Trans Alaskan Pipeline in the 1970's following the discovery of oil on Alaska's North Slope in 1968. This facilitated the development of the North Slope and shallow water offshore fields such as North Star which peaked in 1988 at about 738 million barrels per annum, about 25% of total U.S. production. Unlike the offshore shallow water Prudhoe Bay Developments, the development of the Beaufort shelf and slope will bring with it significant remoteness and geohazard issues as well as the familiar ice challenges. This paper highlights some of the geohazard issues facing Canadian Beaufort developments and considers what options exist for the safe and economical export of the product to market.

The ability of a drillship to maintain its heading to face oncoming pack ice is crucial under situations involving changes in pack ice drift direction. The performance of a vessel employing a Thruster-Assisted Mooring (TAM) system under such conditions is examined in this paper. Numerical simulations were used to determine the stresses and deformations within the moving pack ice cover, as well as the response of a drillship with characteristics similar to published information on Stena's DrillMAX. A turret mooring system is assumed to resist surge and sway direction offsets, but provides no restoring moment to vessel's yaw. In such system, thrusters would be used to provide damping and to apply the corrective moment that controls the heading of the vessel. The pack ice cover is assumed to consist of managed floes of sizes ranging from 30 m to 50 m, and with a uniform thickness of 1 m. The ice cover moves against the vessel at a steady velocity of 0.5 m/s. Simulations start with the vessel at a heading inclined to the oncoming ice direction. The simulations predict the evolution of the distributions of ice thickness and pressures, ice forces and moments, as well as the response of the vessel. Test cases examined a range of values of the initial heading of the vessel and limits on available yaw moment that can be generated by the thrusters. The results illustrate the manner in which the vessel can correct its heading, and give the corresponding offsets, ice forces and moments.

There are 32 arctic offshore oil/gas projects already in operation or having confirmed development plan. Seven offshore engineering patterns have been applied, including "gravity based structure (GBS) + shipping pipeline", "subsea production system + onshore terminal", "artificial island + shipping pipeline", "jacket platform +shipping pipeline + onshore terminal", "floating platform + subsea system", "FPSO + subsea system" and "offshore oil produced from land". Gravity based structure is the most widely used production platform, followed by FPSO/FSO, subsea production system, floating platforms and artificial islands. Arctic offshore wells have been mainly drilled from anti-ice floating drilling platform, ice-resistant fixed drilling platform and artificial island. In future, arctic petroleum exploration & production will move to deeper water area; natural gas development will play more important role. In arctic offshore E&P area Tremendous facilities and technologies will be developed and applied, including anti-ice floating concrete Spar, fully enclosed production platform, "subsea factory", round semi-submersible drilling platform, seafloor drilling rig, GBS LNG facility, free hanging solid ballast semi (FHSB Semi) platform and so on. Advantages & disadvantages, application conditions of main arctic offshore engineering patterns, facilities & technologies are described, which shall be helpful for arctic project investment opportunity study, screening and evaluation.

As the demand for energy resources continues to grow, the oil and gas industry is looking north to the Arctic for discovery and extraction of offshore hydrocarbon resources. In seasonal ice covered waters and regions frequented by icebergs where ice loads are significant; the Gravity Based Structure (GBS) has been shown, in cases, to be the preferred technically feasible solution (e.g. Hibernia, Hebron, Sakhalin 1, and Sakhalin 2). In remote locations, where there may be no pipeline infrastructure or the cost of such infrastructure may be too high, the GBS can be designed to offer storage at a reasonable cost. In some circumstances, a ballasted steel structure might have advantages over traditional steel reinforced concrete structures, as outlined in this paper. In these areas where ice loads are significant, the majority of installed Gravity Based Structures are comprised of steel reinforced concrete. This paper presents the concept of a steel GBS with a storage option for remote Arctic regions. The proposed structural design of the steel GBS is based on the study of ice loads and associated stability. The sizing, advantages and limitations of the unique hull structure are discussed in this paper. The paper discusses about the design and construction of a steel hull GBS capable of withstanding both first year ice and multi-year ice loads in an Arctic setting, where there is future proposed route for ice-class shuttle tankers. For the purpose of this paper, water depths between 30m and 50m are considered for the design of the structure. Optimized sizing of the GBS for various water depths, in order to achieve an approximate storage of six to eight days of crude oil production, is discussed.

The paper reports results of a feasibility study for the development of a multi-purpose submarine which could be applied to a variety of offshore operations sub-ice and in harsh weather areas. The study has jointly been carried out by ThyssenKrupp Marine Systems GmbH and Statoil ASA. Within the scope of the present study, a concept design for a submarine has been derived which can make a significant contribution to the successful development of arctic oil and gas projects. The versatile vessel is designed for several key missions. Installation, inspection, maintenance, and repair tasks for subsea facilities can be performed in water depths up to 1500 m by the use of an on-board gantry crane, an automatic storage system, and two work class ROVs. The boat can also be used to perform seabed seismic surveys at the same water depth. Furthermore the submarine offers unique abilities to respond to sub-ice oil and gas spills. The paper gives an overview of the vessel's layout, capabilities, main systems, safety features, and operational prospects.

In the nearshore zone of the Alaskan Beaufort Sea, three subsea pipeline bundles have been successfully installed by using conventional onshore construction equipment in the winter season operating from a thickened sea ice platform. Differences in water depth, route length and corresponding pipeline design for BP Northstar, Pioneer Oooguruk and Eni Nikaitchuq impacted the winter construction procedures used for each project. Each of these projects used the winter construction season to its maximum advantage, allowing the use of conventional and adapted onshore construction equipment and techniques. Comparatively, ice based winter pipeline construction in subarctic conditions has been generally less successful. On-ice pipeline fabrication and installation into a subsea trench has a track record for shallow water pipeline installation with reduced permitting issues compared to summer installation. Based on the experiences of these projects, this paper reviews the limitations of on-ice construction, the typical construction activities; the main equipment used and will highlight the main lessons learned.

This paper describes a simple mathematical model of hopper dumped dredge spoil dispersion that is based upon a modified version of Stokes’ law to estimate vertical particle velocities, and empirical metocean data to estimate horizontal particle velocities. The horizontal and vertical components are combined to simulate particle paths for computational packets of different grain size fractions under metocean conditions representative of those during the discharge period. Stokes’ law is modified using published relationships to account for large and non-spherical particles. Horizontal particle transport distance is controlled by water depth, particle size, current speed, and current direction variability based upon empirical metocean current speed and direction time series. The resultant dredge spoil depositional pattern is an irregular bull's eye in which particle size and deposit thickness decrease radially from the deposit center. Transport distances for each grain size fraction generally follow a lognormal-like distribution, with distances being inversely proportional to grain size. If there is a predominant current direction during disposal, the resulting deposit will be elongated in that direction. Application of the method, variations of which have been used to support dredge spoil discharge permit applications on several unnamed projects, is illustrated for a hypothetical site.

Abstract This paper presents the results of a study examining the feasibility of a Conical Piled Monopod (CPM) offshore Northern Alaska in about 41m water depth, fairly competent soil conditions, and Multi Year Ice environment. The study was conducted jointly by ConocoPhillips Company based in Houston, Texas and Granherne Ltd, a KBR Company based in Leatherhead, UK. ConocoPhillips sponsored the study. Two CPM concepts were considered, the Standalone CPM covered in this paper and a Dual Rig Jack Up (Gemini) Assisted CPM. The latter is the subject of another paper to be published later. The CPM was configured for two drilling rigs, assuming topsides weights ranging from 35,000 tonnes to 45,000 tonnes and corresponding operating weights from 60,000 tonnes to 70,000 tonnes respectively. Ice loads were calculated using ISO 19906 formulae where possible, otherwise using references within the ISO 19906 code and specialist ice load advice (Ken Croasdale) where necessary. The CPM has been shown to be feasible in the Alaskan Sea for the two ice conditions considered, 6m thick level ice and a very rare 25m thick ice island event. The ice island event represents a very conservative scenario and further data may allow its severity to be reduced. In addition, there will be many months, if not years, after discovery before an ice island can potentially impact the CPM. The CPM has a large enclosed volume available, which could accommodate a potentially significant amount of oil storage. However, this has not been quantified within this study work. The CPM concept eliminates or greatly minimizes the need for seabed preparation, being a pile supported structure. It also does not require solid ballast for resistance against sliding due to ice loads; these two characteristics of the CPM can have a major positive impact on the cost and schedule of an offshore Arctic project. ConocoPhillips has a Patent Pending on the CPM concept.

Abstract Five general categories of offshore structures incorporating granular material (‘islands’) have been utilized in the Beaufort Sea, primarily in the 1970's and 1980's. Although each concept has generally served its purpose, there have been many issues both during construction and during operations. This paper reviews the major issues by referring to three specific case histories. Introduction Five general categories of offshore structures incorporating granular material (‘islands’) have been utilized in the Beaufort Sea. Such ‘islands’ include sandbag retained islands, sacrificial beach islands, gravel islands (mainly in the U.S. Beaufort Sea), caisson retained islands and a water ballasted caisson on a berm. The majority of these structures, which total close to seventy, were constructed in the 1970's and 1980's. Apart from a few more recent production islands, these structures were primarily constructed to support exploratory drilling operations. Although the majority of these islands were in water depths less than 10 metres (approx. 30 feet) some hybrid islands have been successfully constructed in depths up to 31 metres (approx. 100 feet).

Abstract In offshore regions where risk of iceberg contact with subsea equipment is unacceptably high, protection options include reduction of the probability of impact by placing the equipment below the seabed in an excavation, and use of protective structures to reduce the probability of damage given an impact. An initial estimate of the probability of impact from a freely drifting or scouring iceberg may be determined based on the chance that an iceberg with draft greater than the top of the subsea equipment drifts directly over it. A more detailed analysis might consider the increase in probability of impact as a result of iceberg heave and pitch motions. In this paper, a methodology is presented for assessing the importance of heave motions of freely floating icebergs on probability of impact with subsea equipment protruding above the seabed. The method incorporates numerical and statistical modeling of random icebergs motions in irregular seas, including shallow water effects. Consideration is given to the mean clearance of the iceberg above the equipment, the random iceberg wave-induced heave motions, the geometries of the structure and iceberg and the time for the iceberg to pass over the site. Analyses are conducted on the effect of wave-induced heave motions of icebergs in wind-generated sea states and swell in water depths of 95 m and 60 m. A number of iceberg shapes are considered. It is found that for the conditions considered, heave motions do not have a significant influence on impact probability. In evaluating the previous methods for estimating wave-induced iceberg motions, some deficiencies in previous iceberg heave and surge response amplitude operators were discovered, and improvements are recommended when estimating iceberg impact loads with gravity based structures and floating systems.

Abstract Subsea pipelines located in ice environments need to be protected from potential ice gouging (also known as ice scouring) created when a moving ice keel interacts with the seabed. The integrity and operability of the pipeline can be affected by direct contact between the ice keel and the pipeline, or from loading imposed on the pipeline through soil deformation caused by ice gouging. The typical method considered for protecting against the risk of damage caused by ice gouging is through pipeline burial. Conventional methods of pipeline burial use equipment such as ploughs, mechanical trenchers, and jetters, the majority of which have been designed to accomplish a maximum of 2 to 3m of pipeline burial. Dredges can be used but they have water depth limitations and limited productivity. Land based equipment has been used for shore crossings, but is limited to shallow water depths where temporary construction berms can be used as a working platform. The capabilities of existing technologies are based on current industry practice developed for pipeline burial in ice free environments. Pipeline burial requirements have generally been for improved hydrodynamic stability, mechanical protection (e.g. from anchors), controlling pipeline movements (e.g. expansion and buckling) and/or for flow assurance purposes (reducing heat loss). A 2 to 3m burial depth has been generally adequate to satisfy these conventional requirements. As developments are proposed for areas that experience relatively deep ice gouging (up to 5m), burial depth requirements will exceed the capabilities of current pipeline burial technologies. New technologies capable of working in deeper water, achieving greater burial depths, achieving reasonable trenching advance rates, operating in harsh environments, and trenching through variable and difficult seabed soils will be required. This paper highlights the issues and challenges surrounding pipeline trenching and burial in ice gouge environments. Current state-of-practice is discussed along with the technology gaps that need to be addressed to prepare for future offshore developments in ice covered waters where there is the potential for seabed ice gouging.

Abstract Subsea structures on the seabed may be impacted by free-floating or scouringicebergs. A drift-based Monte Carlo iceberg contact model was developed as partof the SIRAM (Subsea Ice Risk Assessment and Mitigation) program forcalculating iceberg impact risk for subsea structures on the northeast GrandBanks offshore Newfoundland and the Makkovik Bank on the Labrador Shelf. Themotivation for developing this model was to characterize the influence ofbathymetry (i.e., seabed orientation, ridges and basins) on iceberg interactionrates with subsea structures. Results were incorporated into a GIS-basedapplication to allow iceberg contact rates to be calculated for structures witha range of plan dimensions and elevations at various locations.

Abstract Eighteen artificial (man-made) islands have been constructed in the AlaskanBeaufort Sea to support oil exploration and production. The first islands, constructed in the late 1970s, were in shallow nearshore waters where wave andice conditions are relatively benign. By the early 1980s, island constructionhad ventured to more exposed sites with water depths approaching 15 m. Innovative slope protection systems and construction methods were developed toaddress the remote Arctic locations, short construction seasons, scarce localresources, and the challenging, yet poorly defined, offshore wave and iceclimate. This paper provides an overview of the history of island developmentin the Alaskan Arctic and discusses design evolution, construction, andperformance.