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 IMO's International Code for Ships Operating in Polar Waters (Polar Code) entered in to force on 1 January 2017 and provides, for the first time, an international regulatory framework for ships operating in Polar waters. In addition to technical regulations, the Polar Code requires that the Polar Ship Certificate should reference a methodology to assess operational capabilities and limitations in ice: essentially setting operational limitations for the specific ship navigating in Polar waters. The Polar Operational Limit Assessment Risk Indexing System (POLARIS) has been developed as an acceptable methodology for providing guidance on the operational limitations in ice of ships assigned different ice classes and has been directly referenced by the IMO in the Polar Code. The system was developed as a collaborative effort, drawing on operational and regulatory experience from industry and national administrations with experience in setting navigational limitations for ice covered waters. This paper presents the technical background behind the system and supporting information on its practical use both as a voyage planning tool and as real-time guidance on assessing ice regimes ahead of the ship. Validation of the system in the context of other existing regulatory requirements is discussed. The limitations of the system are explored and commentary and proposals are provided on recommended future enhancements.

Global ice loads at different locations on a ship during rams into ice are a function of ship motions and added mass in addition to the failure mode and strength of the ice. In the literature, various analytical added mass models have been used for ship-ice interactions, which could lead to significant differences in the prediction of global ice loads on ships. In this work, an improved added mass model has been developed based on numerical results and existing analytical models. Added mass coefficients of three ice-going ships, CCGS Amundsen, CCGS Louis S. St-Laurent and MVArctic , were estimated using four analytical added mass models. It was found that the differences in added mass coefficients predicted by these models are significant and enhancements can be made. A body-exact numerical simulation tool based on the potential-flow theory, MAPS0, has been used to compute the added mass coefficients of the three vessels in the frequency domain and the results were used for the development of the improved added mass model. The improvement in the load predictions has been demonstrated by applying the new added mass model to the three vessels.

Existing standards and codes do not comprehensively address and provide all necessary guidance and requirements for the design of Arctic offshore structures. Reliably assessing ice loads on offshore structures remains a challenge for industry, especially as "new" Arctic platform concepts are proposed for deployment in lighter ice operations, e.g. Arctic SEDU (Self- Elevating Drilling Units) and Arctic CSDU (Column-Stabilized Drilling Units). As a pragmatic solution, a comprehensive approach including relevant field measurements, physical model tests and numerical simulations is usually adopted in assessing the ice loads for a particular design. Field measurement results are limited in number and there is often uncertainty concerning actual ice conditions and load measurement techniques. Furthermore several data sets are constrained with proprietary restrictions. In particular no direct field data is available for the example "new" structures (SEDUs and CSDUs). Physical model tests always present challenges due to scale issues, ice property calibration, measurement uncertainties and high costs. Therefore, numerical simulations using the validated DEM tool based on the related field/model test data are anticipated to provide supplementary information for standards/rule-based designs. ABS has expended efforts to develop practical and advanced tools to assess the ice loads on offshore structures for several years. One promising numerical approach, a graphic processing unit (GPU) based Discrete Element Method (DEM) model, processes the computations in parallel and solves the DEM model with millions of particles for complicated ice-structure interaction problems, e.g. ice simultaneously loading on multiple legs and ice loading on a large CSDU. The paper presents details of the developing ABS GPU-DEM tool, status of the verification program, plans for the current and the future developments and applications. Included are brief descriptions of background technologies, an approach to derive the DEM model bonding strength inputs, and validation studies of ice breakage simulations based on the Bohai Bay Jacket ice data. The ice load simulations for fixed and floating structures, i.e. jack-up legs and the Kulluk floating drilling platform, are also shown to demonstrate the tool's capability and feasibility for Arctic offshore structure design. The interactions of ice and fixed/floating structures were analyzed, which provides useful references for future ice load modelling and offshore structure design.

With a series of physical model tests performed during February to August 2016, Arctic towing operation was investigated while towing a Gravity Base Structure (GBS) in managed sea ice with varying parameters: ice concentration, floe size, towing speed and towing configuration. The CONDRILL™ Arctic driller (Gravity Base Concrete structure) is a promising structural concept for extended exploration drilling operations in limited open water season and in harsh ice conditions. In the studies, the model-scale Arctic driller concept were constructed and tested in different paraffin-made model ice conditions. The tests, designed to shed light on both the physics and the practicalities of moving the GBS in varying ice conditions where towing force and structural stability, influenced by ice resistance are central for a successful platform design. The current model test is the first in a series where the results will be used as design input as well as subsequent marine operations employed for moving the platform in managed sea ice. This paper discusses initial assessments of towing force under varying ice conditions through physically modelling the most significant ice load contributor (i.e., the ice accumulation and clearing process). Based on the model tests, an optimum towing configuration, which involves no permanent ice jamming in all the tested ice conditions, was identified. In addition, it was found that for ice concentrations lower than 60%, the towing speed (or hydrodynamics) governs the towing resistance and the influence from ice floes are minor. However, while at high ice concentration (e.g., ≥70 - 75%), we are shifting from a hydrodynamics governed scenario into multibody dynamic interaction governed scenarios, in which, ice accumulation/clearing and internal friction resistance between the ice floes dominate the tow resistance. The study highlights the importance of an efficient ice clearing mechanism to release the pressure built-up in front of the structure and transport broken ice to the wake region of the structure, which results in lower resistance during towing. The studies reported in this paper contribute to the following items: 1) The multibody dynamic based physical modelling test would be the first of its kind to isolate this important physical process and to study it thoroughly without the influence from other physical processes such as sea ice fractures. 2) The test results are useful to validate currently available numerical simulation tools based on Discrete Element Method (DEM).

Wave driven iceberg and bergy bits’ impact load with an offshore structure is an important design concern. Hydrodynamic interaction between iceberg / bergy bit and an offshore structure in close proximity is an important factor that governs the impact load. Recently, a set of experiments has been conducted at Ocean Engineering Research Center (OERC) at Memorial University of Newfoundland to measure the wave loads on different sized spherical ice masses at different proximity to a fixed structure. A six component dynamometer was used to measure the loads in a quasi-static manner in six regular head waves. The objective was to investigate change in wave loads as the ice mass approaches to the structure. The experimental results show that the distance to wavelength ratio dictates the corresponding wave loads in horizontal and vertical directions. The mean drift force in the horizontal direction becomes negative (against the direction of wave propagation) for most of the cases when the body is close to the structure. Also, as the body is positioned closer to the structure, the non-dimensional RMS forces in the horizontal direction decrease and the non-dimensional RMS forces in the vertical direction increase.

The study of ice loads and associated mechanics is highly important in supporting oil and gas exploration and development in ice-prone offshore regions. While knowledge gaps regarding full details of the dynamic ice structure interaction process remain, substantial research is being carried out over a range of scales to improve understanding of excitation mechanisms for structures subjected to compressive ice loading. The present paper is focused on the first of a new series of medium-scale laboratory tests that have been carried out as a part of a larger program of research aimed at improving understanding of compressive ice failure phenomena and links between the formation of high-pressure zones and the occurrence of ice-induced structural vibrations under controlled conditions. The tests presented in this paper focus on the indentation of ice using a single spherical indenter mounted on a compliant beam system. Nine tests were performed to investigate the effect of ice temperature and indenter size on ice failure processes associated with high-pressure zone formation and evolution during dynamic ice crushing tests. Ice failure events were observed from regular and high-speed video synchronized with LVDTs and load cell data. Observations of ice load dynamics and structural response are discussed, along with corresponding observations of failure processes in the ice. In general it was observed that ice at warm temperatures was more prone to ductile type failure with lower, less dynamic pressures. By contrast, results from tests conducted at colder temperatures were characterized by a combination of spalling and crushing failure, which corresponded more with large-amplitude, sawtooth load cycles, which often resulted in load drop to zero as the rebounding structure cleared the failed ice from around the indenter. In terms of scale effects, it was observed for the same indentation rate and temperature, smaller indenters produced higher amplitude, higher frequency sawtooth loading than was observed for larger diameter indenters.

Abstract Ice-capable jackups can offer mobility and efficiency while drilling in shallow, ice-infested waters. However, the industry has limited experience operating jackups in ice environments, and technology gaps and uncertainties remain when assessing ice loads on multi-legged jackup units. The Graphic Processing Unit (GPU)-based Discrete Element Method (DEM) can be applied to investigate the degree of ice effects on multi-legged jackup units. In previous applications, the DEM method was used to simulate ice interaction with structures, but computations were limited to simple interactions. Introducing a GPU platform enables a substantial increase in the number of elements characterized so that the interaction of multi-legs and ice can be modeled with greater efficiency. For example, level ice modeled with 3-D bonded spherical elements can address the buoyancy, current effects and drag force encountered in harsh environments. Additionally, the parallel bonding approach and de-bonding criteria are used to model level ice freezing and breakage. In this investigation, the global ice loads on a jackup unit's single leg are analyzed to determine the effects of ice thickness, ice strengths and drifting velocities. The estimated ice loads are validated against full-scale data acquired from one application in Bohai Bay. Further, the mechanism of the interaction between the multiple legs and level ice is analyzed using the large-scale GPU-based simulation, the effects of sheltering and jamming are investigated and the ice loads simultaneously acting on the multiple legs are estimated to determine the total shear force and overturning moment.

Abstract There are large oil and gas resources in the shear zone region of theBeaufort Sea. Development of these resources would entail many factorsfor consideration. One of the most important is the ice load on drillingand production platforms. However, there is very large uncertainty on theice loads in this region due to a clear lack of knowledge of the pack icedriving forces. This pack ice driving force is one of the primarymechanisms that dictate how much force the ice can exert on an offshoreplatform, even if large multi-year ice floes are present. Improvedknowledge of this force would significantly reduce uncertainty in the designice loads, provide essential baseline engineering knowledge and a more reliablestructure, leading to greater regulatory certainty and safer and moreeconomical offshore operations. The pack ice driving force, as a function of width, can be calculatedthrough an equation in the ISO Arctic Offshore Structures Standard. However, a relevant parameter is still poorly defined for this equationand spans a large range. As a result, calculations of driving forces arevery uncertain, yet it is the key limiting force mechanism for the BeaufortSea. This paper presents the results of a study that investigated meansof refining uncertainty when calculating pack ice driving forces. Anoverview of the standard method of determining these forces is given, as wellas a discussion of the historical development of, and implications ofuncertainty in, calculating the pack ice force. Methods for refining theuncertainty are presented and comparisons are discussed. Numericalmodelling studies offer the greatest potential for refining the uncertaintybased on cost, usefulness, confidence in the results and studyopportunities. The information provided in this paper has applicationsfor refinement of pack ice driving force calculations in current engineeringstandards. A clear understanding of the magnitude of pack ice drivingforces would help to reduce the risk of failure of engineering structures andimprove their safety, by enabling a significantly better definition of theanticipated ice loads and the upper limit of the loads for the BeaufortSea.

Abstract The new international code ISO 19906 "Petroleum and natural gas industries - Arctic offshore structures" [1] was published in December 2010 after more than nine years of development. ISO 19906 uses the limit states design approach. Compliance is based on ensuring that the action effects arising from each factored action combination do not exceed factored resistances. The partial action factors have been calibrated to reliability targets. This paper describes the philosophy behind the quantification and use of the reliability targets, the definition of the limit states and action combinations, the philosophy of principal and companion environmental actions, and how the calibrated values of the action factors were incorporated in the action combinations. Introduction The new ISO 19906 has been developed in Working Group 8 (WG8) of ISO Technical committee TC67/SC7 "Offshore structures". Experts from all arctic nations and from most other nations involved in the design of offshore structures in arctic and cold regions participated in WG8. Consequently, all the arctic nations and all European nations have undertaken to adopt ISO 19906 into their sets of national standards, and ISO 19906 is expected to be adopted worldwide for design of arctic offshore structures. This paper explains the design approach and underlying structural reliability levels in order to assist with application of the code in different ice covered environments and regulatory jurisdictions. Reliability targets for arctic offshore structures have been used to calibrate the values of partial action factors for use in limit states action combinations, with particular focus on environmental actions arising from sea-borne ice, see Maes and Thomas [2] and OGP report 422 [3]. If these partial action factors are applied to Ultimate Limit State (ULS) and Abnormal (Accidental) Limit State (ALS) action combinations and the resulting action effects do not exceed factored resistances, the reliability targets are deemed to be achieved Reliability Targets "Reliability Target" as used in ISO 19906 is expressed as an annual probability of failure which is associated with global structural failure or with component failure leading to global structural failure. In common with the other ISO codes for offshore structures, namely ISO 19900 [4] and its associated standards, commonly known as the ISO 19900-series, ISO 19906 considers both life-safety and environmental protection through specifying three exposure levels, L1, L2 and L3, as defined in ISO 19902. [5].

Abstract This paper addresses the issue of Arctic standards covering past developments, present status, and future needs. The successful development of the Arctic is strongly dependent on the existence of adequate standards that insure the safety of this unique, pristine, and fragile environment. The national and international standards include those developed by classification societies (IACS members), governments (CFR's, CSA, BSI, NS), industry (API, NORSOK), and international organizations such as ISO/IEC and IMO. There have been significant efforts to harmonize requirements on the shipping side culminating in the development of; e.g., the IACS unified Polar Class requirements. A need exists for similar development for Arctic structures. The comparison between existing requirements for Arctic navigation and Arctic exploration drilling and production shows that significant differences exist and that there are important gaps that have to be bridged before the reliability of Arctic structures is assured. For example, the continued debate regarding the utilization of LRFD limit states philosophy and the magnitude of the load factors is still unsettled. Also there is a need for setting up principles for the definition of acceptance criteria when advanced analysis methodologies; now commonly employed in design of hull and component structures, are employed. The paper presents the results of the comparison and gap study performed and gives recommendations for the resolution of identified differences and the actions needed to mitigate the existing gaps Introduction The Arctic is probably the final frontier for oil and gas production. Table 1 shows recently published U.S. Geological Survey (USGS) estimates of undiscovered Arctic resources of oil, gas, and natural gas liquids in 33 Arctic provinces (USGS, July 2010, and 2009 and Gautier et. al., 2009). The total undiscovered resources amount to approximately 412 Billion barrels of oil equivalent (BOE) or 57 billion tonnes of oil equivalent (TOE) which is approximately 25% of the world undiscovered O&G reserves. For example, it has recently been reported (Rigzone 27 October 2010) that ExxonMobil has successfully drilled and tested the PTU-15 and PTU-16 development wells for the Point Thomson project, Figure 1, on Alaska's North Slope, ahead of the 2010 year-end target. Point Thomson is a remote natural gas and condensate field located on Alaska's North Slope, approximately 60 miles east of Prudhoe Bay. It is estimated to hold about 25 percent of the North Slope's discovered gas resources. Concurrent with the drilling of these two development wells, activities are also focused on engineering and environmental permitting which are critical for project development. To date, the Rigzone article states, about $1.5 billion, including more than $730 million in the last two years, has been invested in Point Thomson. The recent Gulf of Mexico Deepwater Horizon / Macondo oil spill disaster has proven that accidents do happen and the challenge is to be prepared for dealing with them. In the Arctic this will be the main challenge. Arctic challenges have been recently summarized in (Ghoneim, et. al., 2010), where twenty significant areas for research and development and regulatory issues have been identified. The availability of reliable standards for the planning, design, construction, installation, operation, and monitoring of Arctic drilling and production system is a major step towards attaining the goal of Arctic development.

Abstract The new ISO 19906 Arctic Offshore Structures standard contains provisions relating to a number of different types of offshore oil and gas structures in the Arctic and in other cold regions. Its provisions supplement those of ISO 19902 (steel offshore structures), ISO 19903 (concrete offshore structures), ISO 19904–1 (floating offshore structures) and other standards in the ISO 19900 series. This paper focuses on important arctic provisions and on how the standard can be used in conjunction with the other ISO offshore structures standards. Issues dealt with include features of arctic and cold regions; when the standard should be used; types of ice actions and how they should be applied; ice actions in the context of other physical environmental actions; manmade islands; subsea installations; ice data collection; monitoring; interpretation and analysis; ice management systems and operational aspects of arctic structures; and low temperature materials and equipment. Introduction Background Many of the structure design concepts used in arctic regions are similar to those in other areas and the same design principles apply. Nevertheless, the arctic environment poses a number of additional challenges due to marine icing on exposed surfaces, actions from sea ice and icebergs, structural vibrations as a result of ice actions, ice rubble encroachment, and brash ice build-up from icebreaker operations. In many cases, special operational procedures are required in harsh environmental conditions, which need to be factored into the designs. As a brittle solid, ice can exert considerable pressure over small contact areas, frequently exceeding average values over the loaded area. Local design requirements for ice are an integral part of the design process. It is because of the above issues that the ISO 19906 standard [1] was developed and, because their implementation can differ from standard practice, is why the present paper reviews its application. Terminology The ISO series has some particularities in terms of terminology with respect to North American usage. The main one is the use of the term "action" instead of "load", which is a more general term that could imply a load, an acceleration or a displacement. The characteristic value of an action or parameter is one that has a specified annual probability of being exceeded, which is often interpreted as a return period value. The representative value of an action is a characteristic value or some other value that is used for design.

Abstract This paper describes the results of a calibration of partial action factors in the new ISO 19906 Arctic Offshore Structures Standard. The work was scoped and directed by a panel of world experts in offshore Arctic engineering, constituted as ISO Technical Panel TP10 "Case studies and calibration". The calibration focuses on environmental action factors both for principal actions and for various environmental companion actions. The calibration is essentially a weighted risk-based optimization which targets three risk or exposure levels L1, L2 and L3 and which considers two limit states (ULS and ALS) as well as two basic sets of design check equations: a set I based on ISO 19902:2007 and a set II based on earlier suggestions in ISO/DIS 19906 and CAN/CSA-S471–04. It accounts for weighted combinations of all action effects in various proportions, for different resistance models, for different levels of action effect model uncertainties, for different levels of uncertainty, and for different mean action event occurrence rates. Weights used in the optimization were validated by the ISO panel TP10. Ice actions are regionalized on the basis of uncertainty characterization of extreme action effects (tails and extreme values). This is done with respect to both geographical region and type of structure. Regions with different ice action magnitudes can be considered together if their probabilistic description is similar. Four different calibration scenarios were considered for ice actions: a calibration of separate principal ice action factors for each combination of region and type of structure, a calibration of region-wide ice action factors, a calibration of one overall principal ice action factor, and the inclusion of ice actions in the larger group of all environmental actions. All four scenarios lead to reasonable action factors that are consistent with ice type and structure type. The multitude of environmental/ice companion factors in various environmental action combinations is reduced to just 4 companion action factors each of which is subsequently calibrated. Introduction The DIS version of ISO 19906 published early in 2009 contained normative clauses with respect to reliability, risk and consequences, but it did not provide definitive partial action factors for its limit states design framework. Accordingly, during 2009 a calibration was performed of the environmental action factors for exposure level L1 in order to ensure that the specified target reliability for each ULS and ALS action combination was achieved for circumstances that could reasonably be foreseen. A secondary objective was to also recommend calibrated environmental action factors for L2 and L3. A detailed report was published about the calibration in October 2009 (Maes, 2009). The present paper provides an overview of the analysis and the results of the calibration study. In addition to the above objectives, the report also provides detailed guidance on a recommended calibration method should the user of ISO 19906 wish to perform a site-specific or structure-specific calibration using a fully probabilistic approach. This objective is in itself quite important as ISO 19906 permits such an approach when the potential economic benefits of performing a site-specific calibration are likely to be considerable for large arctic offshore installations.

Abstract This paper presents the alternatives available and assessment of floating platforms, stationkeeping and riser systems based on studies undertaken for Arctic fields. The industry experience with floating units for both drilling and production operations in the offshore areas subjected to ice features are discussed. The salient aspects of these systems are discussed considering the general characteristics of selected basins. The Arctic fields developed so far are in water depths up to 125 m and have used the Gravity Based Structures and detachable FPSOs, besides other systems such as jacket platforms and islands used in shallower water. There is significant industry interest in the development of Arctic and Sub-Arctic fields in water depths beyond commercial viability of bottom founded designs. The water depths in some North American and offshore Greenland Basins are up to 2,800 m. The development of fields in deeper water would require use and adaptation of floating units and subsea systems, which have been used in many deepwater basins. However, their use in deepwater Arctic would add significant challenges from harsh weather, severe ice features (pack ice, icebergs), lack of infrastructure, remoteness, and reduced accessibility. The floating unit designs, alternatives for sub-systems, and subsea solutions and technologies are enabling development of Arctic fields offshore Norway and Russia, such as Goliat and Shtokman in up to 350 m water depth. Floating units provide flexibility in field development and ability to detach and move the unit from the path of significant ice loading events and icebergs. These features enable improve their technical and commercial feasibility by reducing load effects and risks. Challenges in Arctic The development of hydrocarbon fields offshore Arctic and Sub-Arctic in the North, have gained significant importance due to potential for very large reservoirs increasing their commercial viability. Some of the important leasing areas in the Arctic or Sub-Arctic offshore identified in Fig. 1 are in deepwater and ultra-deepwater: Barent Sea, offshore Norway and Russia; Orphan Basin, offshore Newfoundland; and fields offshore Greenland and Iceland. The water depths vary from 300 m to 3,000 m in these leases and several of these fields are in exploratory drilling or in the development planning stages.