Currently, iceberg risk mitigation at production facilities in shallower waters (80 to 120 m) on the Grand Banks off the coast of Newfoundland and Labrador is accomplished using iceberg surveillance, towing, water cannons and, in the case of floating facilities, disconnection. Future developments in deeper waters such as the Flemish Pass or the Orphan Basin may be able to utilize compliant mooring and riser systems to allow a floating facility to simply move out of the path of an approaching iceberg without disconnecting. The analysis described here shows that, using simple extrapolation of the observed iceberg trajectory, the risk mitigation provided by facility side-tracking is comparable to existing physical management techniques (iceberg towing and water cannons). Improved short-term iceberg drift forecasting would allow further risk mitigation.

Approaches are presented in this paper for estimating the global mooring loads and response of a semi-submersible drilling rig, as a result of pack ice loading. The focus is on loading events from pack ice conditions relevant to the Grand Banks, where the pack ice typically consists of small floes and limited concentrations. The current practice for semi-submersible drilling operations on the Grand Banks is to avoid contact with pack ice by disconnecting and moving off-station in the event of an ice incursion. From a global loads perspective this may be unnecessary, given that the typical pack ice is of low severity and mooring loads may well be within acceptable limits. To be able to operate in pack ice while moored, operators need to demonstrate that the moored semi-submersible will have sufficient structural and mooring capacity to withstand the ice loads. Some existing semi-submersible hulls have ice strengthening in place as specified by a classification society, with associated allowable operating criteria in terms of ice conditions. These operating criteria are to ensure sufficient structural capacity given the ice conditions. No standardized approaches are currently available to quantify global pack ice loads and associated offsets for moored semi-submersibles, which are needed to assess the required mooring capacity. The objective of this paper is to address this gap and present approaches that can assist in specifying allowable operating criteria for station-keeping in pack ice.

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.

This paper examines the response of a drillship to the action of an ice cover undergoing a gradual change of direction of motion. For effective stationkeeping, the drillship must continuously change its heading to face the oncoming ice. The simulations consider a vessel that maintains position using Thruster-Assisted Mooring (TAM). A turret mooring system resists the surge and sway movements, while the thrusters act to correct the heading. The simulations of ice deformation and drift solve equations that describe conservation of mass and momentum, and a failure criterion. The drillship is treated as a three-degrees-of-freedom (surge, sway and yaw) rigid body. The results give distributions of ice drift, deformation and stresses around the vessel as well as the forces and offsets of the drillship. The resulting peak ice forces and moments on the drillship show clear dependence on the rate of change of ice drift direction. As may be expected, ice forces and moments increase for high rates. They also increase for higher ice velocities. Analysis of the results shows that the ratio of the length of the drillship to the radius of curvature of ice drift trajectories can be used to estimate ice forces and moments in an environment of changing ice drift direction. The present work additionally included a cursory examination of the effects of ice cover conditions; namely ice thickness and the existence of ridge fragments and icebreaking tracks, which are often formed as part of ice management operations.

The paper describes the technology challenges for year-round oil and gas production on 74°N in the Norwegian part of the Barents Sea. The northernmost blocks in the ongoing 23rd licensing round on the Norwegian Continental Shelf (NCS) are at 74°N and the physical environment in this area differs from other areas on the NCS where there are oil and gas production today. Firstly the paper briefly describes the physical environment in the Barents Sea, secondly it describes the technology challenges given year-round production. There are identified eleven key technologies which are enabling year-round oil and gas production in the Barents Sea. The technologies are grouped into which technologies that are considered necessary for enabling production, and which can enhance the production in either reducing CAPEX and OPEX or increasing production. All identified technologies have a relatively high technology maturity level. This means that in many cases technologies have already been applied other places in the world (e.g. Canadian Grand Banks) and could be adopted with minor modifications. In some other cases, technologies would have to be further tested at full scale before they could be applied.

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.

This paper presents a performance evaluation method of a floating, geo-stationary structure in sea ice. Using a turret-moored drillship as an example, the paper explains an approach to efficiently combine model-scale experiments and numerical simulations to analyze ice-structure interactions. A novel numerical simulation tool - Statoil's SIBIS model - is used to investigate the performance of the drillship concept in various design ice conditions. The presented method allows cost-efficient performance evaluations of ice-capable platforms throughout the early-phase design process, and leads to increased safety and commerciality of exploration operations in the Arctic.

Interaction between a moored structure and drifting broken ice is a complex process. To document the expected structure response, ice basin tests of the interaction are common practice. The outcomes of ice basin tests need to be carefully analyzed before extrapolation to expected full-scale target responses. The preferred strategy is to use numerical simulations to correct the measurements. The numerical model needs to be qualified by successful post-simulations of the achieved ice basin interactions. Post-simulations of interactions between drifting broken ice and a moored floating structure are of high complexity. The response of both the structure and the ice field needs to be replicated. This requires a good modeling of the ice field properties that matter (such as the floe size distributions and concentrations) and the boundary conditions affecting the interactions (such as the effect of the ice basin walls). Statoil's SIBIS numerical model is used to post-simulate ice basin tests of the moored Cat-I drillship. The present paper discusses the challenges with such post-simulations and presents the philosophy chosen for achieving successful postsimulations.

The combination of decreasing ice volume and thickness in Arctic regions results in extended activities of the oil and gas companies in these areas. Actually installed offshore structures are mostly fixed or moored ones. Problematic for moored structures especially with a turret position leading to an indifferent encounter angle is the heading of the vessel regarding the ice drift direction. That is why the idea was raised to combine moored offshore structures (such as FPSO's) with a dynamic heading control system. By such a system the heading can be adjusted to the optimal encounter angle of either waves or ice. Thereby the resistances especially due to changes of the ice drift direction shall be significantly reduced. The advantage of this system in comparison to a completely DP controlled vessel is, that the ice loads are mainly taken by the passive mooring system which does not need any fuel and is able to handle with high resistances while only the heading is controlled by the active thrusters. In case thrusters are installed at the front of the vessel which faces the ice, they may help to protect the turret, mooring lines and risers by their wash from ice contact. Additionally the vessel may operate independently in case of an emergency release of the turret due to critical ice loads on the mooring system. To investigate the benefits and challenges of moored and heading controlled vessel a new test set-up for ice model tests was developed at HSVA. The test set-up combines the already existing knowledge for moored structures with the recently developed DP system for model tests in ice. The DP system is a result of the recent research project DYPIC ( www.dypic.eu ) and is operating in a new designed mode which only controls the heading of the vessel. During testing the mooring system is simulated by lines leading from the turret to an underwater framework. The mooring characteristic (stiffness) is simulated by an individual combination of springs submerged and fixed on the framework. Above the water surface the model is tracked by an optical tracking system which is connected to the modified DP system. The optical tracking system and the submerged framework are fixed to the carriage. The ice drift is simulated by the movement of the towing carriage. The paper will describe the test set-up possibilities for the new test method as well as the experiences with the first ice model tests. Especially the challenges according to the modified dynamic heading algorithm shall be discussed. Based on analysis of the ice model test results the future work on the algorithm with regard to full scale vessels will be pointed out.

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.

The Arctic is the frontier area to securing energy supplies for the future. Finding oil and gas in the Arctic and subarctic regions is in itself challenging. Extracting the hydrocarbons in a safe and economical way, is considered possibly even more challenging due to extreme low temperatures, ice conditions, remoteness and a sensitive natural environment. The paper is based on ongoing development of a subsea separation and storage system for application in deepwater arctic. The paper describes solutions on how deepwater subsea separation of hydrocarbons and storage of oil can be achieved in hostile environments enabling close to continuous production also when surface production facilities has to abandon location. Overall arctic field development suggestions are presented based on the solutions.

Abstract The present paper addresses station-keeping in sea ice. Both design and operational measures are considered. Normative framework is reviewed and informative solutions to satisfy and document the requirements are presented. Introduction This paper concerns station-keeping in ice, with focus on design which relies on operational measures. Floaters in ice can generally be categorized as shown in Table 1, depending on how much ice and how many icebergs they are expected to meet during their operating life.

Abstract Recently the industry initiated 2 projects to address the issue of Arctic mooring systems. The first is an ABS study that includes a state of technology survey and an industry workshop for Arctic mooring systems. The ABS State of Technology Survey covers the topics of industry guidance and standards, ice loading predictions, current industry design practice, mooring hardware, and arctic operation philosophy. The ABS Industry Workshop has the objectives of providing a forum where industry experts could present their views and generate discussion, and to explore the need for a joint industry effort. At the end of the workshop, the general consensus indicated a need for a joint industry effort since the challenge is too big for any single company to meet. The second is a JIP organized by Kwan Engineering Services and Global Maritime to address the issues identified by the ABS industry workshop. It has the objectives of developing a design and operation practice document, and providing a forum for the industry and regulators to exchange information/ideas and work together to build consensus. The JIP has 6 tasks: mooring strength design practice, disconnect and reconnect devices, mooring hardware, global ice load prediction, ice management, and mooring installation. These studies indicate that current industry guidance and standards for mooring systems and Arctic structures are insufficient to address the design and operation of Arctic mooring systems. There are many challenging issues and disagreements to resolve. The Arctic mooring JIP initiated in 2013 has a large work scope and broad industry participation including operators, drilling contractors, designers, regulators, installation companies, and mooring component manufacturers. It is expected to produce a unified document based on rigorous investigations and consensus building, which will have a high impact on future Arctic mooring operations.

Abstract Drilling vessels and production platforms conducting oil and gas operations in the Arctic will need to keep station in drifting pack ice. A rapid and safe disconnection system is needed as ice loads can exceed the capacity of the mooring system used for stationkeeping. Connecting all lines to a disconnectable submerged buoy has been proven effective for this purpose in open water. Using a similar system for vessels/platforms operating in ice requires special considerations as the disconnection of the buoy may need to take place at high offsets due to the high magnitude of ice loads. There is no published work on the dynamics of submerged buoy for disconnection at high offsets. This paper presents new findings which were derived from numerical simulations for dynamic response of two disconnectable mooring buoy systems: a conventional medium size buoy with a compliant mooring system for a shuttle tanker in 200 m water depth (WD) and a larger buoy with a semi-taut mooring system for a drilling vessel in 500 m WD. Results for the global motion of the buoy and the dynamic contact loads between the buoy and the mating cone of the vessel soon after disconnect for various magnitudes of vessel offsets are presented in this paper. The results for the medium sized buoy with compliant mooring demonstrate strong nonlinear dependence of dynamic contact load on the disconnection offset in the range of 0 to 25% of the WD. The analysis results presented in this paper also show that a medium size buoy can have significant upward motion soon after exiting the mating cone and before it reaches its equilibrium position when the buoy is disconnected at high vessel offsets. For disconnections at very large vessel offset, the buoy during the upswing could impact the keel of an ice ridge. The large buoy with semi-taut mooring shows smaller upward motion for the 0 to 6% WD offset range considered in the simulations.

Abstract The increase of activities in oil and gas exploration and production in cold regions during the last years is associated with the development of new innovative concepts with respect to arctic fixed and moored offshore installations. As a consequence there is a huge demand from the oil industry to validate the proposed concepts and feasibility studies. Apart from that, Numerical simulations may be beneficial to a certain extent to investigate the ice related problems, one can still not dispense with the execution of physical model tests. Worldwide there are only a limited number of facilities available, which are able to cope with the challenge of ice model tests at a proper model scale. The paper describes broadly the assets and drawbacks of different types of mooring systems ("wet" or "dry" mooring system) and the choice of suitable substituted mechanical systems with respect to their application for various ice scenarios. Alternatives how to design the model test set-up in order to measure the ice forces independently from the system response forces of moored floating structures will also be discussed.

Abstract This paper is based on a study for a Barents Sea development with the objective to develop an Arctic deep water platform with the possibility to integrate oil storage that demonstrates the overall functionality of such a concept with regard to HSE, constructability, operability, maintainability and offloading capability. The design proposed is a CONDEEP™ Deep Floater platform consisting of a number of cylindrical concrete cells in clusters.

Abstract During the studies of ice loads on an Arctic Floater in ice, a series of numerical simulations were carried out in an advanced ship simulator with advanced ice module. The operation of the Arctic Floater will periodically be supported by an ice management system involving also physical ice management. This paper starts with introduction to the theoretical background for the Ice model, wherein the numerical model enables modelling of the arctic floater the mooring and different managed ice conditions. The managed ice is created as convex ice floes with comparable size ice floes used in model scale tests. A number of simulations were compared with and validated against results from identical set up in ice tank tests. Based on a set of assumptions from these simulations, a series of situations with varying ice drift direction, ice drift speed, floe thickness, domain size and ice floe coverage made the input parameters to the numerical model. Ice loading on the Arctic Floater is governed by ice breaking loads and ice transport around the hull. During the numerical simulations, the movement of the Arctic Floater was studied, the forces were calculated and influence of boundary conditions was investigated. The numerical simulations gave the possibility to compare ice floe interaction with and without boundary influence of an ice tank set up. Simulations was also used to show what would happen if the Arctic Floater is hit by a large unbreakable ice floe. The results presented in this paper show good correlation with model scale results for the Arctic Floater in drifting managed ice. Results from additional simulations gave useful input for predicting ice forces and system behaviour in ice conditions beyond what is possible in an ice tank test set-up.

Abstract Today's best engineering practice for the design of a stationary floating structure in ice infested water is articulated around physical testing in an ice basin and numerical modelling of the structure response to the relevant ice interactions. Ice basin testing is the best way to simulate the complex scenario of a moored floating structure interacting with drifting intact level ice and ridges. It is also per today the main source of experience for the design of such structures as full scale experience is sparse. However, ice basin testing suffers from deviations due to scaling effects or mismatch between one or several of the achieved and targeted properties (of the modelled ice and structure). As a consequence, the outcome of ice basin tests needs to be assessed and correction of measurements are required. An efficient way is to use an engineering numerical model to simulate the achieved ice-structure interaction in the ice basin, qualify the numerical model by comparing simulation results and measurements, and then simulate the targeted interactions with the numerical model. Such a numerical model may further be used to simulate the full range target design conditions for the ice structure interaction. The RITAS ice basin campaign tested a structure element designed to gain insight in the level ice bending and accumulation process around a traditional moored floating arctic structure design. These measurements are well suited to assess the validity of a numerical model designed to replicate this type of interaction. The SimShipIce numerical model is an engineering tool which focuses on replicating the steering processes during the interaction between a moored structure and drifting intact level ice and ridges. Such a model needs to be calibrated against ice basin test outcome.

Abstract Analysis of loads from icebergs for an Arctic Floater has been performed. The determination of iceberg loads was guided by the ISO 19906 International Standard. Global and local loads on the hull, as well as mooring loads, were studied. To determine loads at the specified levels of exceedance, probabilistic methodology using Monte Carlo methods was used, taking into account the areal density of the ice features (for example the number of icebergs per 10,000 km 2 ), and the probability distributions of the size and mass of the features, their added mass, their velocity, eccentricity of the collision, compliance of the structure, and the strength of the ice. The influence of surrounding sea ice on iceberg loads, as well as iceberg management including detection, towing and disconnection were analysed. Iceberg areal density was determined based on an analysis of available data, including information on the various forms, such as tabular or bergy bit. The strength of ice in collisions involving icebergs was modeled based on full scale crushing data from ship rams with multi-year ice. The pressure-area scale effects associated with ice-structure interaction were taken into account, considering also scatter in pressure measurements for a given contact area. Separate relationships for local and global loads were used. The analysis accounts for the Ekman current acting on an iceberg, together with wind and wave drift forces. Motions of the floating vessel and the icebergs in sea states were analyzed, accounting for the prevailing environmental conditions. Probabilities of collision along the length of the floater and in the vertical plane have been calculated using Monte Carlo methods. A variety of assumptions have been made: no ice management, management with and without disconnection, and the effect of sea ice on detectability and management is included.

Abstract The present work examines the loads on moored/DP-assisted drillships and their responses in managed pack ice. Numerical simulations are used to determine deformations and stresses within the ice cover and the movements of the vessel. The results give ice forces and moments on the vessel, as well as its surge, sway and yaw responses. The drillship assumed in this simulation work has a length of 230 m, a beam of 42 m, and a mass of 100,000 Mt. Simulations examine a case representing a moored vessel in a managed ice field consisting of 50 m floes that are 1 m in thickness, moving at a constant speed of 0.3 m/s. For ice moving along the surge direction, the peak surge force was approximately 2 MN. The corresponding maximum surge was 1.5 m. A parametric study further examines several aspects of ice interaction with the vessel. The results quantify various effects of ice management (the role of floe size), ice thickness and drift speed, the direction of ice movement, and stiffness of the mooring system. A case of combined mooring and thruster-assisted mooring is also examined. The additional contribution of the thrusters (or control of the DP system) is shown to somewhat reduce the offsets of the vessel. The work presents a methodology for evaluating the stationkeeping performance of vessels in managed pack ice and quantifying the role of the mooring/DP system characteristics.