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Platforms operating in arctic and subarctic regions such as the Grand Banks, Labrador Sea, Barents Sea and offshore Greenland are exposed to the risk of iceberg impacts. These structures must be designed to withstand the impact from an iceberg or be designed to disconnect and move offsite to avoid the impact. Offshore Newfoundland, gravity based structures (GBS) such as the Hibernia and Hebron platforms are designed to withstand an impact from an iceberg. However, current accepted practice is not to design the topsides for impact, but to reduce impact risk to an acceptable level by varying the facility geometry (i.e., topsides elevation or footprint).
An analytical model was developed to estimate the frequency of icebergs impacting the topsides using three dimensional (3D) models of the platform and the icebergs. Random shapes and sizes are simulated for each iceberg and 3D shapes are generated using a database of measured 2D iceberg profiles. The iceberg shapes are placed randomly in close proximity to the structure and are set to drift towards the structure in a straight line. The initial point of contact between the iceberg and the structure is determined. Crushing of the iceberg against the platform caisson is considered. The process is repeated a large number of times and the total number of contacts with the topsides are determined.
In 2012, Hibernia Management and Development Company Ltd. (HMDC) sponsored a field program in which high resolution iceberg profile data were collected. The high resolution iceberg profiles contain detailed 3D information of the above water and below water shape of the iceberg. This paper describes updates to the existing-topsides impact model to take full advantage of the detailed 3D iceberg profiles. These updates include new iceberg shape databases for simulation, and the addition of a detailed iceberg management model and a graphical user interface (GUI) to improve the functionality of the software.
This paper presents recent investigation results and geotechnical considerations used to design a manmade gravel island in support of offshore oil production in the Beaufort Sea off the coast of Alaska. Winter geotechnical investigations were conducted in 1997, 1998, 2013, 2014, and 2015 along multiple subsea pipeline alignments and several proposed island locations and included finding a gravel resource, analyzing sea ice safety, drilling boreholes, performing cone penetrometer tests, recording subsea ground temperatures, and laboratory testing to measure engineering properties of the soils. The results were used to characterize the geologic setting and permafrost conditions, estimate thaw settlement of the gravel fill and underlying permafrost, compressibility and strength of seabed sediments, island slope stability, and shear resistance to global ice forces. The island site is located in 20 feet of water with a finish elevation 15 feet above sea level for a total fill thickness of 35 feet. Total island surface settlement outside of the well row is estimated at three feet in the long term. A soft marine organic deposit underlies the island and critical slope stability conditions will occur during construction when steep subsea perimeter slopes are possible. Fill placement above the water line integrates a 30-foot setback from the edge of submerged fill to maintain minimum factors of safety and improve constructability. After consolidation and soil strength gain, the island stability factor of safety increases and long term ice pack loading and local wave scour management become more critical. Based on island geometry, seabed soil properties, and global ice forces, the island has an expected safety factor of 3.0 against shear failure. The results of the geotechnical investigations allowed permitting efforts to proceed by confirming conventional and proven island construction materials and methods can be used with some additional engineering considerations.
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.
Laurila, Pekka (ICEYE Ltd.) | Modrzewski, Rafal (ICEYE Ltd.) | Cheng, Tao (Exxonmobil Upstream Research Company) | Campbell, Brad (Exxonmobil Upstream Research Company) | Yanni, Victor Garas (Exxonmobil Upstream Research Company)
In 2015, ICEYE, a Finnish radar satellite company, with support by ExxonMobil Upstream Research Company, executed a series of field tests to assess the technical feasibility of using ICEYE's newly-designed Synthetic Aperture Radar (SAR) instrument for small ice feature detection in open water and pack ice imaging. The project consisted of three separate flight campaigns. The first campaign included calibration flights flown in Helsinki in March. The second campaign was performed in April, over sea ice in the Gulf of Bothnia. The third flight campaign, conducted in November, measured the performance of the instrument in weather.
In addition to validation of the designed SAR system, the main objective of the project was to obtain imagery of small ice features with the ICEYE prototype instrument. The analysis focused on the capability of the proposed SAR to detect small but potentially hazardous ice features. Two instrument configurations were used: a linear polarized antenna in VV configuration, and a circular cross-polarized antenna configuration. The reason for using a circular cross-polarized configuration in the SAR is that potential rain clutter can be reduced by suppressing odd-numbered reflections.
Test results from the ice measurement campaign showed that the linear VV configuration is sufficient for detecting features as small as 10 meters in waterline extension. On the other hand, small ice feature detection performance of the circular cross-polarized configuration was poor at transmitted power levels scaled to match the satellite case. Results also showed that sea state and target feature roughness play a significant role in detecting small features.
The third campaign was performed to understand whether rain clutter would affect the image quality with VV configuration, and whether such effects can be mitigated by a circular cross-polarized configuration. However, during the test period, only light to moderate rain conditions were encountered. In these conditions, the VV configuration suffered no rain clutter in levels affecting ice detection performance. A theoretical study concluded that in order for the rain clutter to interfere with imaging, the rain event must exceed levels that are extremely rare in arctic areas.
The flight test demonstrates that the ICEYE SAR data is valuable for ice management use. Once deployed in a constellation of small satellites, the resulting near-real time service can provide better situational awareness for potential operations in the Arctic.
Multi-year (MY) ridge and level ice interactions with sloping and conical structures involve complex ice feature shapes and ice failure mechanisms. The limited available field data makes calibration of associated load models difficult. To account for associated randomness and uncertainty, models may tend to be on the conservative side.
New deterministic algorithms were recently developed to calculate loads more accurately for interactions of MY level ice and MY ridges with an upward sloping structure. This paper presents the application of these recently developed formulations in a probabilistic framework using SILS. SILS is a Monte-Carlo type simulator developed by C-CORE following the general procedures outlined in ISO 19906. Ice and metocean input parameters are defined by the user either as a fixed value (e.g. friction coefficients) or a random distribution (e.g. ice drift speed, floe size). The yearly encounter frequency is first estimated for these ice features for the site of interest. The ice loads are then determined for each of simulated interaction event occurring over the model timespan, using the deterministic load formulations. By simulating a large number of years of ice interactions, design ice loads can be determined that correspond to various low annual probability of exceedances.
This paper demonstrates how complex loading scenarios, modelled in terms of idealized deterministic models, can be incorporated within a Monte-Carlo framework to provide design level loads. During the model implementation and analysis of results, significant improvements were identified and implemented in the deterministic model, resulting in a more robust model and better design estimates. The results provide valuable insights regarding model inputs and behaviour corresponding to the extreme design ice loads. An example of a full probabilistic analysis is presented in the paper to illustrate the models. Here the probabilistic framework of SILS is used to assess a Base Case scenario and a number of sensitivity cases using different environmental inputs and model parameters.
Power, D. (C-CORE) | Stuber, T. (C-CORE) | Rowsell, D. (C-CORE) | Zakharov, I. (C-CORE) | Fowler, C. (C-CORE) | Garas Yanni, V. (ExxonMobil Upstream Research Company) | Yi, X. (ExxonMobil Upstream Research Company) | Power, B. (Provincial Aerospace Limited) | Green, S. (Provincial Aerospace Limited) | Ryan, J. (Delta Radar Research Limited) | Hale, S. (Rutter Inc.)
In ice frequented regions, the potential for large ice floes and extreme ice features encroaching on offshore structures can be significant. An early warning system is desired to discriminate between thin ice of no risk and thick ice with significant challenge. The severity and variability of ice conditions will affect the feasibility of operating in such a region, with significant impact on the design and selection of resources to be used and the ice management requirements to support exploration and development. By measuring the ice thickness, operators can determine the operational risk for ice management operations. In addition, it can help map the areas of thin ice to aid shipping route selection. Despite its fundamental importance, sea ice thickness is one of the most difficult measurements to obtain via remote sensing. Passive remote sensing methods at the near infrared, thermal infrared and visible electromagnetic wavelengths, are restricted due to fog, precipitation, clouds, and Polar darkness. Thus active sensing techniques are deemed to be the only feasible method of measuring ice thickness, especially if they can be mounted in aircraft or satellites. Technical solutions are available to measure the thickness of sea ice, but they do not provide a physical measurement over a wide swath of ice. Thus, the authors are developing a wide swath ice thickness measurement system to fill this gap. The most practical solution for ice thickness measurement is an airborne radar. The authors have completed the preliminary design of a system that will combine an ice penetrating radar with a microwave synthetic aperture radar (SAR). The penetrating radar will be used to glean physical measurements of ice thickness, to be fused with the wide swath SAR to produce an ice thickness map.
Rahman, M. S. (Memorial University of Newfoundland) | Turnbull, I. D. (Centre for Arctic Resource Development) | Taylor, R. S. (Memorial University of Newfoundland and CARD) | Veitch, B. (Memorial University of Newfoundland)
This paper presents an analysis of the dynamics of ice, current, and wind based on the data collected on land-fast ice and ice floes from the offshore environment of Newfoundland and Labrador during April-August 2015 using satellite-tracked beacons. The beacons were deployed in three sets of three as follows: fast ice beacons (FIB) 2, 3, and 5 were deployed in a triangular array on the land-fast ice offshore Makkovik; fast ice beacons (FIB) 1, 4, and 6 were deployed in a triangular array on the landfast ice offshore Nain, and ice floe beacons (IFB) 7590, 1590, and 0650 were deployed on drifting ice floes offshore Makkovik. Ten ocean drifter beacons were deployed on May 22, 2015 in open water in the vicinity of ice floe beacons 1590 and 0650 to study the characteristics of surface ocean current dynamics. The drift velocities of the two ice floes have been compared with the wind velocities measured by the two weather stations deployed on the ice floes. The buoy drift rose and exceedance probability plots have been presented to analyze the dynamical characteristics of first year ice and ice floes in the offshore Labrador ice environment.
This paper reviews the use of intelligent chemical tracer technology that provides quantitative insight into the inflow distribution across the reservoir interval.
Arctic developments are frequently characterized by complex reservoir geology, challenging directional drilling requirements and complicated wellbore design. Understanding the permeability distribution that is encountered in these wells is key to optimizing the future well placement and field reservoir management decisions.
Assessing permeability distribution is best performed by measuring the reservoir inflow distribution under flowing conditions. Acquiring inflow distribution using conventional technologies, such as production logging tools, is very problematic in the arctic operational environment where wireline intervention into live wells is a major risk and cost.
Intelligent tracer technology provides insight into the inflow distribution without requiring any intervention into the well or major modification to the completion design. Unique chemical tracers are incorporated in polymers comprising an intelligent tracer system. These tracer systems are embedded into completion components during the manufacturing process. The completion components are assembled as part of the completion without any impact to normal operations. The components containing the tracer systems are placed at strategic locations along the completion interval.
Inflow from the reservoir contacts the intelligent tracers which release unique chemical molecules that can be detected at 1 part per trillion. Each of the tracers contain a unique molecule. The flow from the reservoir transports the molecules to the surface where samples of the well's production are acquired and analyzed for the concentration of each type of molecule. The concentration profile of each type of molecule is used to assess the inflow occurring at that location.
This capability can yield answers to very valuable reservoir management questions such as: Are all the intervals producing? What is the relative contribution of each interval? Where is water break-thru occurring?
Are all the intervals producing?
What is the relative contribution of each interval?
Where is water break-thru occurring?
Two independent mathematical models have been developed that provide the ability to quantitatively determine the reservoir inflow that is associated with the change in the molecular concentration. These models are referred to as the tracer arrival method and the flush out method.
This paper reviews how intelligent tracers work, laboratory testing to develop quantitative interpretation models and case histories that demonstrate the validity of the mathematical model.
Located 500 km north of the Arctic Circle, the massive Mary River Iron mine project required an operating ore dock to annually ship 3.5 million tonnes of iron ore to world markets. The high latitude Arctic ore dock loaded its first bulk carrier on August 8, 2015 from the its record breaking −17.75 m deep water berth. The project was executed by a design-build team selected by the owner after it became apparent the traditional design-bid-build method could not achieve schedule and budget objectives. Major challenges facing the design-build team included −35 degree celcius temperatures, 24- hour darkness, remote logistics, compressed schedule and varying geotechnical site conditions. To minimize risk in this challenging environment, the design-build team redesigned most of the project with a major focus on modularization of components in the south and utilization of a land-based construction methods rather than reliance on a fleet of marine equipment.