Semi-submersible drilling platforms are typically moved off site given any threat of pack ice incursion. Operations in icy waters requires considerations of, amongst others, ice interations with the facility. The offshore industry will benefit from a standardized methodology to evaluate the capability of semi-submersibles in ice during drilling operations. Operators and drilling contractors are particularly interested in understanding how the drilling season may be extended into the shoulder season. This requires an understanding of variability in site-specific ice conditions throughout the year.
Ice load analysis is needed for semi-submersible rigs operating in ice prone regions to determine ice strengthening requirements. Ship-based ice class rules can be considered for the design loads of the pontoons in transit conditions, but there is no standardized methodology for determining ice loads for the operational conditions. This paper focusses on the operational phase, where loads act on the vertical-faced columns. ISO 19906 (2010) offers a framework for determining sea ice loads in the form of a deterministic equation that has been established for fixed structures mainly operating on a year-round basis. The results will generally be quite conservative for seasonal operations. Consideration of ice exposure, to account for the limited drilling season, is permitted by ISO 19906 using probabilistic approaches, though no specific guidance is provided. Seasonal operations can be planned to avoid the most severe winter conditions, allowing for a reduction of the design level ice conditions. This reduction in the severity of sea ice that impacts semi-submersible columns should be accounted for in determining design ice loads. This paper demonstrates application of an analytical approach to include exposure considerations to estimate extreme ice loads for various drilling season extensions.
An approach is demonstrated here for determining design sea ice loads to evaluate the capability of a semi-submersible in pack ice conditions. The approach considers the possibility of extended season drilling operations, rather than year-round operations, and may permit more efficient exploration in Arctic and sub-Arctic regions in the future. A study case is presented for a semi- submersible operating in the early ice season at a selected location in the Labrador Sea. The approach can be easily adopted for operations in other regions and other structure types, but is dependent on the availability of reliable data on ice conditions.
This paper will describe the design work and conversion work of icebreaker Otso from Baltic icebreaker to Polar class icebrekaer. Paper will include also user experience from the Arctic after the conversion work.
In April 2015 Arctia signed contract with one of the seismic companies which is operating in the Arctic and the conversion project for fulfilling the rules for worldwide trade and Arctic waters started. The schedule was very tight but all the modifications were made in time and the vessel was ready for Arctic operations in July 2015.
In order to increase vessel utilization outside of the Baltic icebreaking season Arctia Offshore have been studied different kind of solutions during the last ten (10) years. Numerous meetings and planning with naval architects, model tests in ice tank and open water tank was made and during the spring 2015 we had final plans what would be required in order to operate icebreaker Otso in the Arctic. Our requirement was that the open water behavior needed to be close to our multipurpose icebreakers Fennica/Nordica and modifications will not reduce icebreaking capability.
Icebreaker Otso was originally designed and classed to operate in the Baltic Sea in first year ice conditions and was not designed to do ocean passages. Using Otso in the Arctic has been restricted by open water characteristic, ice class and trade area (classification) restricted to domestic (Finnish, Baltic Sea) waters.
Modifications were performed by Rauma Marine Constructions at Rauma Shipyard and included:
New Flume tank to reduce rolling effect in open water conditions
Steel work in the hull, ice class upgraded
New lifeboats installed for worldwide operations standards
New helicopter deck for client use
New hospital for worldwide operations standards
SOLAS and 5 years docking according to the class regulations
Mezanine deck above the Flume tank was installed
Recycling station installed on Mezanine deck
Our experience is that now after three months operating in NE Greenland that the modifications we made are working. This investment was good example that old vessels can have new life and solutions are working. Cost save was massive compared to new build icebreaker.
This conversion shows that it is possible to increase utilisation of old icebreaker and a vessel can have new life
The Rapid Access Ice Drill (RAID) was designed and built to rapidly drill through the Antarctic ice cap, and then core the ice-rock transition zone and underlying bedrock. The system is designed to be mobile and to operate autonomously near the South Pole at elevations of 3000 to 4000 m and at air temperatures as low as −40°C. The anticipated drilling environment consists of about 100 m of firn that must be cased, followed by 2500 to 3300 m of glacial ice before reaching bedrock. The ice temperature at the surface is about −55°C warming to near 0°C at the base of the ice (warm ice). Previous work has focused on ice drilling and coring, and individual holes have required more than one drilling season. Our objective is to drill and complete a hole in approximately two weeks.
Firn will be drilled using a conventional auger system at 177.8 mm diameter until impermeable ice is encountered. Casing of 114.3 mm outer diameter will be placed in the hole and sealed against the ice with an inflatable packer. The next stage of drilling utilizes a 88.9 mm bit and 69.9 mm flush joint NRQ V-wall core rod to drill the ice section with penetration rates of 3 m/minute. The bottom hole assembly includes an outer bit and wireline-retrievable inner bit. After experimenting with a number of designs, we chose an outer bit with steel cutters to optimize penetration through the ice. In order to collect core in the transition zone or bedrock, the inner bit is removed by wireline and replaced with a coring assembly that utilizes an impregnated diamond bit.
The drilling system consists of five modules that will be mounted on skis for traversing the ice. These are a Drilling Rig Module, Rod Handling Module, Fluid Recirculation System (FRS) Module, a Power Module and a Shop/Inventory Module. The rig is a Boart Longyear LF-230 that we have modified to operate with an electric prime mover. The drilling fluid is ESTISOL-140 that is recycled through the FRS. The drilling system is powered by a 500 kW diesel generator. Two of these units are mounted in a power module to provide redundancy.
Wilton, Derek (Earth Sciences, Memorial University) | Feely, Martin (National University of Ireland) | Carter, James (Nalcor Energy - Oil & Gas) | Costanzo, Alessandra (National University of Ireland) | Hunt, Jon (National University of Ireland)
MLA-SEM analyses can quantitatively define the modal mineralogy of detrital components in a variety of sample material including offshore well cuttings such that the possible source(s) of the detrital material might be ascertained. The MLA data can be queried for combinations of detrital minerals that might reflect a specific source terrane (e.g., igneous suite, metamorphic complex,
AKAC participated in the full scale ice trials of the newly built R/V Sikuliaq, owned by the National Science Foundation and operated by the University of Alaska-Fairbanks. The purpose of the trials was to identify its ability to conduct science missions in ice, as well as to develop operational procedures for conducting independent science missions in ice.
This paper gives an overview of the key design features of the R/V Sikuliaq that enable it to conduct science missions in ice, as well as the observations and results from the full scale trials.
This paper provides real life experience on the operational performance of a state of the art research vessel. The experiences shared in this paper are applicable to a wide range of operations in ice, including station keeping in ice and towing in ice.
Lu, Wenjun (Norwegian University of Science and Technology) | Zhang, Qin (Norwegian University of Science and Technology) | Lubbad, Raed (Norwegian University of Science and Technology) | Løset, Sveinung (Norwegian University of Science and Technology) | Skjetne, Roger (Norwegian University of Science and Technology)
Sea ice concentration and thickness are important parameters for the calculations of ice actions and their effects on Arctic offshore structures and for the evaluation of icebreaker performance. Various methods exist nowadays to monitor these parameters, ranging from geophysical scale to local scale. During the Oden Arctic Technology Research Cruise 2015 (OATRC’ 15), we installed both Ice Concentration and Ice Thickness cameras and developed corresponding algorithms to achieve real time quantification of ice concentration and visual estimation of ice thickness information. For the ice concentration analysis, we utilized both the global Otsu method to categorize an image into two regions (black water and white ice); and the K-means method to identify more regions based on the gray scale from the image. With the methods, we conducted a case study by analyzing the ice concentration in a selected time window. In the case study, we include both dry ice (in white color) and wet ice (in gray color, generally composed of ice rubbles, young ice, and melt ponds) as ice region for the K-means method. The K-means method yields higher ice concentration values in comparison to the global Otsu method, in which, melt ponds/young ice was frequently mistaken as open water. It turns out that the K-means method enables more flexibility to cope with the complicated ice environment by separating the image into more regions that can be included as ice in an ice concentration analysis. For the ice thickness camera, the intention was to capture the events while a broken ice piece is tilted, next to the ship side, and expose its thickness region to the camera. In this paper, we developed an automatic tracking algorithm to sift these events out from all the images taken by the Ice Thickness acquisition system. After projecting a grid with physical length onto the image, the ice thickness information can be visually quantified. We compared the ice thickness obtained from the Ice Thickness camera and that obtained by an Electro-Magnetic inductive device in a selected time window. The results agree well with each other. Considering the advantages and disadvantages of each method, this demonstrates the benefits of combining redundant approaches for obtaining the ice thickness information with a higher degree of confidence.
This paper describes a study conducted to develop new capabilities for offshore geomagnetic surveying. To conduct the research we equipped two (2) new generation autonomous marine vehicles (AMVs) with towed marine magnetometers. This paper describes the validation study of the measurement system offshore between 2013 and 2015 that compares a regular pattern with main, tie and perimeter lines.
It was investigated whether the new AMV was suitable for use as a "base station" to monitor time variations of the disturbance field. The geomagnetic data measured by the vehicles from May 11 - 14, 2015 was analyzed and compared against data obtained from the USGS Honolulu Geomagnetic Observatory (HON). Highly sensitive sensors were used to establish the minimum required separation between the AMV and the magnetic sensor payload.
Directional drilling requires accurate knowledge of the geomagnetic field direction and strength in the wellbore. To compute wellbore azimuth, the measurement while drilling (MWD) tool takes a measurement of the magnetic field and then the directional driller compares it with the geomagnetic field reference in order to position the wellbore in real-time while drilling. By utilizing the AMV we were able to accurately map the crustal field direction and strength in the area of interest where the drilling activity for oil and gas will take place.
This study shows that the AMV is ideally suited to carry out geomagnetic surveys in offshore remote locations. Correction for the disturbance field is essential for crustal field mapping that requires a base station recording the variations of the disturbance field. A second AMV circulating at a fixed location provides a more accurate base station than a land-based station. This is due to two factors: The land- based station is further away from the measurement site and the disturbance fields are different on land than in the ocean, due to the different electrical conductivity of the subsurface.
The new generation AMV offers distinct advantages for data collection in offshore environments. Their low cost compared to seaborne or airborne vehicle allow them to be deployed in tandem and collect data repeatedly over predefined areas yielding accurate measurements to determine the disturbance and crustal fields. It solves the problem of accurately mapping the geomagnetic reference field in offshore locations that previously unknown of.
Exploitation of the Arctic's resources requires the mastery of the risks caused by extreme ice conditions. The design of offshore structures subjected to extreme ice conditions is a challenge for engineers since there are very few advanced design tools available on the market, especially those able to cope with the large variety of ice interaction and failure mechanisms.
Different approaches have been used to model and study ice behavior. Among them are analytical, numerical and empirical approaches with different models being considered. Each model has its own advantages and drawbacks and is only generally dedicated to certain circumstances. In 2012 Technip, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice
After three years, the first version of the Ice-MAS software (www.ice-mas.com) is now available. It simulates the ice loadings on a structure and the dynamic behavior of the drifting ice-sheet and floes around. Thanks to multi-agent technology, it is possible to combine in a common framework multiple phenomena from various natures and heterogeneous scales (drag, friction, ice-sheet bending failure, local crushing, rubble stack up) (
The Ice-MAS development program continues in 2016 with the addition of a capability to model the interaction of icebergs with offshore structures. This paper will introduce the co-simulation architecture proposed to simulate the complex interaction between an iceberg and a platform structure. It will focus on the hydrodynamic behavior of the platform and the iceberg including its stability. It will also consider the interaction between both bodies; including the non-linearity of the mooring system (in the case of a floating platform) and the local fracture mechanisms of the iceberg. The objective is to propose a new more accurate design method that will improve the overall ice management system for a project.
The paper examines ice compression (or pressure) build-up, which may pose a threat to navigation, over various zones of the Canadian Arctic and sub-Arctic waters. The results were obtained from a multi-year program conducted at the National Research Council of Canada. The objective of that program is to quantify the risks to navigation posed by compressive ice, and to develop predictive tools to aid shipping operations in an ice environment. The work consisted of a number of activities, including: the development of an ice dynamics model tailored for high-resolution simulations of ice cover drift and deformation; creating a database of besetting events and analysis of the conditions that influence the risk of besetting; hindcasting of ice and other environmental conditions that led to besetting over various geographic regions; and the development of forecasting tools to support offshore and shipping operations and training mariners. The present paper documents the governing equations of the ice dynamics and ridging model and discusses the high-resolution implementation that makes it possible to predict the risk of vessel besetting. A case of ice compression that took place in the southern Beaufort Sea is examined. The critical values of ice pressure and ridge thickness that posed a threat to vessels during that event were found compatible with estimates corresponding to besetting events in the Gulf of St. Lawrence and Frobisher Bay.
Lu, Wenjun (NTNU & Kvaerner) | Samardzija, Ilija (NTNU) | Lubbad, Raed (NTNU) | Sukhorukov, Sergiy (Kvaerner) | Hagen, Dagfinn (Kvaerner) | Rognaas, Gunnar (Kvaerner) | Østlund, Hilde Benedikte (Kvaerner)
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).