3.2 Specifications for a subsurface ice intelligence system
26
3.2 Specifications for a subsurface ice intelligence system
26
3.2 Specifications for a subsurface ice intelligence system
26
3.2 Specifications for a subsurface ice intelligence system
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1 Copyright © 2009 by ASME
Proceedings of the ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31-June 5, 2009, Honolulu, Hawaii, USAOMAE2009-79606
Specifications for a subsurface ice intelligence system
Kenneth Eik
Statoilhydro
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwaySveinung Løset
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwayABSTRACT
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. An ice intelligence system is one of several required elements in an IM system. This paper presents possible solutions for Subsurface Ice Intelligence Systems (SIIS). Capabilities of technology for sonars, unmanned underwater vehicles, and communication nodes are highlighted and need for further development is commented.
KEY WORDS
Ice management, ice intelligence, sonar, UUV
1. INTRODUCTION
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. In general, IM includes all activities where the objective is to reduce or avoid actions from any kind of ice [1]. Such activity may include ice detection, tracking, forecasting, threat evaluation, ice breaking, iceberg towing etc.. An ice intelligence system is one of several required elements in an IM system. The ice intelligence system has to ensure that all information regarding ice conditions, that might influence marine operations, is collected and presented for relevant personnel in due time. For ice intelligence, typically surface scouting tools such as satellites, airborne recognizance, marine radars, drift buoys and visual observations from icebreakers have been used. All these methods may be limited by the weather conditions. SAR
images from satellites, that are unaffected by the weather, are also limited by the trade off between spatial coverage and resolution. With respect to airborne recognizance and deployment of drift buoys, there is generally some degree of risk for the personnel involved in these operations.
Considering that the ice characteristic is more distinct under water, the development of a Subsurface Ice Intelligence System (SIIS) seems to be a promising subject for future technology focus. This paper presents two possible systems for subsurface ice intelligence and describes the type of instruments that are needed and the requirements these instruments must fulfill. The proposed specifications will be relevant for water depths in the range 100 to 300 m. Existing technology has been reviewed and evaluated towards the different requirements of the SIIS. Further, a discussion regarding the feasibilities of the systems has been included.
Finally, some conclusions are drawn regarding the applicability of the SIIS.
2. PROPOSALS FOR SUBSURFACE ICE INTELLIGENCE SYSTEMS
2.1 Acoustic Fence
Both exploration and production drilling will usually involve some sort of structure or vessel, either moored or dynamic positioned at a fixed location. The structure must either be able to withstand the actions from all ice features in the area or be able to escape location if ice loads are assumed
28
1 Copyright © 2009 by ASME
Proceedings of the ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31-June 5, 2009, Honolulu, Hawaii, USA
OMAE2009-79606
Specifications for a subsurface ice intelligence system
Kenneth Eik
Statoilhydro
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwaySveinung Løset
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwayABSTRACT
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. An ice intelligence system is one of several required elements in an IM system. This paper presents possible solutions for Subsurface Ice Intelligence Systems (SIIS). Capabilities of technology for sonars, unmanned underwater vehicles, and communication nodes are highlighted and need for further development is commented.
KEY WORDS
Ice management, ice intelligence, sonar, UUV
1. INTRODUCTION
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. In general, IM includes all activities where the objective is to reduce or avoid actions from any kind of ice [1]. Such activity may include ice detection, tracking, forecasting, threat evaluation, ice breaking, iceberg towing etc.. An ice intelligence system is one of several required elements in an IM system. The ice intelligence system has to ensure that all information regarding ice conditions, that might influence marine operations, is collected and presented for relevant personnel in due time. For ice intelligence, typically surface scouting tools such as satellites, airborne recognizance, marine radars, drift buoys and visual observations from icebreakers have been used. All these methods may be limited by the weather conditions. SAR
images from satellites, that are unaffected by the weather, are also limited by the trade off between spatial coverage and resolution. With respect to airborne recognizance and deployment of drift buoys, there is generally some degree of risk for the personnel involved in these operations.
Considering that the ice characteristic is more distinct under water, the development of a Subsurface Ice Intelligence System (SIIS) seems to be a promising subject for future technology focus. This paper presents two possible systems for subsurface ice intelligence and describes the type of instruments that are needed and the requirements these instruments must fulfill. The proposed specifications will be relevant for water depths in the range 100 to 300 m. Existing technology has been reviewed and evaluated towards the different requirements of the SIIS. Further, a discussion regarding the feasibilities of the systems has been included.
Finally, some conclusions are drawn regarding the applicability of the SIIS.
2. PROPOSALS FOR SUBSURFACE ICE INTELLIGENCE SYSTEMS
2.1 Acoustic Fence
Both exploration and production drilling will usually involve some sort of structure or vessel, either moored or dynamic positioned at a fixed location. The structure must either be able to withstand the actions from all ice features in the area or be able to escape location if ice loads are assumed
28
1 Copyright © 2009 by ASME
Proceedings of the ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31-June 5, 2009, Honolulu, Hawaii, USA
OMAE2009-79606
Specifications for a subsurface ice intelligence system
Kenneth Eik
Statoilhydro
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwaySveinung Løset
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwayABSTRACT
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. An ice intelligence system is one of several required elements in an IM system. This paper presents possible solutions for Subsurface Ice Intelligence Systems (SIIS). Capabilities of technology for sonars, unmanned underwater vehicles, and communication nodes are highlighted and need for further development is commented.
KEY WORDS
Ice management, ice intelligence, sonar, UUV
1. INTRODUCTION
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. In general, IM includes all activities where the objective is to reduce or avoid actions from any kind of ice [1]. Such activity may include ice detection, tracking, forecasting, threat evaluation, ice breaking, iceberg towing etc.. An ice intelligence system is one of several required elements in an IM system. The ice intelligence system has to ensure that all information regarding ice conditions, that might influence marine operations, is collected and presented for relevant personnel in due time. For ice intelligence, typically surface scouting tools such as satellites, airborne recognizance, marine radars, drift buoys and visual observations from icebreakers have been used. All these methods may be limited by the weather conditions. SAR
images from satellites, that are unaffected by the weather, are also limited by the trade off between spatial coverage and resolution. With respect to airborne recognizance and deployment of drift buoys, there is generally some degree of risk for the personnel involved in these operations.
Considering that the ice characteristic is more distinct under water, the development of a Subsurface Ice Intelligence System (SIIS) seems to be a promising subject for future technology focus. This paper presents two possible systems for subsurface ice intelligence and describes the type of instruments that are needed and the requirements these instruments must fulfill. The proposed specifications will be relevant for water depths in the range 100 to 300 m. Existing technology has been reviewed and evaluated towards the different requirements of the SIIS. Further, a discussion regarding the feasibilities of the systems has been included.
Finally, some conclusions are drawn regarding the applicability of the SIIS.
2. PROPOSALS FOR SUBSURFACE ICE INTELLIGENCE SYSTEMS
2.1 Acoustic Fence
Both exploration and production drilling will usually involve some sort of structure or vessel, either moored or dynamic positioned at a fixed location. The structure must either be able to withstand the actions from all ice features in the area or be able to escape location if ice loads are assumed
28
1 Copyright © 2009 by ASME
Proceedings of the ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31-June 5, 2009, Honolulu, Hawaii, USA
OMAE2009-79606
Specifications for a subsurface ice intelligence system
Kenneth Eik
Statoilhydro
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwaySveinung Løset
Norwegian University of Science and Technology (NTNU)
Trondheim, NorwayABSTRACT
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. An ice intelligence system is one of several required elements in an IM system. This paper presents possible solutions for Subsurface Ice Intelligence Systems (SIIS). Capabilities of technology for sonars, unmanned underwater vehicles, and communication nodes are highlighted and need for further development is commented.
KEY WORDS
Ice management, ice intelligence, sonar, UUV
1. INTRODUCTION
In connection with offshore activities in waters exposed to sea ice and/or icebergs, ice management (IM) systems need to be applied. In general, IM includes all activities where the objective is to reduce or avoid actions from any kind of ice [1]. Such activity may include ice detection, tracking, forecasting, threat evaluation, ice breaking, iceberg towing etc.. An ice intelligence system is one of several required elements in an IM system. The ice intelligence system has to ensure that all information regarding ice conditions, that might influence marine operations, is collected and presented for relevant personnel in due time. For ice intelligence, typically surface scouting tools such as satellites, airborne recognizance, marine radars, drift buoys and visual observations from icebreakers have been used. All these methods may be limited by the weather conditions. SAR
images from satellites, that are unaffected by the weather, are also limited by the trade off between spatial coverage and resolution. With respect to airborne recognizance and deployment of drift buoys, there is generally some degree of risk for the personnel involved in these operations.
Considering that the ice characteristic is more distinct under water, the development of a Subsurface Ice Intelligence System (SIIS) seems to be a promising subject for future technology focus. This paper presents two possible systems for subsurface ice intelligence and describes the type of instruments that are needed and the requirements these instruments must fulfill. The proposed specifications will be relevant for water depths in the range 100 to 300 m. Existing technology has been reviewed and evaluated towards the different requirements of the SIIS. Further, a discussion regarding the feasibilities of the systems has been included.
Finally, some conclusions are drawn regarding the applicability of the SIIS.
2. PROPOSALS FOR SUBSURFACE ICE INTELLIGENCE SYSTEMS
2.1 Acoustic Fence
Both exploration and production drilling will usually involve some sort of structure or vessel, either moored or dynamic positioned at a fixed location. The structure must either be able to withstand the actions from all ice features in the area or be able to escape location if ice loads are assumed
28
2 Copyright © 2009 by ASME to exceed the design criteria. Icebreakers or iceberg towing
vessels may be used in order to reduce or avoid actions from the ice.
Generally, ice may approach the structure from all directions.
Sudden changes in ice drift direction are generally known to be difficult to predict unless there is a strong dominance by the tidal currents. Hence, it is proposed that ice conditions are monitored in a continuous circle around the structure (Figure 1).
Figure 1. Configuration of eight sonars around an installation.
R is the preferred distance from installation to the fence while L is the required footprint length for one sonar. Red dots
indicate where the sonars should be located.
2.1.1 Multi Beam Sonars. An acoustic fence can
be achieved by deploying a number of multi beam upward looking sonars arranged in a circle around the structure (Figure 1). The sonars are used to determine the distance from the sonar to the bottom of the ice surface. If Acoustic Doppler Profilers (ADPs) are installed in the same rigs as the sonars, parameters such as ice thickness, ice drift speed and ice drift direction can be monitored.
The preferred solution is to cover a continuous circle around the operating structure (Figure 1). In the Barents Sea and at the Grand Banks, the average ice drift speed is reported to be around 20 cm/s while it can be slightly higher than 1 m/s in more extreme situations (valid for both sea ice and icebergs) [2,3]. Assuming that a drilling operation will need at least 30 minutes
1to safely disconnect and leave drilling site, ice features must be identified and managed when they are at least 1.8 km away from the structure in the extreme case.
1 The time it will take to close down operations and prepare for disconnect will depend on a number of factors. The proposed value of 30 min should be considered as a minimum for most types of operations. Further, an ice intelligence system that not provides at least 30 minutes warning would be considered disqualified for Ice Management operations.
The required footprint length in the water line for each sonar will depend on the water depth as well as the radius in the alarm circle. For practical reasons, the required number of sonars must be kept at a minimum level. Since the sonars are indented to cover a circle, it is important that the footprint length is maximized. In order to capture the most important details in the underwater ice sheet, a resolution around 1 x 1 m within the entire footprint seems reasonable.
This requires instruments that have a significant coverage and excludes devices such as single beam sonars. By applying multi beam sonars and in addition mount them in a tilted orientation, as shown in Figure 2, a fairly long footprint may be achieved for a given water depth. However, the resolution will not be uniform within the footprint and due to this; there will be a trade off between resolution and coverage.
Figure 2. Illustration showing a multi beam sonar installed
tilted in a frame.
To cover a circle with radius 1.8 km with eight sonars, the footprint under the ice must be at least 1.4 km long for the extreme ice drift events (Figure 1).
Table 1 shows the required length of the footprint for some other possible combinations of ice drift speeds and number of instruments. The requirements with respect to width of the footprints are however, less strict. If sonar scans are available every minute, ice drifting with speed 1 m/s will move maximum 60 m between each scan. This means that a footprint width of 60 m is sufficient to capture all ice features passing the sonar.
29
2 Copyright © 2009 by ASME
to exceed the design criteria. Icebreakers or iceberg towing vessels may be used in order to reduce or avoid actions from the ice.
Generally, ice may approach the structure from all directions.
Sudden changes in ice drift direction are generally known to be difficult to predict unless there is a strong dominance by the tidal currents. Hence, it is proposed that ice conditions are monitored in a continuous circle around the structure (Figure 1).
Figure 1. Configuration of eight sonars around an installation.
R is the preferred distance from installation to the fence while L is the required footprint length for one sonar. Red dots
indicate where the sonars should be located.
2.1.1 Multi Beam Sonars. An acoustic fence can
be achieved by deploying a number of multi beam upward looking sonars arranged in a circle around the structure (Figure 1). The sonars are used to determine the distance from the sonar to the bottom of the ice surface. If Acoustic Doppler Profilers (ADPs) are installed in the same rigs as the sonars, parameters such as ice thickness, ice drift speed and ice drift direction can be monitored.
The preferred solution is to cover a continuous circle around the operating structure (Figure 1). In the Barents Sea and at the Grand Banks, the average ice drift speed is reported to be around 20 cm/s while it can be slightly higher than 1 m/s in more extreme situations (valid for both sea ice and icebergs) [2,3]. Assuming that a drilling operation will need at least 30 minutes
1to safely disconnect and leave drilling site, ice features must be identified and managed when they are at least 1.8 km away from the structure in the extreme case.
1 The time it will take to close down operations and prepare for disconnect will depend on a number of factors. The proposed value of 30 min should be considered as a minimum for most types of operations. Further, an ice intelligence system that not provides at least 30 minutes warning would be considered disqualified for Ice Management operations.
The required footprint length in the water line for each sonar will depend on the water depth as well as the radius in the alarm circle. For practical reasons, the required number of sonars must be kept at a minimum level. Since the sonars are indented to cover a circle, it is important that the footprint length is maximized. In order to capture the most important details in the underwater ice sheet, a resolution around 1 x 1 m within the entire footprint seems reasonable.
This requires instruments that have a significant coverage and excludes devices such as single beam sonars. By applying multi beam sonars and in addition mount them in a tilted orientation, as shown in Figure 2, a fairly long footprint may be achieved for a given water depth. However, the resolution will not be uniform within the footprint and due to this; there will be a trade off between resolution and coverage.
Figure 2. Illustration showing a multi beam sonar installed
tilted in a frame.
To cover a circle with radius 1.8 km with eight sonars, the footprint under the ice must be at least 1.4 km long for the extreme ice drift events (Figure 1).
Table 1 shows the required length of the footprint for some other possible combinations of ice drift speeds and number of instruments. The requirements with respect to width of the footprints are however, less strict. If sonar scans are available every minute, ice drifting with speed 1 m/s will move maximum 60 m between each scan. This means that a footprint width of 60 m is sufficient to capture all ice features passing the sonar.
29
2 Copyright © 2009 by ASME
to exceed the design criteria. Icebreakers or iceberg towing
to exceed the design criteria. Icebreakers or iceberg towing
In document
Ice Management in Arctic Offshore Operations and Field Developments
(Page 34-44)