Transcript
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Subsea Positioning In deep water
PETRONAS - PETRAD - INTSOK – CCOP
DEEPWATER SUBSEA TIE-BACK
Damai Puri Resort & Spa, Kuching, Sarawak, MALAYSIA
24TH - 26TH January, 2011
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Supplier to the oil & gas industry
Providing survey and positioning services
Experienced offshore surveyors
High quality and proven technical solutions
Supporting projects worldwide
Offices in Singapore and Norway
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Rig and FPSO
Operations
Marine construction
work
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Experienced project
managers and
offshore staff
Multi beam services
for As-Laid
Pipe and cable survey
Complete solutions
for subsea
positioning support
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Contents
• Subsea Positioning methods
– Ultra Short Base Line (USBL) Systems
– Long Base Line (LBL)
– Inertial Navigation Systems (INS)
• LBL operations
– Planning
– Deployment and calibration
– Operations
• Project Experience
– Ormen Lange Field development, Norway
– MA D6 Field development, India
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Subsea Positioning methods
• Most systems are based on acoustic or a combination
with acoustic.
• Two main principles used:
USBL
Range, angle and bearing
from a fixed transducer (on a
vessel or rig) to a
transponder.
LBL
Range from fixed
transponders (on the
seabed) to a Transducer
or Transponder
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USBL
• Accuracy:
– Typical 0.2-0.5% of slant range.
• Advantages:
– Most Construction vessels, Rigs (semi) and many anchor
Handling Tugs have USBL systems installed.
– No time consuming deployment or calibration of seabed
transponders.
• Disadvantages:
– Accuracy in deep water
– Update rate in deep water
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LBL
• Accuracy:
– Typical better than 0.1m relative accuracy (depth independent)
• Advantages:
– Accuracy in deep water
– Update rate in deep water (from ROV)
– Fixed reference for all users
• Disadvantages:
– Time consuming to deploy and calibrate
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INS
• Acoustic and Inertial positioning principles in combination is ideal,
since they have complementary qualities. Acoustic positioning is
characterised by relatively high and evenly distributed noise and
no drift in the position, whilst inertial positioning has very low
short-term noise and relatively large drift in the position over time.
• Accuracy:
– Dependent on guiding sensor (USBL/LBL, DVL. IMU)
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LBL Operations
• Planning
Experience with LBL and subsea positioning operations over
years have shown that the planning phase is essential in saving
time and cost during the offshore phase.
iSURVEY has over the years developed a systematical approach
to the planning of LBL networks. The planning consists of the
following phases:
– Identification of requirements • Abosulte/Relative positioning accuracy requirements
• Attitude requirements
• Coverage requirements
• Update rate requirements
• Instrumentation on structures
– Detailed network planning
• Coverage analysis
• Accuracy analysis
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LBL Operations
• Planning – Coverage analysis
The basis for the coverage analysis is to ensure that the planned transponder
locations has both the sufficient coverage for the calibration operations and for
the tracking operations
Bakground information on the enviromental condition (sound velocity profile),
Noise level on ROV and/or vessel is used to calculate expected range
limitation.
iSURVEY are using ArcGIS for the coverage analysis. Based on a Digital
Terrain Model of the seabed (and structures), transponder and stand data
(height above the seabed), a visual coverage map is produced.
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LBL Operations
• Planning – Coverage analysis (connt)
• Sound velocity analysis (Raytrace)
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LBL Operations
• Planning – Coverage analysis (connt)
• Sound velocity analysis (Transmission Loss)
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LBL Operations
• Planning – Coverage analysis (connt)
– Viewshed analysis (ArcGis)
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LBL Operations
• Planning – Coverage analysis (cont)
– Viewshed 2m
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LBL Operations
• Planning – Coverage analysis (cont)
– Viewshed 5m
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LBL Operations
• Planning – Coverage analysis (cont)
– Viewshed 10m
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LBL Operations
• Planning – Coverage analysis (cont)
– Viewshed 15m
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LBL Operations
• Planning – Coverage analysis (cont)
– Multiviewshed (for tracking)
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LBL Operations
• Planning – Accuracy analysis
• The accuracy analysis is performed with the survey adjustment software
MOVE3.
• Based on experience, uncertainty figures are used in the calculations to give as
close to real life results as possible.
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LBL Operations
• Planning – Accuracy analysis
• The accuracy analysis is performed with the survey adjustment software
MOVE3.
• Based on experience, uncertainty figures are used in the calculations to give as
close to real life results as possible.
• Expected accuracy both for calibration and tracking are calculated
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LBL Operations
• Deployment and Calibration – Transponder stands
• Several types can be supplied, depending on requirments
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LBL Operations
• Deployment and Calibration
– Calibration
• Based on the planning data, a minimum of baseline measurements, Box
In etc. can be performed → Saving vessel time
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LBL Operations
• Operations
To optimise offshore operations:
– Detailed SOW for both the deployment and calibration are prepared, (the
level of details down to specifying each baseline that should be measured).
The SOW also included guidelines.
– Processing and adjustments done onshore, only data collection offshore.
– QC of data both onshore and offshore
– Detailed background data made available for the offshore vessel. All the data;
DTM, routes, proposed transponder locations, view sheds, error ellipses etc.
was collected in ArcGis and exported to the free ArcReader format.
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Project Experience
• Ormen Lange Field Development
– iSURVEY AS was contracted by Statoil to do the planning of the LBL networks
at the Ormen Lange field development 2005-2009.
– iSURVEY AS also supported the offshore operations with personnel to support
the installation and operations of the LBL networks during the installation
activities during the same period.
More than 200 transponders deployed and calibrated
More than 30 LBL networks
Water depth 240-850m
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Project Experience
• Ormen Lange Field Development
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Project Experience
• Ormen Lange Field Development
– Experience showed that focus should be on the following issues:
– Sound velocity control and modelling
– Terrain (visibility)
– Noise level (on vessel and ROV’s)
– Operator experience level
– Strengthening planning
Sound Velocity Profiles E03 area
0
50
100
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1455 1460 1465 1470 1475 1480 1485 1490 1495 1500 1505
Sound Velocity (m/s)P
ressu
re
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Project Experience
• MA D6 Field Development
The Krishna Godavari MA-D6 field
development is based on production to a
turret-moored floating production, storage
and offloading vessel (FPSO) from the
subsea production systems. These
components are interconnected through a
combination of umbilicals, risers and
flowlines. The field is located in a water
depth of between 1100m and 1400m and
approximately 60 km offshore of
Kakinada on the east coast of India
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Project Experience
• MA D6 Field Development
The survey scope of work to be undertaken
includes the following tasks:
- Dimensional control of suction anchors and manifold
structure
- Installation and calibration of Survey Positioning
System Check stations
- Mobilisation of survey and positioning equipment
- Alongside calibrations and wet testing of equipment
- Deep water wet tests during transit to field
- Survey and positioning system calibrations on field
arrival
- LBL array installation and calibrations
- Installation of marker buoy(s) for structure
deployment
- Pre-installation survey of mooring line corridors,
suction anchor locations and manifold structure
location
- Installation support and monitoring during operations
- Vessel and ROV positioning
- As Built Surveys
- Recovery of LBL arrays
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Project Experience
• MA D6 Field Development
– 4 sub network designed
– Total number of 43 transponders
deployed and calibrated.
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Project Experience
• MA D6 Field Development
– Extensive planning saved offshore time
– Experienced operators offshore that can do
the required operational adjustments
– Onshore processing, less workload on
offshore personnel. (Processing done
onshore in Norway)
– Logistic and spare part needs consideration
and detailed planning when operating in
certain regions.
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Subsea Positioning in Deep Water
Thank you !
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