Subsea Positioning - ccop.or.th

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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


• Sound velocity analysis (Transmission Loss)

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LBL Operations


– Viewshed analysis (ArcGis)

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LBL Operations

• Planning – Coverage analysis (cont)

– Viewshed 2m

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LBL Operations


– Viewshed 5m

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LBL Operations


– Viewshed 10m

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LBL Operations


– Viewshed 15m

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LBL Operations


– 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


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Project Experience


– 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

150

200

250

300

350

400

450

500

550

600

650

700

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


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


– 4 sub network designed

– Total number of 43 transponders

deployed and calibrated.

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Project Experience


– 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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Subsea Positioning - ccop.or.th

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