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INTRODUCTIONPRINCIPLES, METHODS AND TOOLSSITE SURVEY OPERATIONSRECENT DEVELOPMENTS -AUV SURVEY OPERATIONS

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Just about anything you need to put on or in the seabed; examples:– Exploration Surveys– Rig Site Surveys– Platform Site Surveys– Pipeline Route Surveys– Cable Route Surveys– Field Development Surveys– Clearance, Abandonment and

Inspection Surveys– Wind Farm Surveys

What do you need site surveys for?

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EXAMPLES OF SITE SURVEY REQUIREMENTS

WIND FARMS

SEMI-SUBMERSIBLE DRILLING RIGS PLATFORMS

PIPELINE ROUTES

SUB-SEA PRODUCTION

FACILITIES

ANYTHING THAT GOES ON OR IN THE SEABED…

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What are we trying to find out?– Water depths, seabed relief,

seabed gradients– Obstructions, debris, wrecks,

existing installations– Seabed sediment types– Shallow geology, foundation

design, trenching conditions– Geohazards such as shallow gas

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What if you don’t do a site survey?...

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NORTH SEA SHALLOW GAS BLOWOUT

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OFFSHORE EGYPT GAS BLOWOUT 2004

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PRINCIPLES, METHODS AND TOOLS

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BASIC PRINCIPLES

Use of geophysical ‘remote sensing’techniques, calibrated by some limited

‘ground truth’ sampling.Virtually always use acoustic methods

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Water depth measurement, seabed topography: >ECHO SOUNDERSingle BeamMulti Beam

Detection/identification of seabed obstructions: >SIDE SCAN SONARInterpretation of soil lithology, shallow gas detection: >SHALLOW SEISMIC

ACOUSTIC METHODS

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Echo Sounding

Single beam

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ECHO SOUNDERS

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100m

Multi-beam echosounder: Topographic Image

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SHADED RELIEF FROM MULTIBEAM ECHO SOUNDER

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ROUTE VISUALISATION FROM MULTIBEAM ECHO SOUNDER

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SIDE SCAN SONAR

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Seismic Systems: Principles

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PingersBoomersMini-airgunsCHIRPSparkers

SINGLE CHANNEL SEISMIC METHODS

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SINGLE CHANNEL METHODS

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SINGLE CHANNEL METHODS – Chirp profiler

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SINGLE CHANNEL METHODS – Chirp profiler

20 m

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SINGLE CHANNEL METHODS – mini-airgun

30 m

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MULTI CHANNEL METHODS

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HIGH-RESOLUTION 2D SEISMIC VESSEL

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3D SEISMIC – MAINLY USED FOR EXPLORATION

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3D SEISMIC – A lot of sensors to be positioned accurately

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3D Seismic Survey – result is a seismic “cube”

1000 m

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• Grab Samplers

• Gravity Corers

• Vibrocorers

• Cone Penetrometers

• Boreholes

GEOTECHNICAL SAMPLING

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Environmental SurveysJNCC guidelines necessitate environmental surveys in sensitive areas

• Pockmark fields – active venting encourages marine life growth and reef development

• Sabellaria – tube worms• Herring spawning grounds• “Reefs”

Seabed photos & sediment grab samples taken as part of geophysical surveyEIA becoming standard part of site surveysGeophysicists working with marine biologists

Sabellaria spinulosa

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INTERPRETATION AND PRESENTATION

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SEABED FEATURES CHART

Distribution of seabed sedimentsTopographic features (sands waves etc)Rock outcropsPockmarksExisting infrastructure; pipelines, cables etcWrecksItems of debrisSeabed Features Chart should comprise interpretation of Echo Sounder, magnetometer and side scan sonar data with seabed samples

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SHALLOW SOILS CHART

Map of depth to significant sediment interfaceIdentify soil profile in the required depth zoneLocate potential obstructions; boulders, gravel layers etcIdentify potential unconsolidated soils / loose sands – geotechnical weak units

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FOR PIPELINE ROUTES - ALIGNMENT SHEET FORMAT

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3D perspective

Shaded relief

Colour coded seabed gradient

SEABED VISUALISATION

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Seabed Features/Hazards map – Use GIS

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SITE SURVEYOPERATIONS

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• Construction of Survey Programme

• Positioning of Vessel

• Positioning of Sensors

• Quality Control of Bathymetry data

THE SURVEYORS ROLE

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SURVEY LINE PLAN FOR JACK-UP RIG

Distances in metres1 km

Plus tie line to adjacent borehole or survey area

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SURVEY LINE PLAN FOR SEMI-SUBMERSIBLE RIG

Distances in metres1 km

Plus tie line to adjacent core location or site survey

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AUV SURVEYS

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THE DEEP WATER SOLUTION

Traditional survey methods have numerous drawbacks to the acquisition of geophysical data in Deep Water areas.For deep water areas better resolution and better positioning is neededThe survey industry’s solution:

The Autonomous Underwater Vehicle (AUV)

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AUV OPERATIONS

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Fugro’s “Echo Surveyor” AUV

• Kongsberg HUGIN 3000.

• Semi-autonomous vehicle independently powered and controlled (cable free).

• Depth rated to 3000 metres.

• Aided Inertial Navigation System provides extremely accurate positioning.

• Positional accuracy of the AUV is less than 5 metres, significantly better than towed systems.

AUV OPERATIONS

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AUV DATA QUALITY

Bathymetry from 3D seismic data

AUV mounted multibeam echo sounder data

Improved bathymetry data

quality... …compared to

3D seismic

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AUV DATA QUALITYImproved sub-bottom profiler data quality...

2DHR Data AUV Chirp Data

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INTEGRATED INTERPRETATION STRATEGY

Bring together all data types and background information together on one platform – SMT Kingdom Suite

SMT

Multi-layer Sonar Mosaics

Shaded Relief Bathymetry

Chirp

2DHR / 3D

Contoured Bathymetry

Cultural Data

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INTEGRATED INTERPRETATION STRATEGY

Many features can only be properly characterised by the use of several different data types

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REPORT DELIVERY

Seabed FeaturesSMT

Interpretation Products

Shallow Soils

Shallow Geohazards

•hardcopy•PDF•CAD•GIS

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Thank You

geophysical site survey geophysical site survey

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