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Jørn Spiten
18 October 2013
Pipelines and seabed intervention
Workshop on seabed habitats of environmental concern
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Content
Pipeline
- route design
Seabed Intervention
- Trenching
- Ploughing
- Dredging
- Rock installation
2
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Pipeline routes
3
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Pipeline Routing - General
Minimise route length
- Installation aspects
- minimum curvature
- start/end, shore approach, tie-in
- laying tolerances/corridor
Minimise seabed intervention costs
- free span intervention
- rock outcrop, boulders
- trenching/burial
Avoid/minimise risks/hazards
- geohazards
- sand waves
- environmental forces
- ship lanes, anchoring, wrecks
- dropped objects
Minimise disadvantages for 3rd parties
- fishing areas
- other licences, future wells/platforms
- distance to parallel pipelines
Environmental aspects
- coral reeves
- threatened specimens
- oil spill
4
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Slide 5
DEVELOPMENT
AREA WATER DEPTH = 850 m
TOP OF SLIDE EDGE WATER DEPTH = 250 m
10 KM
N
TO SHORE
Survey coverage of the slide area
Ormen Lange case - slide area
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Slide 6
Long free spans
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Slide 7
Advanced routing
KP 12
KP 11
KP 8
KP 9
KP 10
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
2011-11-13
Seabed intervention
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Main methods
Commonly used
- Jet trenching – post-lay
- Ploughing – pre- and post-lay
- Dredging – pre- and post-lay
- Rock dumping - pre- and post-lay
Occasionally used
- Mechanical excavator – post-lay
- Remotely operated grab-dredger – pre-lay
- Sand/cement bags – post-lay
- Other mechanical supports
- Directional drilling
Slide 9
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Jet trenching
Slide 10
System that employs water jets to cut or
liquefy the soils around and in front of a
pipeline.
Soils removed by air lifts, water ejectors or
submersible pumps.
Used post-lay
Typical for cables, umbilicals and small
diameter pipelines
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Ploughing
Basically giant version of the agriculture plough
Pulled along the pipeline route and opens a wide trench
Both before and after pipe laying
Post-lay ploughing is steered by the pipeline
May use a backfilling plough or share
Different ploughs for different soil conditions
Multi-pass to get deeper
Large, heavy equipment – may damage pipeline in case of malfunction
Ploughing is fast
Associated with relatively high mobilization costs.
Slide 11
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Plough dimensions
Slide 12
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Ploughing trial
Slide 13
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Dredging
Soil is grabbed and lifted away or
Soil is sucked into a hose
Transported away from the area
(through either blasting it out through a
pipe or through storage tanks onboard
the dredging vessel).
Typically used in very shallow waters
and in landfalls.
Used pre-lay
Slide 14
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Dredging
Slide 15
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Rock dumping
Used for several purposes:
- protection
- upheaval resistance
- free span limitation
- sectioning
- crossings
- stabilisation
- supports
Slide 16
Used pre- and post-lay
Used for pipelines in operation
Relatively fast and cheap method if
transport distance not too long
Cheap in North Sea
Disadvantages for fisheries (trawling)
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Rock dumping
Rock dumped through fall pipe
Fall pipe end position controlled
by ROV
Slide 17
© Det Norske Veritas AS. All rights reserved.
Pipelines and seabed intervention
18 October 2013
Safeguarding life, property
and the environment
www.dnv.com
18