Pipelines and seabed intervention

Jørn Spiten

18 October 2013

Pipelines and seabed intervention

Workshop on seabed habitats of environmental concern

© Det Norske Veritas AS. All rights reserved.


18 October 2013

Content

Pipeline

- route design

Seabed Intervention

- Trenching

- Ploughing

- Dredging

- Rock installation

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Pipeline routes

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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

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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



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Slide 6

Long free spans



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Slide 7

Advanced routing

KP 12

KP 11

KP 8

KP 9

KP 10



2011-11-13

Seabed intervention



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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



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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

http://www.youtube.com/watch?v=yiu12lpnmKM



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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



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Plough dimensions

Slide 12



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Ploughing trial

Slide 13



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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



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Dredging

Slide 15



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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)



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Rock dumping

Rock dumped through fall pipe

Fall pipe end position controlled

by ROV

Slide 17



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Safeguarding life, property

and the environment

www.dnv.com

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Documents

Pipelines and seabed intervention