Workshop on seabed habitats of environmental concern Jørn Spiten
Content Pipeline - route design Seabed Intervention - Trenching - Ploughing - Dredging - Rock installation 2
Pipeline routes 3
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 Minimise disadvantages for 3rd parties - fishing areas - other licences, future wells/platforms - distance to parallel pipelines Environmental aspects - coral reeves - threatened specimens - oil spill Avoid/minimise risks/hazards - geohazards - sand waves - environmental forces - ship lanes, anchoring, wrecks - dropped objects 4
Ormen Lange case - slide area N TO SHORE TOP OF SLIDE EDGE WATER DEPTH = 250 m DEVELOPMENT AREA WATER DEPTH = 850 m Survey coverage of the slide area Slide 5 10 KM
Long free spans Slide 6
Advanced routing KP 8 KP 9 KP 10 KP 11 KP 12 Slide 7
Seabed intervention 2011-11-13
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
Jet trenching 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 Slide 10
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
Plough dimensions Slide 12
Ploughing trial Slide 13
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
Dredging Slide 15
Rock dumping Used for several purposes: - protection - upheaval resistance - free span limitation - sectioning - crossings - stabilisation - supports 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) Slide 16
Rock dumping Rock dumped through fall pipe Fall pipe end position controlled by ROV Slide 17
Safeguarding life, property and the environment www.dnv.com 18