ROVworld Subsea Information

Hectic final stage for marine activities
Date: Thursday, March 08, 2007 @ 08:00:00 EST

Hectic final stage for marine activitiesPrior to the Ormen Lange field commencing production in October, a hectic final stage of the first phase of the Ormen Lange development awaits, with extensive marine activities. Almost 1,100 vessel days will be worked before the field comes on stream.

The biggest tasks will be carried out by the vessels Nordnes, Tertnes, Geobay, Geofjord, and Skandi Neptune, in addition to eight guard vessels.

"The marine assignments in 2007 represent the final phase of an extremely extensive maritime operation, which reached its peak in 2006, with 2,500 vessel days. We are very pleased with the marine activities that have been carried out so far, and we have good control over the work that remains, where we are continuing to prioritize issues relating to health, safety and environment," Trond Eklund says. He is responsible for the remaining marine operations for the Ormen Lange development.

  Skandi Neptune  
  CONTROL CABLE: Subsea 7's multi-purpose offshore support vessel "Skandi Neptune" will lay the second control cable between Nyhamna and the Ormen Lange field this year. The first cable was laid in 2006. (Photo: Lillian Aasheim).  

Drilling and installation of Christmas trees

In addition to the major marine operations to be carried out in 2007, production wells will also be drilled, and wellheads (also known as Christmas trees) installed. This work will continue for the entire year, from the drillship West Navigator.

In total, 14 Christmas trees will be installed at a sea depth of 850 metres, with the help of West Navigator. Ten of the Christmas trees must be installed by the time production starts in October.

The Christmas trees will be delivered by FMC Kongsberg Subsea, and have a weight of 65 tonnes. With dimensions of 4 metres in width, 4.5 metres in length and 3.9 metres in height, the Christmas trees are the largest of their kind in the world.

By October, ten of the Christmas trees will be installed on the two templates that form part of the field's subsea production system.

Control cable number two

At the end of April, Subsea 7's multi-purpose offshore support vessel Skandi Neptune will start spooling the second control cable between the land-based facility at Nyhamna and the installations on the Ormen Lange field. The first cable was laid in the summer of 2006 using the same vessel.

Laying of the 123-kilometre long control cable - to be used for remote control of the installations on the field - is scheduled to start on 19 May, and will continue for around three weeks. The cable has been manufactured by Nexans in Halden, and is to be laid in a single length, which is coiled on a carousel with a diameter of 24 metres.

  West Navigator   Tertnes  
  DRILLING: The "West Navigator" drill ship will be used for the drilling of production wells as well as the installation of wellheads (also known as Christmas trees).   STONE DUMPING: The flexible fallpipe vessels "Tertnes" and "Nordnes" from Van Oord are filling the Ormen Lange pipeline and cable routes with stone mass and crushed stone.  

Stone dumping

Ever since 2004, the flexible fallpipe vessels Tertnes and Nordnes from Van Oord have been used for filling the route for the Ormen Lange pipelines and cables with stone mass and crushed stone.

Stones are used both as foundational support for the pipelines, to fill areas where the sea bed is particularly uneven, and as a protective layer on top of pipelines and cables.

Altogether, 3.6 million tonnes of stone will be dumped on the sea floor. Of this, 290,000 tonnes of stone remain to be deposited this year, and will be used as protection for the control cable that is to be attached to template B on the field.

The stone-filling work is due to be finished in November.

Digging work

Once the control cable has been laid, it must be buried at a depth of up to 2 metres below the sea floor. This work starts at the beginning of June, using the supply vessel Geofjord.

The digging of trenches for control cables and pipelines will be carried out using the remote-controlled Capjet machine, developed by Nexans. Capjet uses waterjet technology to "plow" a trench after the cables or pipelines have been laid. Fluidizing of the materials in the trench means that the pipeline sinks down, while at the same time the fluidized materials fall back into the trench, burying the cable naturally.

The digging work for 2007 covers a stretch of around 80 kilometres.

  Nexans CapJet "Spider"   Geofjord  
  Nexans CapJet "Spider".   GEOFJORD: The digging of trenches for control cables and pipelines will be carried out using the "Capjet" machine, which will be remote-controlled from the supply vessel "Geofjord".  

Mapping and surveying

During the digging and covering work, the multi-purpose offshore vessel Geobay will be used for mapping the sea-bed, as well as surveying and positioning. The mapping provides thorough documentation of the installation that is being carried out.

During the marine operations, transponders (acoustic transmitters) are used, in order to achieve sufficient accuracy of positioning in the most difficult areas. The transponders are removed again following use.

The work to map the sea bed and set out the transponders will start in March, and continue until November. During the last part of this process, the supply vessel Geofjord will be used.

Guard vessels will also be used throughout the year. In total eight such vessels will be used in the final stage of the marine activities.


This article comes from ROVworld Subsea Information

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