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Hydrographic Survey, pipelay and other offshore survey activities

Hydrographic Survey - Offshore engineering and construction

For more about hydrographic survey operation click here. For pictures of platforms and other offshore installations click here. An example of part of the development of one field, Tyrihans, click here.

In addition to performing surveys and seabed investigations offshore survey (or more correctly ROV support) vessels perform a wide variety of construction and engineering related tasks. Some examples of these activities can be found on this page.

Dive support vessel CSO Wellservicer
CSO Wellservicer at CCB offshore base outside Bergen

Often other vessels are invloved, whether it be anchor handlers, supply vessels or DSVs (Diving Support Vessels). Often special tooling must be mounted on the ROV in order to perform such tasks.  Some recent developments such as Snøhvit and Ormen Lange have no surface platforms in place, with all structures based subseas. These structures are operated either from shore or by support vessels equipped with ROVs.

Draugen Loading Buoy
The Draugen Loading buoy is used by tankers to fill up with cargo, to do this they must connect to a hose. The rigging on this hose required repair so our task on this occasion was to use the ROV to hook up a wire so the supply vessel "Ocean Sky" could pull the hose up and make repairs to the rigging.

Amazingly a Long-tailed Duck continued to feed around the leg of the loading buoy - apparently unconcerned by the activities of two vessels working in close proximity to it.

Supply vessel Ocean Sky at Draugen Loading buoy
Supply vessel "Ocean Sky" pulling the hose from the loading buoy on deck

Langeled RFO work at Sleipner

As part of the preparations for the supply of gas to the UK from the Ormen Lange field via the so-called Langeled pipeline various "pigging" and flooding work had to be done. Here our vessel worked in conjunction with the DSV Acergy Osprey - a Dive Support vessel I worked on briefly in the 1990s.

Here the Acergy Osprey is seen working beside the Sleipner platform.

DSV Acergy Osprey DSV Acergy Osprey at Sleipner platform
DSV Acergy Osprey at  Sleipner, February 2007
DSV Acergy Osprey at Sleipner, February 2007

Mattress about to be deployed
Concrete mattresses are often used to protect subsea installations, especially pipelines.

Dawn over the Acergy Piper
Dawn (03:30!!) over the Acergy Piper, Tyrihans, June 2007

There are various types of pipelay vessel - some operate in "DP" using thrusters and propellors to keep themselves in position. Others use anchors - and during such a pipelay there can be an amazing number of vessels involved. The barge itself, anchor handling vessels, pipe carriers (to re-supply the barge) and lay support vessels.

The business end of the Acergy Piper

Counteracts such as depicted above are used to physically constrain the position of the pipeline during the lay. They are usually recovered after use.

Pipelay Initiation

Initiation piles are used to anchor the pipeline when commencing a pipelay. These piles need to be driven into the seabed. Below is a picture of a piling hammer being recovered on completion of such an operation.

Piling hammer being recovered to deck

Botnica, Baltic ice breaker in winter, construction in summer
Construction Vessel / Ice-breaker Botnica

Construction vessel S7000 near Stavanger
Construction vessel S7000 near Stavanger, spring 2010

Construction vessel S7000 near Stavanger

Construction vessel S7000 at Valhall
Construction vessel S7000 at Valhall, summer 2010

After a pipeline is laid and before it is hooked up and put into production it must be checked and tested. This will often mean that the pipeline is flooded, "pigged" and pressured up. "Pigs" are run through the pipeline to perform various checks before pressure testing to ensure there are no leaks. This task will be performed using an offshore support vessel and requires a fair bit of deck space.

Bleeding off a pipeline after a pressure test
Bleeding off a pipeline after pressure testing. 

Rock Dumping (or Rock installation)
An integral part of many offshore construction operations is rock dumping, Rocks, gravel and sand is used for various reasons both prior to and following the installation of structures such as templates or pipelines. Rock berms can provide a stable and level surface on which to deploy something, support a pipeline where it would otherwise be in freespan or provide protection from other activities such as trawling.

FFPV Tertnes
The FFPV (Flexible Fall Pipe Vessel) Tertnes is one of a number of rock dumping vessels.

Rock dumping vessel Simon Stevin
Rock dumping vessel Simon Stevin working off Kollsnes, Øygarden

Dredging and trenching
Sometimes it is necessary to uncover structures or pipelines buried under rock dumps, or it may be necessary to dig a trench. There are many ways of doing this but one of the more ingenious is pictured below. Operators use a virtual seabed to dig in so a DTM of the area is a prerequisite for this kind of work - often updated at regular intervals as work progresses.

On deck

Skanmaskin being launched

Launching the digger

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