Jaime Kammerzell - Special Correspondent
The 2009 survey of offshore pipelay vessels byOffshore magazine is expanded to include vessels working worldwide, which opened the door for eight new companies to join in the survey. Other notable differences from the previous survey in 2004 include company mergers and name changes.
Ascot Constructors Offshore joins the survey with two pipelay barges. In February 2007, Ascot acquired the Nigerian assets of Willbros Group Inc., an international contractor that provides construction and engineering services to the oil and gas and power industries. The company is based in West Africa.
Boskalis Offshore also adds two vessels to the survey; one a trailing suction hopper dredger and the other a fallpipe vessel. Its parent company, Royal Boskalis Westminster N.V., is a global services provider operating in the dredging, maritime infrastructure, and maritime services sectors. The company holds a fleet of over 300 vessels.
China National Offshore Oil Co. adds four vessels to the survey, including one newbuild. The company primarily works in Bohai Bay off China, which is its most important and largest oil and gas production base.
Emas Offshore Construction owns and operates FPSOs and provides offshore construction services. The company, based in Asia, has added one pipelay barge to the 2009 survey.
Likewise, International Offshore Services LLC, formally International Boat Rentals Inc., adds one vessel to the survey. The company’s International Construction Group LLC provides heavy lift, platform and marine salvage, and pipeline installations using its Zap-Lok Pipeline Technology System, and well intervention capabilities to companies operating in the GoM.
NorCE Offshore adds one derrick lay barge to the 2009 survey. NorCE is an offshore construction and installation company based in Singapore. The company primarily operates in the Asia-Pacific region.
Sea Trucks has the second largest fleet of pipelay vessels new to our survey with five DP lay/crane/accommodation vessels. The West Africa-based company offers services worldwide.
Swiber has the largest fleet of pipelay vessels new to the 2009 survey. The Singapore-based company has seven vessels working offshore Asia, and serves the region with offices in Southeast Asia, India, and Africa.
Another change to the survey is Stolt Offshore’s disappearance. This is in name only, as Stolt Offshore changed names to Acergy in 2006. Acergy kicks off the survey with nine pipelay vessels.
Global Industries leads the survey with 21 pipelay vessels. The company has 11 derrick/lay barges, four derrick barges, four multi-service vessels, and two lay/bury barges. Saipem follows with 17 vessels. One diving support vessel is under construction and not yet named. Completion is expected in 3Q 2011.
Installation methods
Today’s pipelay vessels still work in shallow waters, but often are asked to lay pipe in remote areas and in water depths greater than 3,000 ft (914 m). To be commercially viable, most vessels lay multiple operational lines. These lines are either welded together on the pipelay vessel as it is laid on the seafloor, or the entire pipe length is joined together on land and transported to the offshore location for installation. Dynamic positioning onboard these vessels help battle various stresses, such as loop currents or eddies, greater span distances, and uneven seafloor topography.
There are three main pipelay methods: Tow-in, S-lay, and J-lay.
The Tow-in method suspends the pipe in the water in one of four ways: surface tow, mid-depth tow, off-bottom tow, and bottom tow.
- Surface tow: A tug boat tows the pipe on top of the water, and buoyancy modules help to keep it on the water’s surface.
- Mid-depth tow: Buoyancy modules work with the propulsion of the tugboat to keep the pipeline submerged until it is in place. Then it settles to the seafloor.
- Off-bottom tow: Buoyancy modules and chains (weights) work against each other to keep the pipe just above the seabed until it is in place. The buoys then are removed and the pipe settles to the seafloor.
- Bottom tow: No buoyancy modules are used. The pipe is dragged on the seafloor until in place. This is used only in shallow water.
S-lay is named for the way the pipe curves as it is installed. The pipe gently falls off the stern of the vessel and curves down onto the ocean floor, forming the shape of an “S” in the water. As many as 4 mi/d (6 km/d) of pipe can be installed using the S-lay method in up to 6,500 ft (1,981 m) of water.
Similar to S-lay, the J-lay pipeline installation takes the shape of a “J” underwater. The pipe only curves once because it is lifted using a tall tower on the vessel and enters the water almost vertically. This puts less stress on the pipeline, which allows the J-lay method to work in deeper waters.
View the pipelay vessels poster online atwww.offshore-mag.com/index/maps-posters.html.
The number of deep, remote oil and gas field discoveries increases every year, often yielding record deposits. Consequently, the need of subsea pipelines to transport the oil and gas has increased. According to Infield Systems’Global Perspectives Pipelines & Control Lines Update Report 2009/13, the total pipelines and control lines capital expenditure is forecast to exceed $265 billion over the five-year period. This equates to 103,435 km (64,272 mi) of lines being installed, of which 81,293 km (50,513 mi) will be pipelines and 22,142 km (13,758 mi) will be control lines, according to the report. Combined, these represent an increase of 68% in installations over the previous five years, according to the report.
