Paving the way through glacial boulders

Meg Chesshyre
Wednesday, August 1, 2012

As the giant Nord Stream project, involving 3 million tonnes of rock dumping over two and a half years, comes to an end, Tideway has picked up another substantial project from Subsea 7 for Total's Laggan Tormore project. Meg Chesshyre reports.

Subsea 7 has a contract to install among other things an 8in monoethylene glycol (MEG) and 2in service pipeline and control umbilicals for the Laggan Tormore project West of Shetland. This is a very interesting project, which takes a lot of our capacity, explains Tideway director Hugo Bouvy. The pipeline route crosses a glacial boulder field, with big boulders several metres across on a clay foundation. Post trenching of the pipelines and umbilicals cannot be undertaken through the boulder fields. We have therefore covered the boulder fields with a blanket of rock. Subsea 7 is in the process of laying the pipelines over these rock blankets using the reel ship Seven Oceans and the support vessel Normand Oceanic. Tideway will then return and cover everything post-lay.

The quantities of rock required are again huge. Around 400,000te of rock has been positioned prior to pipelay, and 1.5 million tonnes are expected to be required in total. The rock dumping work will continue through the winter of 2012. All three Tideway fallpipe vessels Flintstone, Seahorse and Rollingstone have already been used on the first part of the project and are expected to return for spells of the post-lay period.

Bringing the bulk carriers to our vessels is the only way possible to execute the [Laggan Tormore] work within the required schedule. Hugo Bouvy

Because of the huge capacity required, and in order to meet Subsea 7's tight schedule, Tideway has adopted a completely different approach to the project. Normally the vessels combine fetching the rock with taking it to the field. In this instance Tideway has hired bulk carriers from Stema to collect the rock from Norway. The bulk carriers are moored at the quayside in Sullom Voe, and the rock is loaded onto the Tideway vessels, where it is redistributed by the vessels own cranes. Loading takes about 12 hours.

Tideway's Flintstone loading rock bound for West of Shetland from a Stema bulk carrier.

By doing this we take about three days sailing out of the production cycle and we can increase production enormously, notes Bouvy. Of course, this is also costing a lot of money, but we are creating more capacity, bringing the bulk carriers to our vessels. It is the only way possible to execute the work within the required schedule.

Tideway is also carrying out rock dumping for pipelay contractor Allseas, which is laying the twin 141km, 18in import pipelines from the Laggan Tormore fields to Sullom Voe.

Under a frame agreement with Statoil, a JV of Tideway and Boskalis was recently awarded a series of rockdumping assignments offshore Norway, including amongst others the Asgard, Skuld, Hyme and Visund projects. A total of about 1 million tonnes of rock will be required. The contract started in June, and will run until the end of the year.

Bouvy notes that Australia is becoming increasingly important for everybody. Tideway has just been awarded the secondary stabilization works for the Chevron's Wheatstone pipeline, which is being laid by Allseas. The pipeline will be pre-trenched for the first 50km, from the landfall to a water depth of 50m, then covered with sand and rock afterwards to protect it from cyclones. Meanwhile, parent company DEME has already been awarded a €916 million EPC contract by Bechtel

for the dredging works associated with Wheatstone. DEME is also currently executing a large-scale dredging project in Gladstone for the Western Basin LNG development.

Bouvy believes that in two years from now the DEME group will be employing as many as 1000 people in Australia.

Australia poses particular challenges because of its stringent environmental and health and safety standards. Vessels need to be Australianised to ensure they aren't carrying any non-indigenous species. Special dredging methods and monitoring are required to protect coral. Tideway is well placed here, having had previous experience of working in Australia for Woodside on the Pluto project.

Another interesting area for Tideway is the marine renewables business where the accuracy of placement is very important. A few years ago the company developed a patented Offshore Leveling Tool (OLT), which makes it possible to smooth out the rock carpet in a very accurate manner. Tideway uses its inclined fallpipe system, a patented system first used by the company on the Deep Panuke project offshore Canada (OE September 2011). The inclined fallpipe makes it possible to provide scour protection at the foot of the structures without damaging the coating, anodes or J-tubes. According to Bouvy, CAR (construction all risks) insurances will no longer provide cover for rock placement, unless the inclined fallpipe method is used.

Recent renewables projects have included Walney and Gwynt-y-Mor wind farms in the Irish Sea and Riffgat in the German Bight. Next year Tideway will start work on the Northwind wind farm project offshore Belgium.

An area of increasing importance for Tideway is power cable installation. The company started off laying the NorNed power cable between Norway and the Netherlands (OE September 2005), then installed all the cables at Thornton Bank. It has now been awarded the infield cables for the Northwind project. Cable lay is currently carried out by the Pompei, but Tideway has completed the necessary engineering for converting the Rollingstone into a cable laying vessel, if the market requires it.

Hugo Bouvy believes that the biggest challenge facing his company and others in an increasingly global industry is finding enough skilled people in their home markets to handle the workload. The people working for us become more and more international, from Canada, India, Mexico, Portugal, Spain, Italy. The difficulty is finding people prepared to work abroad, he says. OE

Categories: Subsea Pipelines Vessels Europe Installation Engineering

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