Decommissioning activity was brisk in 2020, led by offshore infrastructure removals in the North Sea and offshore Nova Scotia
Operating in Morecambe Bay, just 24 km off of the coast of Blackpool, UK, the mammoth Pioneering Spirit, the world’s largest heavy-lift construction vessel, will be “an impressive sight” says Spirit Energy project manager Donald Martin.
“After two years of preparing the DP3 and DP4 installations for removal, we’re now looking forward to one of the most significant milestones in the project, with the removal of both platforms,” says Mr Martin.
In its first assignment outside of the North Sea, Pioneering Spirit will use its single-lift technology to remove two 11,000-tonne gas production platforms in the East Irish Sea. Mr Martin says the vessel’s single-lift methodology made it a good fit to safely execute the project.
Before those lifts can take place, Allseas must carefully plan and prepare the gas platforms for removal. Among the ongoing preparations are the cutting and removal of risers, caissons and conductors, cutting the platforms’ steel legs, strengthening the topsides and installing made-to-measure lift points. Additionally, the workscope involves extensive subsea activities – removal of mattresses, spools, cables and umbilicals – requiring more than 180 separate lifts by Allseas purpose-built construction support vessel (CSV) Oceanic.
Allseas spokesperson Jeroen Hagelstein says that while Covid-19 precautions will make the logistics of the project – moving equipment, supplies and personnel – more complex, it won’t hamper operations. Those same precautions were in place in 2020, and “we successfully executed three projects last year in the North Sea,” he said.
However, the operational conditions in the East Irish Sea will be challenging for the project.
Pioneering Spirit will have to contend with strong currents and shallow water – 22 m to 25 m deep – but the mammoth vessel’s unique hull shape, in combination with its active motion compensation system, should provide good wave response behaviour and a stable platform for the large lifts.
The platforms were once part of Spirit Energy’s complex of eight installations in Morecambe Bay. As the field matured, the DP3 and DP4 installations became unnecessary; gas reserves have now been tied into the larger, manned Central Morecambe platform nearby.
Spirit Energy says the 12 wells which were connected to the DP3 and DP4 platforms have already been plugged and abandoned – using a slant rig to accommodate the angle at which the wells were drilled in the 1980s to access the gas reservoir below the seabed – and the platforms will soon be safe to be lifted and taken back to shore.
The size and capabilities of Pioneering Spirit are often described in superlatives. Built over a three-year period at South Korea’s Daewoo Shipbuilding & Marine Engineering (DSME) and delivered in 2014, the twin-hulled vessel is 382 m long and 124 m wide. At the bow, a slot 122 m long and 59 m wide, enables Pioneering Spirit to move around a platform and lift and transport entire topsides using eight sets of horizontal lifting beams.
For jacket removal and installation, two 170 m long lifting beams, which can rotate on hinges, will be located at the vessel’s stern.
Complementing the lifting systems is a 5,000-tonne special purpose crane for additional lifts, such as lighter topsides and jackets, modules and bridges.
Pioneering Spirit will lift both the DP3 and DP4 platforms – well within its limits of lifting 48,000-tonne topsides. The infrastructure will then be transferred for recycling to the new facility operated by Cesscon Decom at Fife Energy Park in the UK.
In 2020, Pioneering Spirit spent the summer season in the North Sea completing three decommissioning campaigns, the last of which was a single-lift removal of the 14,200 t Ninian Northern topsides for CNR International (CNRI).
Located 160 km northeast of the Shetland Islands, the Ninian Northern platform comprised topsides modules for drilling, production and accommodation, all supported by an eight-legged jacket standing in 140 m water depth.
“Heerema removed more decommissioned offshore infrastructure than had ever been achieved by a single contractor in one year”
To prepare for the removal of the topside modules, those eight steel legs were cut in 2019. Once removed, the topsides were transported by Pioneering Spirit to the Peterson-Veolia yard in Dales Voe, Shetland, for disposal. However, Pioneering Spirit’s work at the field is not done. It will return to the North Sea in the summer season of 2022 to remove the Ninian Northern platform’s supporting jacket structure.
Prior to the Ninian Northern platform project, Pioneering Spirit completed the removal of the processing and accommodation topsides and flare jackets, as part of the Tyra Redevelopment Project for Total E&P Denmark. Pioneering Spirit removed more than 27,000 tonnes of platform facilities from the North Sea’s Tyra gas field, transporting the structures to specialist yards in Denmark and the Netherlands for recycling.
Allseas’ role in the redevelopment project covers engineering, preparation, removal, transportation, load-in to shore and recycling of the Tyra East Alpha (TEA) and Tyra West Alpha (TWA) topsides and jackets, the integrated production facilities (IPF) module, two flare jackets and monopile. Pioneering Spirit will return to the Tyra field to remove the TWA jacket in 2021 and the TEA jacket in 2022.
In June 2020, Pioneering Spirit removed the 17,000-tonne topsides from Shell UK’s Brent Alpha platform in the North Sea, transporting the 40-decade-old structure to Able UK Limited’s Teesside yard in North East England for dismantling and recycling.
Record-setting year for decom
“In 2020, Heerema removed more decommissioned offshore infrastructure than had ever been achieved by a single contractor in one year,” says Heerema Marine Contractors spokesperson Sarah Killoh. “The total amount removed was 85,277 metric tonnes of steel, which will now be recycled at yards in the Netherlands, the UK, and Norway.”
Capping off its busy year in decommissioning, Heerema Marine Contractors (HMC) reported in December its deepwater, semi-submersible crane vessel (SSCV) Thialf completed an eight-month campaign supporting the removal of the Sable Project’s offshore facilities in eastern Canada.
The decommissioning work, undertaken on behalf of ExxonMobil Canada, entailed the engineering, preparation, removal and disposal of seven platform topsides, seven jackets and 22 conductors off the coast of Nova Scotia. Five barge loads carrying Sable platform components, weighing approximately 48,000 tonnes, were towed across the Atlantic by the Heerema tugs Kolga and Bylgia, each of which has a bollard pull of about 200 tonnes.
“We had no Covid cases; it was a great success”
HMC reported an onboard crew of approximately 300 international and domestic workers, aided by support vessels and helicopters, completed the work. While it faced challenges due to the global pandemic, HMC said the removals campaign involved multiple crew changes and was completed safely without a single case of Covid-19.
Ms Killoh says: “[HMC] handled crew changes safely and responsibly, and for the Sable project we had a quarantine system in place to enable our team to enter the country and then board Thialf safely. We had no Covid cases, so it was a great success.”
Components from the project were typically transported from the Sable Field to Chedabucto Bay to be sea-fastened before their transatlantic voyage to the decommissioning yard. After dismantling at the Able UK decommissioning yard in Hartlepool, England, 99% of the material will be recycled primarily into steel.
Developed in the late 1990s, the Sable Offshore Energy Project produced more than 2Tn ft3 of natural gas and liquids during its lifetime, until it ceased operations on 31 December 2018.
The Sable Project was one of six decommissioning and removal projects supported by HMC in Canada and the North Sea using its highly capable offshore heavy-lift and construction vessel fleet. In the North Sea, the world’s largest SSCV, Sleipnir, was deployed for five projects: the Cat3 Ekofisk Ekoa topsides and jacket removals and Jotun-B jacket removal in the Norwegian sector, the Shell Brent Alpha jacket removal in the Scottish sector and Total Tyra Removal phase in the Danish sector.
Work at Sable could provide valuable lessons and inform other ExxonMobil decommissioning projects around the world, most notably for the non-producing platforms in Australia’s Bass Strait.
At one time, the 201.6 m, 198,750 tonne displacement Thialf was the largest SSCV in the world, until it was dethroned by its big sister, the DP3, 220-m Sleipnir in 2019. While not as large as Sleipnir, the dynamic positioning class 3-capable Thialf can perform tandem lifts of 14,200 tonnes.
HMC’s heavy-lift assets are not solely dedicated to decommissioning work. Far from it; in December, for example, Heerema’s heavy-lift vessel Aegir transported and installed the 1,650-tonne water handling module from the MMHE yard in Johor, Malaysia, and installed it on the Woodside-operated Pluto Alpha platform in Western Australia. Previously, the heavy-lift vessel went on contract in Qatar’s largest offshore oil field, transporting and installing three topsides and three bridges for the North Oil Company’s Al-Shaheen Gallaf Project located around 80 km north of Ras Laffan, Qatar.
Aegir is undergoing upgrades in Singapore in preparation for work in 2021.
While declining to go into further details about decommissioning projects for this year, Ms Killoh provided an upbeat assessment. “2021 will be another busy year for Heerema Decommissioning, with projects across the North Sea and also in the Gulf of Mexico, with Sleipnir, Thialf, and Balder all performing decom work throughout the next 12 months,” she says.
Decommissioning projects in the UK North Sea will continue to drive utilisation for high-value assets such as heavy-lift, construction and crane vessels in the years ahead.
Spend on North Sea decommissioning is forecast to surpass £16Bn (US$22Bn) over the next decade, according to WoodMackenzie. In 2021, some US$1.5Bn will be spent on decommissioning 29 hubs in the UK North Sea, about half of which will be undertaken by oil majors ExxonMobil and Shell, Spanish energy company Repsol, UK independent Premier Oil, China’s Sinopec and the UAE’s TAQA.