Mention oil, gas and the North Sea to most observers, and it is likely to evoke memories of a great British success. The discovery of those vast reserves provided a degree of self-sufficiency that became something of a national badge of pride. Yet nothing lasts forever. After 40 years of operations that yielded around £30 billion in revenue, almost all the economically recoverable reserves of oil and gas have been tapped and, in line with UK legislation, the Brent Field is now deep in the throes of being decommissioned.
Production from the Delta platform was suspended in December 2011, with all of its 48 wells then plugged and abandoned. Both Alpha and Bravo ceased production in November 2014, while Charlie is expected to follow suit soon.
How big a challenge is this task likely to be? According to global energy and consultancy group Wood Mackenzie, the oil industry is forecast to spend £15 billion over the next decade on decommissioning in Britain alone and, by the early 2020s, annual costs for dismantling fields may well exceed new investment.
“Many consider decommissioning a North Sea problem, but it is quickly becoming one of the biggest issues in the global oil and gas industry today. For obvious reasons, mature regions such as the North Sea, Asia Pacific and US Gulf of Mexico (deep water) are at the forefront. But the pioneers will set the tone for what is essentially an emergent industry in itself,” says Wood Mackenzie.
More than 700 fields globally are expected to cease production during the next five years, with the top 10 companies forecast “to spend US$14 billion from 2018 to 2022 on decommissioning”. This represents a huge opportunity for the supply chain – not least Hartlepool-based dismantling and disposal contractor Able Seaton UK, which secured the contract to deconstruct the four Brent platforms, with the goal of recycling and reusing their constituent parts to the maximum degree possible. Prior to decommissioning, potential ways to re-use the platforms were explored, from carbon capture and storage facilities to wind farms – and even offshore prisons and casinos. However, the age of the infrastructure, its distance from shore, the lack of demand for re-use, as well as the cost of modernising the facilities, made any such options prohibitive.
First, though, came the actual shutdown and recovery. That challenge started with the Shell Brent Delta platform, which, as is the case for all four platforms, had ‘topsides’ visible above the waterline, housing the accommodation block and helipad, as well as drilling and other operational areas.
“The topsides sits on much taller supporting structures, or ‘legs’, which stand in 140 metres of water and serve to anchor the topsides to the sea bed,” states Shell UK. “After completing the comparative assessment process of feasible decommissioning options, the recommendation was to leave in place the gravity base structures, Brent Alpha footings, the drill cuttings and GBS cell.”
Remarkably, the 24,200-tonne Brent Delta platform, which had served as a hotel for over 160 staff, a factory and a processing plant (and whose deck space platform was almost the same size as a football pitch), was removed in one piece. This was achieved during a highly complex and ground-breaking operation, using the largest construction vessel ever built, the Allseas Pioneering Spirit Allseas Pioneering Spirit, the length of six jumbo jets, marking the world’s heaviest offshore lift, by the world’s largest vessel.
The Brent team had undertaken five years of intense engineering and study work, as well as two years of platform engineering preparations offshore, to strengthen the underdeck and cut the legs on Delta – and then a mere 10 seconds to complete the lift (video at https://is.gd/ifewup).
After arriving off the North East coast, the topsides was transferred to a 200 metre-long barge, the Iron Lady, and then skidded on to Able Seaton Port’s new multi-million pound Quay Six, close to the mouth of the River Tees and one of the strongest in Europe, where at least 97% of the material is in the process of being recycled.
The process employed by Able UK was to dismantle the structure into sections, so these could then be lowered to the ground where it would be safer and easier to dismantle them. This involved partially cutting the internal and external walls through a variety of ‘hot’ and ‘cold’ cutting techniques. They include:
● Oxygen and propane-fuelled cutting torches, because of their efficiency, accuracy, cost-effectiveness and safety when cutting metals
● Angle grinders: abrasive wheel hand-held cutting tools
● Reciprocating saws: hand-held cutting tools fitted with saw blades, for cutting wood, plastic, small cables and pipes
● Hand tools for cutting small items, such as cables and pipes.
Cut and pull
“The partially cut internal and external walls are then connected by wire ropes to a large vehicle, such as an excavator,” explains Able UK operations director Andrew Jacques. “This slowly moves away, forcing the section to part from the topside and fall in a controlled manner into a designated drop zone. A thick bed of sand was laid near the topsides to absorb the shock of these falling sections.
”Cut-and-pull is generally regarded as the safest method for topside demolition and dismantling, particularly since it minimises the number of man-hours spent working at height.”
Onshore dismantling work, featuring a number of excavators fitted with grapples, rippers and shears, then reduces the topsides into its component materials, or waste streams. “These are segregated and stored on site before being transported to other onshore facilities for re-use, recycling or disposal, as appropriate,” adds Jacques. “On the basis of the present topsides inventory, the plan is to recycle at least 97% by mass of topsides material returned to shore, with all material tracked from its present offshore location to its final destination.”
A platform that was three or four decks high has now been stripped down. Most of the accommodation block, the flare stack and the helideck have all been dismantled. Pumps are being refurbished, and over 12,000 tonnes of steel have already been cut to a size that will fit into any blast furnace across the planet for resale. Able UK is even selling the sand it dug up when strengthening the quayside, in preparation for the arrival of the Brent Delta platform at its Hartlepool yard.
Indeed, since the Brent Delta platform came ashore for dismantling, its past and present owners have found there isn’t much that can’t be reused or given away: bedding to an animal charity, mattresses and furniture to people in need, and emergency Marks and Spencer tinned food supplies to food banks – just about everything is of value to someone. With dismantling now around 70% complete (as of late October), it is anticipated that the platform will have completely disappeared by the end of this year.
Shifting the mould-contaminated coffee cups that were left in the galley ahead of the rig’s removal also proved tricky. Yet it seems they were given a smooth ride to Teesside aboard Allseas’ huge single-lift vessel. “One thing that amazes me is how the Pioneering Spirit lifted Delta and put it on the quay and the cups were still in the same place where they had been left,” says Alistair Hope, Brent decommissioning project director at Shell.
“If you approach decommissioning with a mind-set that it is just like production or capital projects, then you are going to get traditional costs and performance. But every time we’ve broken that cycle, we’ve been able to make step-changes in safety and costs. Decommissioning is a fantastic playground for that. We have taken several billion pounds out of the costs through learning how to do things better.”
Neil Etherington, Able’s business development director, also feels good about the project. He adds: “The sheer task of getting the Brent Delta to Able Seaton Port was a triumph for everyone involved – especially partners Shell and Allseas – with whom we have worked for several years to meet the huge technical challenges involved. This has called for a big commitment on our part; we have invested around £28 million in the new quay and associated developments, which offers Able the potential to be at the forefront of a business that is set to grow to meet the need to decommission platforms as they come to the end of their operational lives.”
On which note, the dockyard will be undertaking the same decommissioning process for the remaining Shell Brent topsides. Bravo is due to be delivered to Able Seaton Port in mid-April 2019, then Alpha the following year, with Charlie completing the quartet, probably in 2021-22.
And in October this year, it was confirmed that Able has also been awarded the dismantlement, recycling and disposal of offshore natural gas platforms from the ExxonMobil Canada-operated Sable Offshore Energy Project (SOEP) off the coast of Nova Scotia, Canada. The first shipment of structures is scheduled to arrive with Able UK in the second quarter of 2020. The appointment was made by Heerema Marine Contractors, themselves contracted by ExxonMobil to undertake the removal of facilities.
Comments Jacques: “The project will involve the removal of seven platforms and their jackets, using one of the biggest crane vessels in the world, the Heerema Thialf, with the components being transported to Able Seaton Port in a series of barge movements. We expect that the onshore dismantlement, recycling and disposal work will extend over a 10-month period.”
1971 Shell discovers oil 200km east of Lerwick, Scotland; it is named Brent Field
1976 Brent Delta installation completed
1977 Brent Delta production begins. Pipelines are laid to St Fergus and Mossmorran, said to be the world’s largest single welded pipeline at that time
1979 Oil from Brent pumped to Sullom Voe oil terminal in the Shetlands
1982 St Fergus Gas Plant receives first gas from Brent field. Production peaks at 26.6 million m3 gas/day and 504,000 barrels of oil
1993 Announcement of Brent Redevelopment Project to switch from production of oil to gas
1994 Proposal to decommission oil storage structure Brent Spar by moving it into deep water is withdrawn. Much of the structure is later reused in harbour construction in Norway
1997 Brent Delta redevelopment completed
2006 Establishment of Brent decommissioning project
2007-09 Stakeholder engagement
2010 Shell awards Wood Group PSN decommissioning support contract
2011 Delta production ceases; decommissioning preparation begins
2013 Allseas wins single lift vessel contract for Brent Alpha, Bravo and Delta topsides, as well as the Alpha jacket structure
2014 Able UK wins recycling contract for Brent Delta. Brent Delta wells are sealed. Alpha and Bravo also cease production
2015 Brent Delta topsides decommissioning programme submitted to government and approved