The huge job of decommissioning and plugging seven subsea oil wells 50 kilometres off the coast of Victoria entailed months of offshore work and years of careful planning. The big seas and strong winds of the Basker, Manta and Gummy (BMG) fields, with wells located at ocean depths of between 200 and 270 metres, made for a potentially hazardous project.
Last year’s successful BMG decommissioning campaign by Amplitude Energy Limited cost about $270 million and took about 360,000 work hours, but no lost-time injuries or serious safety incidents were recorded.
The campaign entailed sealing the subsea wells with cement plugs. Some of the staff working on the campaign lived on board the Helix Q7000 – an enormous mobile platform-type vessel. The vessel had about 140 beds, and the campaign operated 24 hours a day, seven days a week. Workers were ferried back and forth to the vessel by helicopter and the project averaged about nine helicopter flights a week.
“Every offshore project comes with its own set of hurdles,” says Amplitude’s Chief Operating Officer Chad Wilson. “The BMG decommissioning campaign pushed the boundaries of what’s been done in Australia before.”
Winner of the Wellbeing, Health and Safety category of the Australian Financial Review’s Energy Awards, Amplitude Energy’s BMG decommissioning project required a tailored approach.
“These wells were of a complex design with a few unique design characteristics, so we couldn’t just use off-the-shelf solutions,” says Wilson, a chemical engineer by training who has worked in the oil and gas industry for a number of years. “The engineers, the technicians and the offshore crews had to work together to develop custom tools and also use new technology so the job could be done safely and effectively.”
The BMG decommissioning project was the first time the Helix Q7000 vessel had been used for a full plug and abandonment campaign in Australian waters, he adds. Australian regulations had to be followed and the Helix Q7000 configured for the local conditions. The vessel had specialist equipment that made the project safer and easier to manage.
Amplitude acquired the BMG fields in 2014 years after the wells had stopped producing oil, Wilson says, to take advantage of the fields’ gas reservoirs. The company was then required to decommission the oil wells and return the sea floor to its natural state.
Hundreds of people worked on the BMG decommissioning campaign. About 165 days of offshore work was required to plug all seven wells and Amplitude worked closely with Helix leaders to ensure a unified approach. Early hazard identification was prioritised and “batch methodology” used, so common operations could be completed across all seven wells before moving to the next phase, reducing risk and cost without compromising safety.
An Amplitude team including engineers and technicians worked offshore on the vessel, and the company also relied on its service partners, including the Helix Q7000 crew, Wilson says.
Specialist equipment developed for the decommissioning project included a “re-entry bracing frame” for a subsea tree – the system that controls the flow of hydrocarbons from the seabed to the surface.
“The re-entry bracing frame provided support to the subsea tree so that we could go in and out of it to set these really deep-set cement plugs and do the work that was required to make sure that we restored that geological barrier down in the wells,” Wilson says.
Decommissioning has become increasingly common in the oil and gas industry as equipment ages, Wilson says, and it is now a normal part of the business around the world. The Helix Q7000 arrived in Victorian waters from New Zealand, and then went on to jobs in Western Australia and Brazil.
Australia’s oil and gas industry leaders have expressed a lot of interest in the BMG campaign. “We’re more than happy to share our learnings with everyone,” Wilson says. “The way I look at it is that the oil and gas industry is still going to be needed for a long time, and for Australia to remain competitive globally we need to be willing to discuss how things can be done, better, safer, more efficiently.”
Phase two of the BMG decommissioning project is now in the planning stages. The “flow lines” or pipes laying on the seabed have been flushed and left in a safe state and they now require collection, Wilson says. They might be cut into pieces on the seabed and the pieces then lifted to the ocean surface with grappling hooks and a crane, or the pipes might be wound around a giant reel.
In the years before the decommissioning BMG campaign began, the wells were inspected by undersea robots equipped with video cameras, and found to be stable.
“All the equipment that came up from the sea floor was in incredible shape,” Wilson says. “All of these facilities are built with the mindset that they’re going to be down there for a really long time. So they’re typically over-designed. And if we didn’t think they were going to be in a safe state, we would get on the work a lot sooner.”