Darius V. Snieckus
OGJ Online
The largest and heaviest non-concrete installation in the UK North Sea -- and the first to be removed under the OSPAR 98/3 accord -- is awaiting a decision on its future after being refloated and towed 2 weeks ago to a deepwater decommissioning yard in Digernes Sound on Norway's West Coast.
Whatever the outcome of Phillips Petroleum Co. UK Ltd.'s deliberations as to the reuse or recycling of 110,00-tonne steel gravity-based Maureen Alpha platform -- and the oil company insists that a "full reuse opportunity" is still its first choice -- the installation's decommissioning has assured its place in the annals of offshore history.
Maureen field had produced 200 million when output was halted in October 1999.
Refloating Maureen Alpha from Block 16/29a had always been in the operator's plans for the offshore development. When Phillips designed the installation over 20 years ago, the "unique and unprecedented (removal) operation" had been built into its engineers' thinking. But that is not to say the 3-day refloat wasn't a delicate and painstaking task.
Contracted to Aker Offshore Partner AS, the June 26 operation involved freeing the platform from the seabed by injecting water via newly installed pumps under the bases to create an upward force, while simultaneously deballasting the seawater in the three tanks which form the base of the concrete structure. As the water was pumped out of the tanks, nitrogen was pumped in to maintain internal pressure.
Over 60 hr, Maureen Alpha was slowly released from the seabed and refloated in 95 m of water. The seawater displaced from the installation's tanks was pumped into a tanker and transported to an onshore facility at Sture, Norway, for cleaning and disposal.
Yet the refloat operation is only part -- though a high profile part -- of the Maureen story. Phillips's remaining program to fully decommission the field involves removal and refloating of the articulated loading column, cleaning and burial of the 2.3 km pipeline from the platform to the loading column, and removal of the drilling template beneath the platform for recycling and disposal.
"The decommissioning program addresses all of the facilities on the field and is fully consistent with OSPAR 98/3 and UK legislation," said Maureen General Project Manager Andy Halliwell. OSPAR 98/3 is the 1998 accord that requires the removal of unused offshore platforms weighing more than 10,000 tonnes from the Northwest European Continental Shelf.
"We were ahead of the game, I think, when you consider the platform was designed in the late 1970s, pre-OSPAR, when disposal at sea would have been allowed," he noted.
The field pipeline and 26,000 tonnes of drill cuttings spread in a 0.6 m "pancake" beneath the platform, though not covered by OSPAR, are being dealt with under Department of Trade & Industry 1999 guidelines.
According to Halliwell, Phillips's extensive "geographic, compositional, and environmental" sampling of the 6,000-tonne drill cutting accumulation directly beneath the platform has led the company to believe that there is a strong case to be made for leaving the pile in place. Despite the fact that much of the drilling at Maureen was conducted using water-based muds, Phillips plans to continue monitoring what it believes to be the "most sampled drill cutting accumulation in the North Sea."
Since the £150-million removal project began in 1993, in addition to the spectrum of engineering studies, modeling tests, and other surveys and assessments, Phillips's planning for the decommissioning also included a far-ranging public consultation program involving 250 organizations including Greenpeace, Friend of the Earth, and the World Wildlife Fund.
"It is the first large platform to be decommissioned since these [OSPAR and DTI] guidelines came out and one of the interesting things about the project has been finding our way through this process," said Halliwell.
Before the Maureen owners -- Phillips, Fina Exploration Ltd., Agip UK Ltd., BG Group PLC, and Pentex Oil UK Ltd. -- could proceed with the refloat they had to plug 23 wells. That job went to the PACT Consortium -- a joint venture of UWG, Baker Oil Tools, Baker Atlas, Progentive Services Ltd., Team Energy Resources, and Claxton Engineering.
In July 2000, the consortium, using concurrent operations and rigless abandonment to save time and cost, plugged and severed the production wells below the mudline, and recovered all casings and conductors.
Part of the program involved setting cement plugs downhole across all annuli and within the tubing to permanently seal the reservoir and wellbore from the seabed. For this task PSL carried out cementing and pumping services; Baker Oil Tools provided casing and through-tubing cutting, pulling, and milling, along with inflatable packers, safety valves, and fishing packages; and Baker Atlas supplied specialized perforation and electric line/wireline services. UWG and Claxton handled the severance of casing strings during the operation.
When the one-well Moira satellite facility, 10 km from Maureen, along with its associated pipelines and umbilicals, were removed and brought ashore for recycling and disposal in April the way was clear for the refloat.
With Maureen Alpha's arrival at Aker's dedicated decommissioning facility at Stord, Norway, the first task, according to Aker, will be an inspection to spot any maintenance and improvement needs. Then in the fourth quarter the contractor will begin cleaning the platform's three storage tanks -- which Phillips calculates still hold 18,000 bbl of oil and sludge.
The question remains on Maureen Alpha's ultimate fate. Reuse, following modifications, remains Phillips's preferred option for the platform and Halliwell noted that talks were ongoing with various oil companies to this end. The other option is dismantling -- no small task when one considers Maureen's dimensions: 780 ft high with tanks that are 243 ft high and 84 ft in diameter.
It is an expensive question too, since it will cost £20 million/year to leave the platform moored at the deepwater yard until a final decision can be made.
Halliwell said, "The waste hierarchy says that reuse is better from an energy usage point-of-view than to recycle -- which is also better than disposal, but we currently have no suitable reuse opportunity signed and sealed."
He said Phillips's comprehensive search for a buyer has approached operators around the world where a "technical match" for reuse was identified.
"We talked to hundreds [of companies] and there are a handful of prospects worldwide still viable for Maureen's reuse," he added, "but time is running out for the total reuse option.
"We think we have some very sound partial reuse alternatives even if we can't find one for total reuse," he added.
Whatever the fate of Maureen may be, its removal has established precedents for operations that will become more common in the North Sea in future years.
As Britain's Energy Minister Brian Wilson observed after the refloat, "Decommissioning is an important milestone and is an integral part of the operations of a successful oil province."
Contact Darius V. Snieckus at [email protected]
