Large structures in deep water Gulf of Mexico are set to challenge established decommissioning methodologies in the basin, while the North Sea still awaits its bow-wave of activity. Elaine Maslin reports.
Globally, the offshore decommissioning market has largely been limited to two basins, the Gulf of Mexico and the North Sea.
Both are facing challenges. For the Gulf of Mexico, which has an established decommissioning supply chain, experienced in removing hundreds of platforms a year, the move to removing structures from deeper waters will be the key challenge in coming years.
Image Caption: ExxonMobil’s Harmony platform jacket, which stands in 1198ft water depth in the Pacific Outer Continental Shelf. Photo: US Dept. of Interior, BSEE.
For the North Sea, the challenge is aligning the supply chain and available capacity to an ever shifting cessation of production date, against high demand from greenfield projects and the emerging offshore wind installation market.
US
The US Gulf of Mexico has an established decommissioning market, with about 4100 of approximately 7000 structures removed to date.
Annually, about 150-200 structures are removed per year, says Robert Byrd, vice president, consulting, of Houston-based TSB Offshore. Most weigh less than 2000-tonne and are typically removed in single lifts.
The decommissioning market benefited from “idle iron” regulations, brought in post-2005, when hurricanes Rita and Katrina damaged or destroyed close to 200 platforms. The iron regulations require operators to remove non-operational facilities after set periods of time.
This increased decommissioning activity, from about 100 facilities per year to closer to 200, says Byrd, bringing contractors close to capacity.
The US market also benefits from a relatively smooth decommissioning process, enabling it to plan and start executing decommissioning projects in months, as opposed to years in the North Sea, says Byrd, who was speaking at the Offshore Decommissioning Conference in St. Andrews, Scotland, in October.
This is not because the regulation is different—both regimes are quite similar, apart from additional post-decommissioning monitoring requirements in the UK, he says. The difference is that in the US operators work through one agency, which co-ordinates the different studies,Sea, says Byrd, who was speaking at the Offshore Decommissioning Conference in St. Andrews, Scotland, in October.
This is not because the regulation is different—both regimes are quite similar, apart from additional post-decommissioning monitoring requirements in the UK, he says. The difference is that in the US operators work through one agency, which co-ordinates the different studies, applications and processes. In the UK, the operator deals with the different agencies, from the Department of Energy and Climate Change (DECC) to the Coast Guard.
Gulf of Mexico challenges
The Gulf of Mexico is facing some large challenges, however. Operators are beginning the process of decommissioning larger structures in deeper waters—jackets typically in excess of 10,000-tonne, in water depth greater than 1000ft (312m).
“A number of these facilities are getting into pre-feed phase of decommissioning and in the coming 3-5 years we will start to see some of these platforms start to come out,” says Byrd. “This is going to be a significant challenge for us.”
The challenge, he says, is the methodology used for the removal. “Our bread and butter is single piece jacket and topsides lift,” he says. “These larger structures will not lend themselves to that process.”
The Lena guyed tower, for example, is 1025ft in length, weighing 25,000-tonne. The Cognac platform, which was the first in excess of 1000ft jacket installed, he says, was installed in three pieces.
“We simply haven’t really addressed the technology that’s required for decommissioning these structures.
“One of the things the hurricanes did for us, in 2005, is push us in to development of new and better technology for heavy lift, and particularly for lifting large weights off the bottom in water depths of 300-400ft. But that still doesn’t get us into the type of lifting technology for these 1000ft plus jackets.
“Piece small removal will very likely be required. But, while you talk here in the North Sea about small piece removal as a standard way of doing things, it’s actually quite new for us in the Gulf of Mexico.
“The piece small process also presents challenges logistically— how to deal with the actual lifting and cutting. It’s going to be a real opportunity for the contractors providing cutting services and ROVs.”
The Gulf of Mexico does have the benefit of a strong reefing program, unlike the North Sea or the Pacific Outer Continental Shelf. It is likely that the very large jackets due to be removed will be reefed, says Byrd.
Since Louisiana’s artificial reef program began in 1986, 71 offshore reefs utilizing the jackets of 320 obsolete platforms have been created off Louisiana’s coast. Gulf-wide, more than 400 obsolete platforms have been converted into permanent artificial reefs, according to the state Department of Wildlife and Fisheries.
Many of the same issues are arising in the Pacific Outer Continental Shelf. Here there are 28 platforms, all quite large. “These will all be a challenge for us,” says Byrd.
“In places like California, the barge transportation will be far more complicated than we have to deal with to date, because there is virtually no infrastructure.
“Creating infrastructure for large structure decommissioning is going to be a challenge everywhere. Even in the Gulf of Mexico we do not have the onshore facilities that are required to support the removal of some of the very large structures. In California there simply is no infrastructure at all.”
UK
While the US market is wellestablished, the UK’s North Sea Continental Shelf (UKCS) decommissioning market is still agonizing over when the anticipated bow-wave of decommissioning activity will start.
There are 297 platforms in the UKCS, according to the UK Government. A Royal Academy of Engineering report in 2012 says 31 of those have large steel jackets weighing more than 10,000-tonne, and eight have large concrete substructures. According to a survey of 27 UK North Sea operators (representing 87% of basin activity) by Oil and Gas UK, about £10.4billion will be spent on decommissioning over the next 10 years, peaking 2015-2019—a period later than the previous year’s survey predictions.
This will include 2300km of pipelines, infrastructure in 74 fields, 800 wells, more than 70 subsea projects and more than 130 installations, says the report, released at the St Andrews conference. The majority of the cost, 44%, will be in the deeper, harsher northern North Sea, with 32% in the central North Sea and 24% in the southern North Sea and Irish Sea.
Most of the cost, 43%, is expected to be spent on plugging and abandoning (P&A), with a further 21% on removal and 19% on overheads. The remaining cost will be on topsides preparation and making safe facilities and pipelines.
Average costs of well P&A in the northern and central North Sea, based on current spending, were estimated as £4.7 million for a platform well, £8 million for a subsea exploration and appraisal well, and £10.1million for subsea development wells.
In the southern North Sea and Irish Sea, average costs were estimated as £3.5 million for a platform well and £6.6 million for subsea wells, of which there are fewer.
The limitations in the North Sea are seen to be not having enough heavy lift vessels with the capacity to lift and remove the tonnage expected.
“If we look at the limited number of successfully decommissioned platforms to date, removal has been limited to below 5000-tonne,” says Abigail Clark, analyst at Oil & Gas UK, also speaking at the conference, organized by Oil & Gas UK and Decom North Sea.
“A number of steel structures ranging from 4000-20,000-tonne have been approved for fabrication and many of these are expected to be ready for production before 2017, so competition for heavy lift vessels is expected to be high also, although flexibility in decommissioning is expected to alleviate this.”
Capacity for onshore disposal, with 405,000-tonne expected to land on shore in the next 10 years, is thought to exist, but it has yet to be tested on management of materials, according to a Decom North Sea study.
A further capacity constraint is for rigs, already in demand for production, exploration and appraisal well drilling, associated services and human resources. The UK industry is also behind the Gulf of Mexico in understanding the longer term effects of offshore installations on the North Sea eco-system.
“Through JIPs and work with Decom North Sea, there is a realization we don’t know much about the interaction of installations with the North Sea eco system,” says Mick Borwell, Oil & Gas UK’s environmental issues director. “The Gulf of Mexico does, but the North Sea is different. We need to acquire new knowledge.”
A scientifically independent research initiative, Insight, has now been launched to address this, added Borwell.
International
Outside the Gulf of Mexico and the North Sea, there are only potential markets, in places like West Africa, Middle East, India, south Asia, and southeast Asia, says Bryd.
“There are thousands of wells that have been suspended and dozens, if not hundreds, of platforms currently idle, particularly in places like the Gulf of Thailand,” he says. “The problem in the broader international market is the lack of clear and firm regulations.
“This is an issue that is evolving, particularly in southeast Asia. A group of Asian countries recently adopted a broad outline for decommissioning regulations, but they have not been implemented. This is standing in the way of seeing a lot of actual decommissioning taking place.
“The other impediment, and perhaps an even more difficult issue to resolve, is the national oil companies, who are generally involved very heavily in places like Indonesia, and to some extent Malaysia and Thailand, are very reluctant to spend the money required on decommissioning.” OE
Image Caption: CNR’s central North Sea Murchison platform.
The Murchison platform is in Block 211/19, northern North Sea in 156m water depth. First production was in 1980.
It stands on an 8-legged steel jacket, weighing 24,640-tonne, excluding piles. It is a candidate for OSPAR derogation, which means part of the jacket could be left in place.
The topsides comprise 26 modules, weighing 24,584- tonne. It has 34 wells, one of which is subsea. It also has subsea infrastructure. Murchison’s total height is 254m (833ft).
Aker Solutions was recently awarded a three year contract for the engineering design, procurement and offshore execution to prepare the facilities for removal. The estimated landing to shore of material period is 2015-2021.
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