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Staying power

Atkins | 04 Dec 2008 | Comments

Damage to an oil and gas installation can present a serious safety risk, but closing for repair has massive cost implications. How do operators ensure they shut down only when absolutely necessary?

When, on 13 September 2008, Hurricane Ike struck the Gulf of Mexico with winds of up to 74mph, the damage was extensive. The US Minerals Management Service reported that 52 of the 1,450 exposed offshore oil production platforms were destroyed and a further 29 were severely damaged. But it could have been even worse.

“While the full impact of Ike is still being calculated, recent work to improve structural safety may mean the damage was not as severe as in past hurricanes. The lessons will take time to emerge,” explains Atkins’ Martin Grant. Grant is managing director of Atkins’ energy business, which has operations in some of the world’s major oil and gas hubs, including: the UK (Aberdeen and London); the US (Houston, Texas); Trinidad; United Arab Emirates (Sharjah); China (Shanghai); and Australia (Perth).

Force of nature

Between 2004 and 2005, hurricanes in the Gulf of Mexico, including Hurricane Katrina, destroyed 113 offshore oil platforms and seriously damaged a further 52. Since then, Atkins has worked to learn from these storm events and has revised design standards to ensure that structures cope better in the future.

“In some locations, the waves were hitting the offshore oil platforms higher than expected,” explains Dr Ramsay Fraser, a director in Atkins’ energy business and an expert in offshore structures.

“When a platform is designed, the deck is normally positioned out of reach of the wave crest, but at some we found the waves were hitting the deck. This can be very serious,” he explains. “Normally when a wave hits the tubular steel bracing of a platform’s legs it has a limited effect, because water passes through the vast openings. But when they hit a solid deck, the force can be huge and can push the structure sideways. This impact can severely damage the platform.

“Some platforms from the 1960s and 1970s don’t have enough deck clearance or strength,” says Fraser. “In the revised design, the decks will sit higher above the surface and the tubular bracing may be stronger.”

Platform operators with offshore installations in the Gulf of Mexico have been reviewing their fleets in light of this new knowledge.

The long-term view

For the UK, maintaining its North Sea oil platforms as safe working environments is a real challenge. “There are a number of installations in the North Sea that were only designed to last for 20 years,” says Grant. “We now want them to last much longer.”

But degradation of these installations is a fact of life. “There are around 200 structures in the UK’s part of the North Sea and they are regularly battered by wind and waves, while immersed in corrosive saltwater. As a result, some develop defects on a regular basis,” says Grant.

Assessing the extent of such defects and the safety risk they present to workers is essential in deciding whether it is necessary to repair the installation, which can mean halting production.

In the past, however, these calculations have been over-cautious with the risk of unnecessary shut down of offshore infrastructure.

“Structural resistance was calculated by checking the capacity of each component, and the force applied on it,” says Fraser. “However, in recent years, new software and mathematical techniques mean we can assess the whole structural system. This is important: while one component may yield or buckle, there could be enough resistance in the structure as a whole to prevent collapse. We’ve discovered that these structures are actually more resilient than once thought.”

Damage limitation

As oil prices can fluctuate dramatically, halting production for any reason is incredibly expensive for producers. “Profits have increased dramatically along with the price of oil, so there is massive pressure to keep the platforms in operation,” says Grant.

Proving that offshore infrastructure is safe enough to stay operational means activities can continue while defects are repaired, which can have huge cost-savings for the operators. “For some of the biggest installations, lost production would be around $10,000,000 per day, so shut-down would be catastrophic,” says Grant.

Considering the potential financial losses of halting production, it’s unsurprising that operators try to keep platforms operating despite the damage. But, thanks to recent advances, doing so is now a much safer and less costly option.

Oil rigs: in the long term

According to Professor Alexander Kemp of the University of Aberdeen Business School, oil and gas infrastructure is going to play a key role in the evolution of the whole industry over the coming years.

“Looking ahead, the average size of new oil field development will gradually fall from its present size of around 20 million barrels of oil equivalent,” he says. “The development of small fields can be economically challenging even with high oil and gas prices, and the presence of readily accessible infrastructure can constitute the difference between a viable and non-viable project.

“The prolongation of the life of the present infrastructure is highly important in promoting new field developments. There can be a virtuous circle here: the more new developments that come forward, the longer the economic viability of the infrastructure. There will also be greater incentives for the asset owners to undertake investments to extend its life. Enhancement of the integrity of the infrastructure will also help to ensure that there is less likelihood of technical problems resulting in temporary shut-downs with their adverse effects on production.

“One of the few advantages of a mature petroleum province is the presence of an efficient infrastructure network and maximising its economic life is in the interests of all stakeholders.”

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