Against the floe – sea ice and offshore structures11 November 2016
The US Bureau of Safety and Environmental Enforcement (BSEE) and the University of Alaska have collaborated on a study into offshore structures and their ability to survive sea ice in extreme Arctic conditions. BSEE Alaska Region analyst Scott Carr gives his verdict on current design standards.
Eight years is a long time in the oil and gas business. In 2008, with the price of crude at $88 a barrel, multinationals including Royal Dutch Shell, ConocoPhillips and Statoil renewed their focus on Arctic waters, snapping up 2.8 million acres in the Chukchi Sea from the US Government for $2.6 billion, on top of existing leases in the Beaufort Sea.
The business case seemed solid. The US Geological Survey estimates that the area above the Arctic Circle holds 30% of the world’s undiscovered natural gas (1,670 trillion cubic feet) and 13% of its oil (90 billion barrels).
With the oil price apparently buoyant, energy demand spiking and the US shale gas revolution in its infancy, the Arctic represented a calculated risk for upstream operators with big balance sheets.
Fast-forward to September 2015, when Royal Dutch Shell announced that it was abandoning all activity in the region − having spent over $7 billion in the Chukchi and Beaufort Seas − citing disappointing results from its Chukchi test well combined with sky-high operating costs and evolving regulatory standards.The US Government swiftly cancelled two Arctic offshore lease sales and said it would not extend existing deals.
In May 2016, with the price of crude at less than half of its 2014 mark, Shell and its Arctic rivals relinquished a total of 2.2 million acres of drilling rights in the Chukchi Sea, well over 80% of the leases purchased eight years ago.
For now, at least, Big Oil’s final frontier remains unconquered.
That is not the end of the story, however. A rise in the oil price to $80−90 (roughly double the mark for Brent crude at the time of writing) could theoretically make exploration and production (E&P) in the US Arctic viable again for multinationals with deep pockets and a long-term strategic vision.
In the Norwegian Arctic, Eni’s Goliat FPSO in the northern Norwegian Barents Sea started production in March 2016, and is due to hit about 100,000 barrels a day at its peak, while in Russia Gazprom Neft’s ambitious plans for the rich Prirazlomnoye field on the Russian Arctic Shelf involve 36 wells.
For future E&P activity in the US Arctic to succeed, offshore infrastructure must be resilient enough to survive first and multiyear sea ice in extreme conditions.
Cold, hard facts
A recent collaborative study by the US Bureau of Safety and Environmental Enforcement (BSEE) and the University of Alaska took a forensic look at current offshore structural parameters and the federal standards that govern the industry.
The objective of the two-year research project titled ‘Reliability-Based Sea Ice Parameters for Design of Offshore Structures’ was to produce information that would supplement current standards and regulations, and provide valuable additional sea ice data related to the Chukchi and Beaufort Seas.
Data from 16 seasons provided comparisons of parameters such as first and last ice occurrence, ice level, rubble fields, ridges and ice movement. The team was then able to study a range of annual values in order to develop averages from which to draw conclusions.
“The study had multiple objectives, but – in a nutshell – BSEE was looking to fill in some of the data gaps that it had identified in ‘ISO 19906 Standard: Petroleum and Natural Gas Industries – Arctic Offshore Structures’, and also to see if the structural design criteria in ISO 19906 was conservative enough for future Arctic structural design,” says Scott Carr, the analyst in charge of BSEE’s studies programme.“Sea ice is probably the most severe environmental factor that we face in the Arctic, and the threat it poses isn’t just confined to offshore structures, but also covers damage to oil and gas pipelines,” he adds.
In the Barents Sea and the Russian Arctic, for example, grounded icebergs and those caught in tidal currents threaten underwater installations and pipelines.
A significant number of very large icebergs are also produced around the Greenland continental shelf, while smaller masses (known as growlers) are also risky, because they are heavy and difficult to observe using satellites and ship radar.
Summer Arctic sea ice is not only melting more quickly, but is also becoming younger and thinner. Predicting the behaviour of this more recent, faster-flowing ice, and its potential impact on oil rigs and related infrastructure represents a key challenge for the offshore industry in the decades ahead.
“In 2012, Royal Dutch Shell halted operations at the Burger-A well in the Chukchi Sea due to the unexpected movement of a 30-mile-long ice floe near the Hanna Shoals,” notes Carr.
“Shell decided to carry out a planned disconnect and its return to the area was delayed due to continued sea ice.
Sea: the difference
“Since 2009, BSEE has been involved in a study looking at the rapid changes taking place in the Arctic, including how much later in the season the area is freezing up, as well as the ultimate limit of first year and multiyear sea ice.
Its recent collaboration with the University of Alaska looked at what is currently being observed in the Arctic, and what sea ice science is predicting for the future, as well as whether or not the design criteria in ISO 9906 is sufficiently conservative to account for such changes.”
The study describes the current implementation of ISO 19906 in US waters as “questionable”, due to a lack of sea ice design criteria and assesses the suitability of the current recommendations for estimating global ice forces on offshore structures, with a particular focus on pressure ridges – the term given to angular ice blocks of various sizes that pile up when two or more floes meet.
Pressure ridges are significant for three reasons. Firstly, they represent the highest loads placed on offshore structures by drift ice.
Secondly, ridged ice makes up around 40% of the overall mass of sea ice and so impacts navigation.
Finally, when pressure ridges drift into shallower areas, their keel – the part of the ridge below the surface − may come into contact with the seabed and threaten subsea pipelines.
“The primary investigator noticed that the pressure ridge keels in the Beaufort and Chukchi Seas appeared to follow a predictable mathematical pattern, and this information is extremely beneficial,” Carr explains.
“The BSEE study identified critical keel depth, and historical sea ice data was analysed in terms of temperature pressure, ice profiling, sonar anomalies, changes in density, and sound-speed profiling in the water column.
Further analysis focused on different sea ice features. The researchers concluded that the current standard of practice cited in ISO 19906 was conservative for contemporary structural design parameters, and that current offshore structures could withstand sea ice.”
The results of the study were presented to representatives from six Arctic nations during the Arctic Offshore Regulators Forum in Washington, DC, in April. Seven studies are currently assessing offshore engineering technology and the conditions operators face in harsh Arctic conditions.
Shell is no longer working to extend leases that begin to expire in 2017, and has held onto just one tract in the Chukchi Sea. Carr hopes that the BSEE study will inform future offshore operations, if and when the US Government decides to sell leases in the Beaufort Sea in 2020 and the Chukchi in 2022.
“We are looking to the future,” he says. “BSEE will use the information from this study and others to develop Arctic-specific infrastructure regulations developed for the Alaska Outer Continental Shelf.
“This project was designed to get us ahead of potential issues that may occur in the future.”