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Storing up safety concerns

Large-scale carbon capture and storage (CCS) using underground structures on the NCS could be close at hand. But transporting and injecting carbon dioxide calls for knowledge of potential HSE threats if it is to help reduce greenhouse gas emissions safely.

Sub-surface sandstone formations from the Jurassic period could soon become storage facilities for massive volumes of carbon dioxide released when burning fossil fuels.

Consumption of such fuels is regarded as the biggest source of human-related carbon emissions, with petroleum operations and energy-intensive industry accounting for a large proportion. Carbon storage in geological structures beneath the seabed could be crucial for reducing emissions from fossil energy sources.

A CCS pilot project has been under way since 1997 on Norway’s Sleipner East fi eld in the North Sea, with the captured carbon dioxide stored in the huge Utsira formation.

Both this structure, which extends north and east of the Sleipner fi elds, and the Johansen formation west of Mongstad near Bergen are relevant for future CCS schemes.

The second of these potential stores comprises Jurassic sandstones up to 80 metres thick, which extend in a straight line from the Norwegian coast to beneath the Troll fi eld.

Official calculations suggest that the two structures could accept substantial carbon volumes over a long period from planned CCS projects with a gas-fi red power station at Kårstø north of Stavanger and a combined heat and power station at Mongstad.

“Feasibility studies for CCS have so far focused on assessing realistic methods and economics,” observes Øyvind Tuntland, the PSA’s director for professional competence.

“In other words, little attention has been paid to the safety challenges. And we know that several considerations need to be taken into account in this context.

“Both the government and the petroleum industry need to work actively on securing suffi cient knowledge of these aspects in the time to come – before technology development takes off.” Carbon dioxide is highly corrosive and raises the acidity of water, thereby posing a threat of deterioration for the materials it comes into contact with.

“Corrosion could thereby be a highly signifi cant consideration when choosing pipeline materials for carbon transport,” says Mr Tuntland. “They must be able to withstand and cope with the chemical reactions involved.”

“Since high concentrations of carbon dioxide are toxic, leaks both on land and offshore could potentially have major safety consequences,” he adds.  “It’s unclear at present how carbon leaks should be spotted, and the industry lacks reliable methods for achieving such detection.”

Carbon dioxide can occur in gaseous, liquid or solid form, depending on pressure and temperature.  Under certain conditions, it can enter a “supercritical” phase.

“We don’t know enough about its properties in this form,” warns Mr Tuntland. “These could include loss of surface tension, which may increase the risk of leaks through seals and fl anges.

“So the petroleum industry needs greater understanding of the way carbon dioxide behaves, its properties, and how these could affect the safety of both people and the environment.  “Nor have the long-term effects, such as the risk of carbon leaks from the storage formations, been suffi ciently identifi ed or studied at present.”

“Our job as the safety regulator is to be the prime mover in securing adequate knowledge and good HSE solutions,” Mr Tuntland notes.

“It’s natural in that context to collaborate with regulators in other countries, particularly the UK, and we’re also taking the initiative on independent studies into specifi c issues relating to CCS.

“With the Sintef research foundation, for instance, we’re looking at well barriers and the possibility that these could be affected by carbon dioxide to allow incidents such as leaks.”

He adds that both the government and the industry must get to grips with all aspects of CCS which could pose risks, and gives special weight to the independent responsibility of the companies to ensure that CCS meets an acceptable level of HSE.

“The spotlight must be on safety throughout the chain from design and engineering to operation and maintenance,” he says.

“When materials are to be ordered and contracts placed, all imaginable HSE aspects must be known and taken into account.  We’ve got to be on the ball now – not later.”