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New RNNP report surveys acute discharge risk on the NCS

Both acute crude oil spills from petroleum operations on the Norwegian continental shelf and near misses for such incidents have fallen sharply since 2001, a new study has found.

A summary of the report will be translated into English.

But the RNNP report from the Petroleum Safety Authority Norway (PSA) on acute discharges in 2001-2009 expresses concern at the rise in hydrocarbon leaks and well control incidents during 2009.

The results of the study, which builds on the PSA’s on-going survey of trends in risk level in Norway’s petroleum activity (RNNP), were presented to the Safety Forum on 18 November.

Monitoring such trends represents an important tool in the PSA’s surveillance – pursued in many different ways – of risk developments in this industry.

Much data gathered since 2000 through the RNNP studies on accidents and undesirable incidents in the sector have so far been used to track trends in risk for people and major accidents.

A groundbreaking effort was launched in 2009 to use information drawn from the RNNP and Environment Web databases to monitor developments in acute discharges to the sea on the NCS.

Risk in this connection is confined to frequencies and volumes of acute discharges. The actual and potential environmental consequences of these spills have not bee assessed.

“Part of our job is to contribute to preventing accidents,” says Øyvind Tuntland, the PSA’s director of professional development.

“For us, this is a matter of safety for employees, the natural environment and material assets.

“Trend monitoring based on historical data provides important information about risk development in the petroleum industry, and is actively used to prioritise accident prevention efforts.”

The RNNP data show that the number of crude oil discharges to the sea on the NCS, viewed as a whole, more than halved in 2001-04, while the level remained constant in 2004-09.

A clear annual reduction in acute crude oil spills has been recorded in the Norwegian North Sea, with the biggest fall up to 2003. The decline over the six years to 2009 was more limited.

The Norwegian Sea witnessed an increase in the early part of the period, followed by a substantial reduction and a stable level since 2004.

No clear trend can be discerned for the size of acute crude oil spills in 2001-09 on the NCS as a whole. The picture is dominated by the five largest discharges during this period:

These figures indicate that four of the largest discharges on the NCS in 2001-09 occurred during the last five years of the period.

In addition to acute spills of crude to the sea, data are also available on such discharges involving other types of oil – in practice, primarily hydraulic fluids – and chemicals.

The average volume of acute chemical discharges per installation year was stable in 2001-09, and highest in the Norwegian Sea. Acute discharges from injection wells are also covered by the study.

Near misses
The report not only looks at acute discharges in the petroleum industry during the period, but also analyses near misses which could have led to such spills if several barriers had failed.

That corresponds to the RNNP analysis carried out every year for the risk to people.

The number of near misses which had the potential to cause an acute spill on the NCS declined throughout the 2001-09 period, and was at its lowest per installation year in 2009.

A theoretical “statistically expected” discharge volume per installation year has been calculated to obtain an indication of the trend for the level of seriousness of near misses. This has shown a decline, particularly in the Norwegian Sea.

If the near misses had led to acute crude oil spills, it is estimated that the probability of such discharges being smaller than 1 000 tonnes was more than 70 per cent.

Information on barriers has been assessed on the basis of test data and investigation reports for installations producing both oil and gas.

The effectiveness of barriers to prevent major accidents is considered to be stable at a generally high level for the NCS as a whole.

However, some installations have a substantially lower availability of certain barrier elements than the average for the industry.

Analyses of investigation reports show in part that barriers for well incidents have functioned as intended when required. The exceptions are the Snorre A gas blowout in 2004 and 14 cases of shallow gas blowouts in 1999-2009.

The two types of near misses considered to be of the greatest significance for the probability of acute discharges are well control incidents and hydrocarbon leaks.

Although the latter largely relate in practice to gas escapes, they have been included in this study because they could cause very serious explosions.

These in turn might escalate to cause well damage and thereby acute discharges to the sea. The Piper Alpha disaster on the UK continental shelf in 1988 provides a case in point.

Well control incidents and hydrocarbon leaks were less serious in 2008 and 2009 compared with 2004-06. After a generally positive trend in recent years, however, the fact that near misses for such events rose in 2009 on the NCS as a whole is clearly negative.

“Projects aimed at reducing gas leaks and enhancing well integrity show that good results can be achieved when the industry unites over common safety-critical challenges,” says Mr Tuntland.

“However, both issues need to stay high up the industry’s agenda. The same applies to maintenance improvement processes, one of the most important conditions for sustaining an acceptable technical standard of such aspects as barriers.”

The Macondo blowout in the Gulf of Mexico demonstrated the potential that such incidents could last a long time and produce substantial discharges.

This also represents a relevant risk for the NCS and is reflected in the models applied in the RNNP study.

The highest category for the volume of crude oil discharged to the sea was raised during the work from more than 100 000 tonnes to above 500 000 tonnes in order to give a more refined reflection of the largest potential spills.

Another result of the Macondo blowout has been a more detailed study of incidents involving subsea wells from 1999 to 2009, broken down by different water depths.

Relatively few such incidents have been registered on seabed wells in any one year, and none have developed into an acute discharge to the sea.

Viewed overall, wells in more than 600 metres of water have shown a clearly higher frequency of incidents, statistically significant in most cases, than those in shallower depths.

More detailed surveys of near misses occurring in deepwater operations have so far failed to identify whether water depth alone can explain this excess frequency.

“The Montarau blowout off Australia in 2009 and the Macondo incident this April occurred close together in time,” observes Mr Tuntland. “In a global industry such as the petroleum sector, this must be regarded as a serious wake-up call.

“A number of investigation reports are due to be published, and ensuring that the necessary lessons are incorporate through established national and international fora will be crucial.”

Work on the RNNP report into acute discharges provides an important supplement to the factual basis for prioritising accident prevention work.

In addition to illustrating risk trends on the NCS as a whole, the study has been structured so that each sea area can be viewed separately – allowing it to be used in preparing management plans.

The databases for the North and Norwegian Seas are large enough to be able to draw some area-specific conclusions, but information for the Barents Sea is currently much too limited.

However, activities in the latter waters will, in practice, involve the same players, experience, knowledge and technology as on other parts of the NCS.

Results for the Barents Sea can accordingly be regarded for the time being as similar to those for these more southerly areas.