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RNNP report: Development in risk of acute spills on the Norwegian shelf 2001-2011

During the period 2001 – 2011, there was a clear reduction in the number of acute crude oil spills to sea on the Norwegian shelf. Leaks in and damage to flexible risers continues to be an unresolved problem area, which will require attention from the industry in coming years.


The Petroleum Safety Authority Norway (PSA) monitors the risk development in petroleum activities in several different ways. An important tool in this connection is the mapping work within 'Risk level in Norwegian petroleum activities' - RNNP.

Download the report: Development in risk of acute spills on the Norwegian continental shelf 2001-2011 (In Norwegian only)

Since 2000, RNNP has gathered extensive data material on accidents and undesirable incidents in the petroleum activities. Initially, the data was assessed to follow up the development in risk of major accidents and personal injuries.

In 2009, work started on utilising parts of this data material and parts of the Environment Web database to also monitor the development in risk of acute spills on the Norwegian shelf. In this context, risk means frequencies and volumes of acute spills. The spills’ actual and potential consequences with regard to environmental damage have not been assessed.

Development – actual spills
During the period 2001 – 2011, there was a clear reduction in the number of acute crude oil spills to sea for the entire shelf, both expressed as the number of incidents per year and the number of incidents per facility year. Following a steep decline at the beginning of the period, the number of spills has remained at a stable level in the years 2004–2011.

 

Figure 1 shows the number of acute crude oil spills to sea, per facility year, and the total number, the entire Norwegian shelf during the period 2001–2011.

There were 34 acute crude oil spills to sea in 2011, where 24 and ten took place in the North Sea and the Norwegian Sea, respectively. During the entire period, the number of acute crude oil spills per facility year has been lower in the North Sea than in the Norwegian Sea. The frequency per facility year is, on average, nearly 86 per cent higher in the Norwegian Sea.

 

Figure 2 shows the volume of acute crude oil spills, in total and per facility year, on the Norwegian shelf during the period 2001-2011.

The volume of crude oil in the sea as a result of acute spills has varied. It is difficult to see a trend for the Norwegian shelf. The majority of the spills, 98 per cent in the North Sea and 95 per cent in the Norwegian Sea, can be placed in the lowest spill category (0-10 tonnes). There is considerable variation in the spill volume for both the North Sea and Norwegian Sea, but the average spill volume for the entire period is higher in the Norwegian Sea than in the North Sea. There was one crude oil spill in the Barents Sea during the period 2001-2011. This spill was in the lowest category in 2001.

Given that this time period is relatively short (ten years) and that major spills have occurred, a general consideration might be that, while large spills are rarer, they do occur. It is also not impossible that larger and even rarer spills could occur unless extensive work is carried out to prevent this.

In addition to acute crude oil spills, the RNNP-AU report also addresses other types of spills, other oils, chemicals and discharges from cuttings injection.

Development – near misses
RNNP-AU also analyses development over time of near-misses that could have led to acute spills if more barriers had failed. For the Norwegian shelf overall, there is a reduction in the number of near-misses during the period. It appears the level of number of incidents will decline from a stable higher level at the beginning, to a stable lower level during the last half of the period.

Figure 3 shows the number of registered near-misses and a three-year rolling average of the number of near-misses that could potentially lead to acute crude oil spills on the Norwegian shelf, normalised over the number of facility years.

Despite the reduction in the number of near-misses on the Norwegian shelf, the relative risk indicator for potential number of acute spills shows a significant increase. The cause is a clear increase in the last four years in the relative risk indicator for acute spills related to leaks in and damage to flexible risers and subsea installations (DFU9).

Figure 4 shows the relative risk indicator (per year and three-year rolling average) for the potential number of acute spills on the Norwegian shelf, normalised over the number of facility years, where the indicator value in 2005 is equal to 1

The value for the risk indicator in 2011 is the highest in the period and the increase from 2010 is considerable. Eight serious cases of damage to flexible risers were reported in 2011, in addition to two leaks.

Flexible risers are critical components with the potential for major accidents, and data from RNNP shows that they have contributed significantly to the potential for serious spills in the last ten years. The PSA has also closely followed up the industry through audit activities, investigations, sharing experience, seminars, meetings and participation in standardisation work and industry projects. In connection with damage and leaks, the industry has taken responsibility and initiated investigations and in-depth studies, established own projects to look at solutions, shut down facilities as needed, and has worked actively on developing standards and norms.

Leaks in and damage to flexible risers are an unsolved problem area which will require continued focus in coming years. We can see that considerable resources are dedicated to solving problems that arise with incidents, but this could come at the expense of more long-term tasks and improvement measures. It can also lead to an insufficient focus on converting own and relevant other experiences in the industry into broad, up-to-date knowledge in the respective organisations.

Contact information:
Lin Silje Nilsen

Senior engineer, HSE management
E-mail: lin.nilsen@ptil.no