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Plugging a permanent solution

A new approach by the PSA recently found that the NCS held no less than 193 temporarily abandoned wells – some in a very poor condition. After pressure was brought to bear, the 2012 position looks much better.

This article was published in the magazine "Safety - status and signals 2011-2012"

Wells no longer in use have been a safety issue for the PSA over many years. A number have remained untouched for three or four decades – the oldest since 1970. Most are never going to be reused, but for a variety of reasons the companies responsible have not given priority to plugging them permanently.

“We’ve maintained an overview of abandoned wells for a number of years,” reports Monica Ovesen, discipline manager for drilling and well technology at the PSA.

“We regularly ask the industry what they plan to do with them. These wells are an important aspect of the safety picture, particularly with regard to polluting discharges.”

The PSA believed at the beginning of 2011 that about 40 temporarily abandoned wells were to be found on the NCS, but then decided to tackle the issue in more depth.

“A project was initiated to analyse each well,” Ms Ovesen explains.

“The question we put to the companies was formulated in a rather different way. “We asked for an overview of all wells which were neither active (as producer or injector) nor permanently plugged, and of their condition. The answers we got proved a surprise.”

It turned out that the number of such wells on the NCS was almost five times larger than earlier statistics had shown, Ms Ovesen says.

“When we reviewed the data submitted together with consultants from Sintef and Wellbarrier, we concluded that 62 per cent of the wells fell into the “green” category.

“This means they have double barriers which are intact. A further 29 per cent were categorised as “yellow” – acceptably safe under specified conditions.

“More worrying was that about one per cent fell into the red category and eight per cent were classed as orange. Both are unacceptable in safety terms – with red the worst of all.

”As mentioned above, the figures also showed that a number of the wells had been temporarily abandoned for a very long time. This is not what the PSA understands by “temporary”.

“Concerns over these wells relate primarily to the threat of uncontrolled leaks of oil and gas,” says Ms Ovesen. “Immediate action was required.”

Completed last autumn, the project report showed that a total of eight operators were responsible for the 193 temporarily abandoned wells.

“We went to these companies and requested binding plans for plugging the wells – with priority given to the red and orange categories,” Ms Ovesen reports.

“A couple more rounds of discussion proved necessary before we were satisfied with feedback from the companies. By the New Year, though, we decided that the industry had risen to the

All the wells in the most serious categories are now either plugged or covered by a scheduled plan to do so. And work has been initiated to ensure the integrity of the remaining wells.

“Taken together, this will mean a continuous improvement in the position during 2012,” says Ms Ovesen. “We’re now satisfied with the way the industry is tackling the position, but will be following up implementation during the coming year.”

She says it is difficult to predict how long it will take before all 193 wells have been permanently plugged and abandoned.

“The most important consideration for us now is to ensure that greater attention is paid to temporarily abandoned wells, and that red and orange ones are eliminated entirely.

“However, permanent plugging is a matter of getting things to fall into place. We must also take account of the operators’ rig capacity.”

The experience now acquired in this area has prompted the PSA to assess a change in the regulations.

“A regulatory requirement could be necessary to avoid ending up with a similar accumulation of temporarily abandoned wells in a few years’ time,” Ms Ovesen says.