In the aftermath of the Brent Spar fiasco, the environmental issues of decommissioning large structures in the North Sea became the major topic of concern and debate. But this is just one of the now-recognized five key factors. The other four are technical feasibility of the proposed plan; economics impact; public concern; and the potential impact on human health and safety.
It is this latter factor which is now considered to be a somewhat gray area. In the UK there are two check points: the operator must submit a decommissioning safety case to the Health & Safety Executive which demonstrates how the safety risks involved will be reduced to as low a level as is practicable.
This will require major input from contractors. The application for approval of the whole project to the Department of Trade and Industry - offering the Best Practicable Environmental Option - must contain a detailed analysis of the health and safety factors.
The HSE, incidentally, is not responsible for safety when structures or topsides are in transit to shore. This falls within the remit of the Department of Transport.
The industry is now being more open about the potential hazards. A joint UKOOA/E&P Forum discussion paper, aimed at the public in general, says: "Decommissioning is a complex and potentially risky operation.
"Dismantling large structures brings engineering hazards which must be considered carefully. The safety of personnel, such as mechanics, welders, riggers, electricians and divers, is of paramount importance. Any decommissioning option must seek to minimize the hazards of operations such as underwater cutting and cleaning of vessels."
Salim Al-Hassani of the University of Manchester Institute of Science and Technology is one of the recognized gurus on the application of advanced technology transfer to offshore decommissioning from the aerospace, automotive, nuclear and defense industries. He has worked on a number of plans as well as leading innovative research into explosives.
He points out: "There is enormous experience gained in the Gulf of Mexico but, unfortunately, the technology remains irrelevant to the large scale problems we have in the North Sea."
North Sea jackets, for instance, can be up to 10 times heavier than any jacket removed to date. Topsides weigh over 20,000 tons and large jackets are located in up to 600 ft of water. To date, no large installations have been abandoned.
The largest jacket removed in the Gulf weighed just 5,200 tons. The first two large installations to be removed in the North Sea are likely to be Amoco's NW Hutton, with a jacket of 15,557t, 5,067t of piles and 21,000t of topsides; and Unocal's Heather platform, where the jacket weighs 23,000 tons and the topsides 22,000 tons.
Al-Hassani claims that not enough is known about, for instance, explosive cutting, structural response to toppling options, removal of concrete and the effects on people. Hence the requirement for further research.
The HSE believes that industry will probably be able to conduct the removal operations safely. But it recently commissioned a study to identify any research needed for this to happen. The study pointed out that: "While some operations would be similar to construction or maintenance operations, in many respects abandonment is special and subject to unknowns.
"Conflicting opinion needs to be resolved in several areas including preferences for piece small removal using a large offshore workforce versus piece large removal using large offshore cranes."
The study concluded that additional research into safety aspects is needed because of the perceived risks. Special recommendations include a further study of safety-related incidents during platform abandonment. There have been several major accidents, including fatalities during platform removal in the US.
"There is widespread concern about the risk and consequences of misfires during detonation of explosives, but the practicitioners claim high reliability. This claim should be validated."
Other areas to examine include the integrity of structures for lifting if they were designed to be barge launched. Also, encouragement should be given to the development of underwater remote handling systems to minimize the use of divers in potentially hazardous situations.
In Norway, the only structures so far removed are small. Operators have to submit a cessation of production plan to the Norwegian Petroleum Directorate and to the Ministry. The new government White Paper on decommissioning is due to be discussed in the Storting early this summer.
NPD's Olav Fjellsa says this will not deal with safety as a specific matter. But it is important when the operator submits the plan that safety measures are thoroughly explained.
Norwegian policy is that a decision on each case for decommissioning will be taken in a socio-economic context, where abandonment costs are weighed against the technical, environmental and safety aspects.
Copyright 1996 Offshore. All Rights Reserved.