Facts and fiction on seismic surveys

Seismic surveys are yesterday’s technology

The NPD regards both two- and three-dimensional seismic surveying as necessary for mapping the sub-surface. Survey methods are continuously advancing.

Various technologies developed in recent years can supplement seismic surveys rather than supplant them. A case in point is electromagnetism (EM). The NPD also regards maintaining pressure for technological progress as one of its duties.

 

The oil industry takes no account of fishing interests

Seismic data gathering on the Norwegian continental shelf is governed by the petroleum regulations, and must take second place to fishing activities.

Licensees must submit plans for each survey to the NPD, which consults with the Directorate of Fisheries, the Norwegian Institute of Marine Research (HI) and the defence forces.

Should the fisheries directorate and the HI advise against a survey, this recommendation will usually be accepted. In those cases where it is not, the NPD specifies in its consent that the work must be terminated if fishing activity is under way or about to start in the area. The NPD must also be contacted in such circumstances.

All seismic survey vessels must carry at least one fishery expert, whose job is to help to prevent conflicts arising with fishing activities.

 

Fishery experts carry no weight on seismic ships

From time to time, the NPD is notified that no attention has been paid to the fishery expert. These cases are investigated, and the companies informed that this is a breach of the regulations.

The agency is very concerned about the expert’s status, and the regulations will be amended next year to clarify that this person must have a free and independent position on board.

A requirement will also be introduced that the expert must complete a special course, and the NPD is due to start offering such training next spring.

 

Seismic waves are generated by air guns

The seismic source – as the surveyors call it – is a container about the same size as a vacuum flask.

However, a large number of these – usually 16-24 – are discharged simultaneously every 10 seconds or after a specified distance has been covered.

Dynamite was used to shoot seismic in the early 1960s, but progress has fortunately been made here in both safety and technological terms.

 

3D seismic can be compared with carpet bombing

The number of seismic signal sources is about the same with 2D and 3D surveying. However, a 2D survey uses a single hydrophone streamer to collect data, and the lines can be one-three kilometres apart. The 3D technique involves towing six to 12 streamers, with tighter lines. Each vessel line can be as little as 300 metres apart.

 

Seismic shooting is very noisy and makes vessels vibrate

When the seismic sources are shooting, all that can be heard on the vessel is a low rumbling. People do not have to wear ear protectors. Shooting in deep water is barely noticeable on board, but vibration might be felt by crew in waters shallower than 50 metres.

 

Seismic shooting kills larvae and fry

The HI, Norway’s leading scientific body in this field, has found that seismic surveys kill some fish fry very close to the source. But the quantities involved are so small that this has no effect on the level of stocks. Moreover, no seismic shooting is permitted when fish are spawning over large areas.

 

Far too little research has been done on fish and seismic surveys

A great deal of research has been conducted in this area. While this has focused elsewhere mainly on marine mammals, Norwegian attention has largely been on fish.

Such work has been collated in a report produced by Det Norske Veritas on behalf of the Norwegian Oil Industry Association (OLF).

The NPD wants to encourage more research on the subject. Plans include a trail research project on 3D seismic surveys, to be commissioned by the agency in the Nordland VII and Troms II areas off northern Norway next summer.

 

The seismic survey business is full of cowboys

This claim has been heard by the NPD, but cannot be squared with what it knows about the industry. Seismic survey companies generally comply with the regulations and established procedures.

In most cases where surveyors are alleged to have ridden roughshod over fishing interests, it has proved impossible to establish any illegal activities. This is often a case of one person’s word against another’s.

The NPD views the seismic industry as a responsible business. Some 90 per cent of its data are gathered from production licences for oil companies, which have overall interest in ensuring that their sub-contractors behave properly and predictably.


Topics: Seismic

15.12.2008