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4 seismic surveys in one

A challenging subsurface in the Barents Sea has sparked a sea of creativity. For the first time ever, we will be combining TopSeis seismic technology with 1,000 special-made wireless receivers on the seabed.

“In simple terms, we’re using nearly all the tools in our seismic toolbox at the same time,” says Per Eivind Dhelie.

Dhelie is a senior geophysicist in Lundin Energy Norway, and heads up the work to collect seismic data from the Barents Sea. Two different types of signal sources will be used for this collection, and two different methods of registering the signal reflections. That will result in four sets of data that can be put together to achieve an optimal depiction of the subsurface in the North Cape Basin.

The basis for the collection of seismic data is an expanded version of the TopSeis technology. This method was developed based on an idea from Lundin’s exploration department, and involves using two vessels in tandem where the first vessel tows the streamers, while boat number two tows the signal source. More and better data can be collected by placing the signal source over the cables instead of in front of them.

“When using TopSeis, we’ve previously used 3 or 4 signal sources. Now we’re increasing this to 6 sources while simultaneously setting a record in width, with 437.5 metres,” says Per Eivind Dhelie.
“And we’re also towing an extra signal source behind the boat in the front. This source will run relatively deep in the sea, and emit low-frequency signals.”

1,000 nodes tossed over board
The last and perhaps most unique part of this seismic collection endeavour is the use of 1,000 specially-constructed receivers, or nodes, which will lie on the seabed collecting data.

“The subsurface in the North Cape Basin in the Barents Sea is full of salt that has pressed its way up through the sediments, creating salt pillars. In some cases also as overhangs. This results in a very odd geometry, and significant local velocity differences for the signals that pass by,” explains Per Eivind Dhelie.

“That’s when we need an accurate velocity model. And this is where the nodes enter the picture,” says Dhelie.

Laying nodes on the seabed is not a new thing. But they would normally be attached to long lines, or placed using an ROV.

A ‘pinger’ is attached to the wireless receiver node before it’s thrown over board.

“We’ve found a much simpler and cheaper solution where we fasten a ‘pinger’ to each of the nodes, and quite simply toss them over board,” Dhelie explains. “Then we use a ‘pinger boat’ to locate them on the seabed.”

Both nodes and pingers are wireless and run on batteries, which means they can be laid on the seabed, ready for action when the seismic vessels come along. They are retrieved again afterwards so the registered data can be recorded. Lundin’s nodes are special-built by the Geospace Technologies company in Houston. They feature large surfaces on the sides, which allows them to be picked up by an underwater vessel with suction cups. This will be considerably easier and faster than using an advanced ROV arm.

Data collected by the nodes will be used to prepare extremely accurate velocity models with the aid of data algorithms.

Starting this summer
Lundin has always been at the forefront when it comes to using new seismic technology, and we have contributed to developing several new technological solutions in the field.

“Of course it would have been nice if we had a ‘simpler’ subsurface in the North Cape Basin. But since our starting point is a bit challenging, I must say it’s a lot of fun to work in a company that dares to look for new solutions. We’ve tested all the elements we’re going to use now, but we are naturally excited to see how good the images will actually be, once we put all the data together,” says Per Eivind Dhelie.

The seismic collection operation in the North Cape Basin in the Barents Sea will take place this summer. Lundin Energy Norway recently awarded a contract for the seismic survey to PGS.