LOMROG 2007, Field Report no. 3
Oden, August 21, 2007, Seismic data acquisition in the Arctic Ocean
The Pobedy comes alongside close to the Oden helping us to progress in the iceEnlarge
Air gun and cables on ice floeEnlarge
Received from Trine Dahl-Jensen, GEUS
Edited by Jane Holst and Torsten Hoelstad, GEUS
The new seismic equipment specially designed for the Continental Shelf Project has come through its "baptism of ice" almost unscathed. From very early morning on 19 August and for about to days, the main activity on board the Oden was collection of seismic data. Everything from streamer, air gun, compressors to registration container has been developed in close cooperation with University of Aarhus, specially designed to function in the pack ice. And it did work just as intended.
To keep the equipment free of the ice, there is only one cable (orange) from the ship into the water holding the streamer, compressor air as well as cables for the air gun. The strong 'head' descends to a water depth of 20 to 30 m. Both air gun and streamer are hanging from the 'head'. As long as everything stays at that depth, it is under the ice and remains relatively safe. Even when the Oden is stuck and tries to push through a pressure ridge at full power, the streamer stays below.
We were working in very dense pack ice - 10/10 multiyear ice - with many thick pressure ridges. Fortunately, the Russian nuclear ice-breaker 50 Let Pobedy helps us, otherwise it would not amount to many seismic measurements. We are in an area where very few - if any - surface ships have been before. The Oden normally progresses by reversing, trying to gain as much speed as possible to ram through the pressure ridges, but with the seismic equipment in use astern this is not possible. This is when the Pobedy takes action. Leaving its front position where it usually makes a channel, it turns around and comes alongside the Oden to break the ice and enable the Oden to push the ice away and progress. The most effective result is obtained if the Pobedy comes close to the Oden - very close!
It sometimes happens that pieces of ice get stuck under our orange cable. Usually the cable slides off again shortly after, but a few times the entire equipment is drawn over an ice floe. This always creates intense activity to reduce the speed of the ship and check to see if the streamer is drawn over the floe without being damaged and if it descends into the safety of the depth again. Just after midnight on 21 August, we lost most of our streamer, while it was drawn over an ice floe. Luckily, we have brought spare parts and could continue along the next planned line.
We have acquired approx. 130 km of seismic data during the course of two days in an area where seismic data have never been acquired before. So we are pleased with the result.
The Oden during data acquisition. The channel behind the Oden closes very fast due to the drift of the iceEnlarge
Lars-Georg Rödel and Thomas Vangkilde Pedersen (both GEUS) busy getting the equipment into the water. They are standing on the open quarter deck equipped with the required safety line and inflatable life west as well as hard hat and safety bootsEnlarge
The seismic equipment being hoisted from the water. At the top the orange cable from the ship down to the 'head', from which the air gun is hanging and the streamer continues astern from the ship. Enlarge