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Spotlight on life on the seabed

July 6, 2004, 14:00 CEST

New methods have been adopted to register life on the seabed in connection with the Ormen Lange development. A remote-controlled vehicle with camera was used to obtain a much fuller picture than ordinary seabed samples would have done.

Extensive surveys have been conducted for several years in advance of the Ormen Lange gas field development, for which Hydro is development-phase operator.

The surveys included the registration of coral reefs along pipeline routes, and in the area where templates will be positioned.

The surveys have revealed the existence of cold-water corals (Lophelia), especially on Egga and close to land, particularly in Bjørnsundet on the route into Nyhamna.

Lophelia is only found at depths of down to 500 to 600 metres because the water is too cold at greater depths. The temperature at the bottom of the Ormen Lange field falls to -1 o C.

Important contribution
"These investigations have made a considerable contribution to registering the coral reefs on the mid-Norwegian continental shelf, and our data has been entered into the Institute of Marine Research's complete survey," says Jon Rytter Hasle, head of HES in Exploration, Hydro Oil & Energy.

"We are laying the pipelines outside the corals," he adds.

"The baseline survey of the field embraces the area where there is a possibility of sedimentation from the cuttings and drilling mud from future production drilling. It will determine the baseline for monitoring the possible impact of future drilling discharges. The area we have investigated is roughly 10 km from north to south and 4 km from east to west."

Elsewhere on the shelf, these surveys consist only of dredging up seabed samples, identifying species and counting the individual items of seabed fauna retrieved.

"The bottom of the North Sea is so flat and even that this is a good method, even though we know that some areas, Gullfaks for example, contain so much sedimentary stone that it can be difficult to obtain samples. Other areas, such as the southern part of the North Sea, are subject to erosion, which means that cuttings and drilling mud will be moved about on the seabed over time."

More complicated
Conditions on Ormen Lange are made much more complicated because of the trench on the Storegga slide. The seabed consists of "basins" of fine clay, lying between ridges that have largely been formed by enormous, hard blocks of clay.

The seabed fauna varies tremendously between these areas, from soft-bottom fauna that is mostly found embedded in the sediment (brushwork, mussels, crayfish) to typically hard-bottom species that are found on top of the sediment (snakestars, sea lilies, sea anemones, sea feathers, crinoids).

"We therefore used a remote-controlled vehicle (ROV) equipped with a camera to look at the creatures we did manage to obtain by dredging. This gave us a much more complete picture than the seabed samples alone would have given us. This is partly because these larger creatures are so spread about that there is little chance of finding them when dredging."

The baseline survey will be followed by a monitoring investigation during the first year after drilling has started, and every third year thereafter.

"The survey will nevertheless have little impact on our drilling and discharge routines. We knew in advance that there were no major coral reefs in the immediate vicinity. Had there been, we would have faced a completely different of drilling challenges. The measures we adopt are the same as for other new developments on the shelf, and involve phasing out harmful chemicals and avoiding environmental damage."

Improvements since 1993
The biggest change took place back in 1993, when discharges of oil-based drilling mud were banned after extensive, unacceptable changes to the seabed fauna on Statfjord were registered as a result of the discharges.

No impact on seabed fauna has been registered more than 250 metres away following the current discharges of water-based drilling mud. Impact has been registered only 50 to 100 metres from the point of discharge.

"This extended baseline survey is in line with Hydro's biodiversity policy. We conduct the most thorough investigation possible before we going in, and obtain a basis for the further monitoring of biodiversity. The baseline survey on Ormen Lange will bring us new knowledge of the deep water fauna on the mid-Norwegian continental shelf," maintains Jon Rytter Hasle.