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28 May - Sampling the bottom of the North Sea

RRS Ernest Shackleton Diary

Position @ 1200 CET: 60° 34' North. 3° 39'.4 East, in the vicinity of the Troll Alpha Platform,  vessel in DP mode,  bottom sampling.
Activity: v/l in DP mode,  bottom sampling.
Conditions: Wind WxS x 6kts,  Barometer 1008 mb steady,  Air Temperature 11.4 ° C, Sea Temperature 9.9 ° C,  dense fog throughout,  slight seas, low ground swell.

The past week has seen RRS Ernest Shackleton moving around the Oseberg and Troll Fields conducting bottom sample surveys to monitor the environmental impact of the oil and gas industry on the surrounding area. The article below explains the reasons behind this work.

The simple sample grab. Click to enlarge Getting at the sample in the grab.  Click to enlarge

The simple sample grap and getting at the contents of the grab. Click on images to enlarge.

The work is, in many respects, low tech. Last year RRS Ernest Shackleton had onboard two Remote Operated Vehicles (ROV's) and all the associated equipment and personnel to operate and maintain them, along with very sophisticated tracking equipment. For the work we are doing at the moment, the 'hardware' is a very simple sample grab, which is dropped to the sea-bed (at depths ranging from 100 m to 355 m) on a 6 mm wire, using the ship's small ROV crane. Once the grab is sitting on the seabed, one of the scientific team sharply pulls on the wire and this operates a spring release which causes the grab to close, and in so doing collects a sample of the mud or clay on the seabed. The grab is then raised to the surface and brought onboard. Two small lids allow access to the contents.

Once onboard one of the three scientists on shift then gets the lovely job of syphoning the water out of the grab, using nothing more than a hose pipe and a quick suck. Needless to say there are often times when a mouthfull of saltwater is taken and a steady supply of bottled water is available for removing the taste from the mouth.

The sampling work is due to be completed early next week and when we have finished we will have visited 121 different sites and the grab will have been deployed 1003 times!

The Troll Alpha Platform - The worlds biggest concrete platform

The Troll A platform is situated 80 km northwest of Bergen, Norway. It will produce gas for more than 70 years. It is placed on the sea bottom with big concrete cells and a concrete skirt penetrating the sediment. From the bottom of the skirt to the tip of the flare it is 472 metres. It weighs 650,000 tonnes, or two times the weight of the Norwegian population (4.4 million people).

During the laying of the concrete, 250 million cubic metres of concrete was used. The iron used in the concrete is the equivalent to 15 Eiffel Towers!

The Troll field is the world's greatest gas field, and the biggest offshore gas field. There are 1266 billions cubic metres of gas in the reservoir. The platform produces enough for the Norwegian total annual consumption of energy in 3 seconds! The gas is exported to Europe through pipelines via Kaarsto in Norway.

R.R.S. Ernest Shackleton and Environmental survey 2001 at Oseberg, Brage, Troll fields - Norwegian Continental Shelf.

Norsk Hydro logo From May 14 and to the end of May RRS Ernest Shackleton is used in an envirnmental monitoring survey on the Norwegian Continental Shelf. The ship is hired by Norsk Hydro Exploration & Production, a major oil company in Norway.

Western Norway coastline. Click to enlarge The picture shows the coastline of western part of Norway and the fields are located 50-150 km west of Bergen.
The Norwegian shelf is divided into regions covering the shelf from Ekofisk to the Barent Sea. In each region the operating companies cooperate with regard to the environmental monitoring programmes. This survey includes region III - Oseberg, Brage and Troll with the fields:

  • Oseberg Fieldcentre
  • OsebergC
  • Oseberg East
  • Oseberg South
  • Brage
  • Troll B (area)
  • Troll C (area)

Why monitoring surveys?
The Norwegian State Pollution Control Authority submits discharge permits to the operating companies. These permits demand that the operating companies perform environmental monitoring surveys to give a status of pollution on the sea bottom. Each installation is monitored every third year after a baseline study before drilling starts. The monitoring programme is described in a guideline submitted by the Norwegian Pollution Control Authority - Environmental monitoring in the vicinity of offshore installation on the Norwegian continental shelf.

What is done?
Sampling stations. Click to enlarge The sampling stations are located in an axes cross with the centre of the platform as a reference point. In the Troll area the stations are located around subsea installations. The stations are located at 250 m, 500 m, 1000 m, and 2000 m and a reference station approx 10,000 m upstream. Eight samples (five biology and three chemistry) samples are taken using a special designed grab. At the reference station fifteen samples are taken (ten biology and five chemistry). There are also some regional stations (outside primary influenced area) to be sampled.

The material is conserved and frozen and taken to shore for analysis. Statistical analysis are performed, and a report is submitted to the Norwegian State Pollution Control Authority by 1 April 2002.

There are six scientists working six hours shift (three persons per shift) and two surveyors (who plot the exact location of the sample sites to be used and this data is transferred to the Bridge for navigation) during the day and night. The scientists are from Akvaplan-niva situated in Tromsø, Northern Norway. Akvaplan-niva, one of northern Europe's largest independent companies providing environmental and aquaculture consultancy, is one of four accredited institutions performing such survey work in Norway.

The operating companies have presented a status report on the environment of the Norwegian continental shelf 1996-1998 based on the regional concept of environmental monitoring. You may download this report from the Oil Industry Association of Norway.

The week ahead should see the vessel returning to Haugesund briefly to demobilise the Norsk Hydro personnel and equipment followed by a quick passage to Aberdeen, arriving on Thursday morning, to mobilise three ROV's and associated equipment/personnel.

Mike Gloistein

Weekly diary entries

Akvaplan-niva Oil Industry Association of Norway Norsk Hydro Exploration & Production