Environmental surveys around North Sea platforms
Anne Berit Bjørken
Every year, studies of the seabed around North Sea oil platforms are carried out on behalf of the oil companies. The aim is to monitor contamination from drilling oil wells and any effects on the benthic fauna.
Frøydis Oreld (left) and Tone Øfsti at SINTEF Industrial Chemistry with equipment used to collect samples of the seabed around North Sea oil platforms.
"The idea of these environmental studies is to look at changes in levels of pollution, the size of the area affected around the platform and the effects of discharges on animal life," says Nina Gjøs, a SINTEF Industrial Chemistry scientist.
Studies carried out by SINTEF have demonstrated an obvious connection between discharges of drillcuttings and biological disturbances. There are also clear signs that animal life returns to normal when emissions stop, although this may take some time.
On January 1 1993, the regulations dealing with discharge of drillcuttings were tightened up. No more than 1% oil may be present in cuttings. As a result, most cuttings are no longer released into the sea, but are brought ashore.
"In order to determine the conditions in the North Sea today, a total assessment of all the studies that have ever been done, is carried out by the State Pollution Control Authority," says Gjøs.
IKU Petroleum Research and SINTEF Industrial Chemistry have been key actors in monitoring seabed conditions near platforms since 1981. Other institutes in Norway and the UK have also participated.
Drillcuttings
During drilling operations, drilling fluids are used to lubricate the drill-bit and keep it cool. The drilling liquid, or "mud" as it is also known, also brings up sludge and cuttings from the drilling process to the surface. To date, mineral oil and barium sulphate have been the most important components of drilling fluid, and the seabed around drilling platforms thus becomes contaminated by oil when the used mud is discharged into the sea. The chemical analyses include total mineral oil as well as selected components and metals. The biological analyses deal with animal life in the sediments, and they record which species disappear and which flourish under these conditions. Generally speaking, in a contaminated area we find few species, with particular "pollution species" dominating."The oil companies take the harmful effects of oily cuttings on animal life very seriously. They are currently concentrating on identifying chemicals capable of replacing the oil. Alternative drilling fluids have been tested in a few wells in the course of the past few years, and the new chemicals are also being monitored," says Gjøs.