|Oil Spill Challenge Rehearsal|
The South Arne platform in Danish waters has had a major disaster (simulation!). Ecoterrorists have taken control of the rig and are diverting the production into the sea. Can you find out where the oil goes and what impact it has on human activity and the ecosystem?
The response team used the EU's Copernicus marine service forecasting system for current forecasts, the satellite communication company GlobalMarineNet for wind forecasts and NOAA's GNOME system for tracking the spill. The direction and magnitude of currents and winds were available at six hour intervals for a five day period. GNOME interpolates with a time step of 15 minutes. GNOME calculates a 'best estimate' where the oil spill is likely to end up and a 'minimum regret' using conservative assumptions that cause it to spread over a much wider area. It includes output as a movie and this was used to visualise the results (black dots in the movie represent the 'best estimate' oil spill trajectory, red dots represent the 'minimum regret', the purple arrows show both wind strength and direction).
The positions of the slick were output every six hours to a geographical information system (ESRI ArcMap), which was used to ascertain whether the trajectory of the spill came near features such as shipping routes, other oil and gas infrastructure, bathing beaches and marine protected areas. This analysis was ready half an hour after completion of the trajectory model.
The impact data
A digital geographical database of the location and nature of bathing beaches and Natura 2000 nature protection sites was obtained from the European Environment Agency Information on the location of oil platforms and shipping lanes was obtained from a previous project (WindSpeed). This is a collated dataset covering the Central and Southern North Sea (Belgium, Denmark, Germany, Netherlands, Norway, United Kingdom).
The images below show the situation after 72 hours, showing position with respect to bathing beaches, NATURA sites and oil platforms (left) and bathing beaches, NATURA sites and shipping density (right).
A recent report on Oil and Gas Production in Denmark (2013), gave a total production volume of 700.000 m3 per year for the South Arne location. This report as well as the Subsea IQ website indicated that the geological strata (Danian and Maastrichtian) were similar to the Ekofisk and Tor fields in Norway. Other websites pointed to similar API gravity and sulphur content so the released oil was considered to be light crude similar to the Ekofisk blend. It was therefore assumed that one day's production, 1918 m3, was being lost into the sea at a constant rate. Light crude was not one of the options offered by the models, so the medium-crude option was chosen.
Results after 24 hours
The calculation could continue for only five days because forecasts of wind and waves were not available beyond then. At this time 55% of the oil would still be floating over an area of 260km2 and the rest evaporated or dispersed. The spill would not have reached land and no Nature 2000 sites or tourist sites were threatened. Whilst it would cover some fishing areas, it would not affect major fishing grounds. However, it would affect a region with heavy ship traffic particularly routes between Denmark and Norway and between Germany and Norway. Assuming that the spill continued beyond one day would have resulted in a larger area coverage.
Results after 72 hours
More detailed analysis in the next 72 hours showed that:
- the slick would almost certainly affect other oil platforms - Cecile, Nini and Nini E and possibly also Valdemar and Tyra fields;
- the spawning of major commercial fish stocks will not be affected because cod and plaice spawn earlier (December-February) and herring later (August-December);
- the Danish Natura 2000 area Jyske Reve/Lillefiserbanker which aims to protect seabed reefs and harbour porpoises could be affected; and
- some tiny amounts could reach the coast of Jutland: north of Thyborøn and near Klitmøller and the the island of Bressay in the Shetlands tourist beaches are unlikely to be affected.
The following graph shows the fate over time of the spilled oil, with an increased total oil amount during the simulated duration of 120 hours (five days). During that time the amount of oil in/on the water increases, as the spill stops, the process of evaporation continues and as a result the amount of oil remaining in/on the water begins to decrease. There is no (appreciable amount of) oil in the simulation that reaches land. The unit of the Y-axis is based on grams of oil as the oil spill trajectory modelling software (GNOME) calculates with that unit. A Million grammes equals a (metric) tonne or 1000 kg.
Accessing the reports on the simulated oil spill
Download the 24h initial assessment report here
Download the 72h refined assessment report here