Abstract
The present study was made on request from Talisman and includes simulations of oil drift and spreading of condensate from possible major blowouts at the Rev field. The discharge rates of oil and gas for possible blowout situations during drilling at the Rev field have been computed by Well Flow Dynamics. The maximum condensate rate of 4670 m3/day was found for a blowout from the entire reservoir. The second largest (1960 m3/day) was found for a blowout from the top reservoir. The gas-to-oil ratio (GOR) was assumed to be 2540 Sm3/Sm3 in both cases. The near field simulations were made for these discharge rates. The discharge depth was set according to water depth at the site (87 m). The plume rise time was found to be very short in both cases, i.e. in the order of 10 (entire reservoir) to 20 seconds (top reservoir). Also, due to the large gas-to-oil ratio, the surfacing condensate was found to form very thin surface slicks (20 to 30 microns). Far field simulations were conducted for the largest spill rate with SINTEF’s OSCAR model. The spill duration was chosen as 5 days. The simulation was based on 3-D current fields from hydrodynamic model simulations produced by the Norwegian Meteorological Institute. The simulation started May 1 1990, and was continued with wind and current data for the following 10 days. A very small fraction of the condensate was found to remain on the sea surface, while most of the condensate will evaporate or be mixed into the water masses. A mapping of the water volume that was contaminated by condensate (swept volume) showed that dissolved hydrocarbon concentrations above100 ppb may be found up to about 30 km from the spill site. Dissolved hydrocarbon concentrations below this level are not expected to be harmful to sensitive marine organisms (fish egg or larvae).
