The oil leaking from the well is a light crude oil. The ADIOS model, designed to predict the behaviour of oil at sea, indicates that when spilt in the environment, 35% of this oil will evaporate, 10 to 15% will be diluted and the remaining 50% can form an emulsion containing up to 90% water.
Although it remains highly viscous, the recovered oil can be pumped. However, this requires specialised equipment specific to this type of fluid, such as appropriate pumps and a water ring injection system for pipes when the oil is not heated.
By 23 April 2010, the oil spill had already formed a surface slick 1.6 km wide by 8 km long. 32 boats and 5 aircraft were mobilised to spread dispersants and deploy skimmers. In spite of this, an aerial survey on 25 April reported sheen spreading over a surface area of 32 km², containing emulsified crude oil. Two days later, the edge of this slick was a mere 37 km from the coast of Louisiana.
On 28 April 2010, the wind changed direction and pushed the slicks towards the coast of Louisiana, a particularly ecologically and economically sensitive area. On 29, the first patches reached the nearby marshes at the mouth of the Mississippi. On 1st May, the slick covered an estimated 1,500 km², the equivalent of a large city such as London.
The oil slicks moved around at sea, pushed by the wind and currents. In late May/early June 2010, slicks located in the south were pulled into the Loop Current, generating concern that the pollution may move out of the Gulf of Mexico. However, the alert was short-lived. On the shoreline, the pollution extends, to varying degrees, from the very east of Texas to the west coast of Florida.
The role of natural elements
Eddies formed by local currents, and in particular by the Loop Current, play an important role in preventing widespread expansion of the oil. These eddies trap the oil in their centre where it naturally weathers, fragments and breaks down. This has prevented the arrival of major quantities of oil on the western coast of Florida. The only area where currents have caused trouble is in the partially closed Barataria Bay, where certain sites have been heavily hit.