Stopping the leak
First attempts
Alongside response to the consequences of the spill at the surface, response was also organised to tackle the source of the problem. For several days, four underwater robots attempted to seal the well by activating the blowout preventer which should have been triggered automatically. On 5 May 2010, BP announced that they had succeeded in plugging the smallest of three leaks by fitting a valve using an ROV to shut off the flow.
Recovery from the well
Plugging the leak
BP then attempted to plug the leak with a containment chamber. Two metal domes were specially constructed in Louisiana. One of these containment chambers was taken out to sea on the evening of 5 May 2010 towards the leaking well by the drillship Discoverer Enterprise. Onsite on 6 May, it was lowered to the ocean floor to cap the main leak at a depth of 1,500 m and funnel 80% of the leaking oil to the surface. The Discoverer Enterprise can treat 2,400 m3 of oil a day and has a storage capacity of over 22,000 m3. A barge with a similar capacity was also sent onsite.
On 8 May, attempts to cap the well aborted because a large volume of methane hydrate crystals accumulated inside the containment chamber, preventing the pollutant from being pumped to the surface. The chamber was removed from the seafloor, 500 m from the leak, the following day.
Tool tube in the riser
During the night from 16 to 17 May 2010, a tool tube was successfully inserted into the riser lying on the seafloor and methanol was injected to prevent the formation of methane hydrates. This tube helped to capture some of the oil and gas before it could escape into the sea. The oil was funnelled to the surface, onto the drill ship Discoverer Enterprise where oil, gas and water were separated: the gas was burnt onsite and water discharged into the sea.
New containment chamber
This technique was abandoned on 3 June 2010 to plug the leak with a new containment chamber, smaller than the first. More crude oil was expected to be recovered using this technique than via the tube system. The damaged section of the riser was cut at the wellhead. The containment chamber was connected to the Discoverer Enterprise, the drill ship at the surface. This enabled the majority of the outflow of oil and gas to be trapped, while preventing the formation of methane hydrate crystals due to the injection of methanol.
New riser
A second riser was added to this system on 15 June 2010, connecting the well to the recovery platform Q4000, on which part of the oil and gas was burnt. According to the latest estimations, the Discoverer Entreprise is recovering 2,860 m3 of gas and oil a day and the platform Q4000 between 3,180 and 4,450 m3.
On 22 June 2010, a third FPSO vessel, Helix Producer, was being prepared to be sent on site. The US Government had demanded that BP increase the recovery capacity of the oil leaking from the well. The target was to achieve a daily capacity of between 6,360 and 8,430 m3 by the end of June and 9,540 to 12,720 m3 by the end of July.
Following the arrival of Helix Producer on 30 June 2010, BP's teams began the connection process between the containment chamber and a floating riser.
For safety reasons, recovery and burning operations were suspended on 1st July due to strong waves caused by the cyclone Alex. Operations recommenced on 4 July 2010.
Top Hat 10
On 12 July 2010, a new containment cap baptised Top Hat 10 was placed on the wellhead. This new system was designed to gradually close the well’s valves to completely shut off the leaking oil. Tests are currently being carried out, in particular to measure the pressure once the cap has been fitted. If the pressure is low, this would indicate the appearance of new leaks within the cap system which extends 4 km underground. The results of these tests will determine the viability of this new system.
In late July 2010, the tropical depression Bonnie passed through the Gulf of Mexico. Operations were called off on 23 July, but resumed the following day, only slightly delaying the progress of operations.
Techniques to "kill" the well
Top Kill and Junk Shot
After several fruitless attempts, BP envisaged two other techniques to stop the ceaseless spill of hydrocarbons, directly at the level of the wellhead:
- "top kill" whereby heavy drilling fluids are injected
- "junk shot" which consists of shooting in diverse fragments, such as pieces of tyres.
The "top kill" operation conducted on 27 and 28 May 2010 upon which many hopes were placed, failed because the outgoing flow of hydrocarbons was far too powerful.
Static Kill and Bottom Kill
On 2 August 2010, the “static kill” operation began. It aimed to pump drilling mud and cement into the main well (a similar technique to “top kill”). On 5 August, the US authorities and BP announced that the “static kill” operation had been a success. A second technique, dubbed “bottom kill”, will next be implemented. It will consist of pumping mud and cement, but this time via the relief wells, so as to definitively seal the well.
Drilling of relief wells
Two platforms, named Development Drill III and Development Drill II, arrived onsite respectively on 3 May and 14 May 2010 to drill two relief wells intended to join the main well, to inject a filler to definitively kill the well. An electric signal is regularly sent into each relief well to determine the remaining distance to be drilled before reaching the main well.
On 9 August 2010, the platform Development Drill III drilled a well some 5,458 m into the ocean floor and Development Drill II, a well of around 4,865 m.
On 4 September 2010, the faulty blow-out preventer (BOP) was replaced. On 17 September, the relief well drilled by Development Drill III intercepted the leaking well. On 19 September, the well was definitively plugged by pumping cement into it.