Efforts to stem the Deepwater Horizon oil spill were ongoing from the time that the Deepwater Horizon exploded on April 20, 2010 until the well was sealed by a cap on July 15, 2010. Various species of dolphins and other mammals (61 casualties), birds (2,095 casualties), and the endangered sea turtles (467 casualties) have been killed either directly or indirectly by the oil spill. The Deepwater Horizon spill has surpassed in volume the 1989 Exxon Valdez oil spill as the largest ever to originate in U.S.-controlled waters; it is comparable to the 1979 Ixtoc I oil spill in total volume released (Ixtoc discharged to ; as of mid-July 2010, Deepwater Horizon has spilled to ).
Much of the oil is so far down in the Gulf that only nature, including microbes, will be able to remove it using a process called bioremediation. Terry Hazen of the Department of Energy's Lawrence Berkeley National Laboratory said the process could take months or years. But after six weeks of research, he said that microbes could work quickly in water as opposed to colder-temperature waters. The A Whale, which is an oil tanker converted into a giant oil skimmer owned by the Taiwan Marine Transport Co (TMT), could do little because of BP's use of chemical dispersants, the company said. Robert Bea of The University of California, who worked on the Ixtoc spill and the 1969 Santa Barbara oil spill, said the old methods would be the best ones. Dispersants, he said, did not work except in keeping beaches clean, and they hurt the environment.
Non-explosive closure attempts
Short Term Efforts
The first attempts to stop the oil spill were to use remotely operated underwater vehicles to close the blowout preventer valves on the well head; however, all these attempts failed. The second technique, placing a containment dome (which had worked on leaks in shallower water) over the largest leak and piping the oil to a storage vessel on the surface, failed when gas leaking from the pipe combined with cold water formed methane hydrate crystals that blocked the opening at the top of the dome.
On May 14, engineers began the process of positioning a wide riser insertion tube into the wide burst pipe. There was a stopper-like washer around the tube that plugs the end of the riser and diverts the flow into the insertion tube. The collected gas was flared and oil stored on the board of drillship Discoverer Enterprise. of oil was collected before removal of the tube.
On May 26, BP tried to close the well using a technique called "top kill", which also failed. This process involved pumping heavy drilling fluids through two lines into the blowout preventer to restrict the flow of oil before sealing it permanently with cement.
On May 29, BP moved to the Lower Marine Riser Package (LMRP) Cap Containment System by removing the damaged riser from the top of the blowout preventer and covering the pipe by the cap which connects it to a riser. The cap was attached on June 3, and the system began to capture the leaking oil. On June 6, the CEO of BP Tony Hayward, stated that the amount captured was "probably the vast majority of the oil." However, Ira Leifer, a member of the Flow Rate Technical Group (FRTG), claimed that more oil was escaping than before the riser was cut and the cap containment system was placed.
On June 16, a second containment system connected directly to the blowout preventer became operational carrying oil and gas through a subsea manifold to the Q4000 service vessel with a processing capacity for about of oil per day. Oil and gas are both burned on Q4000 in a clean-burning system.
As Discoverer Enterprise'''s processing capacity was insufficient, drillship Discoverer Clear Leader and the floating production, storage and offloading (FPSO) vessel Helix Producer 1 were added, offloading oil with tankers Evi Knutsen, and Juanita. Each tanker has a total capacity of . In addition, FPSO Seillean, and well testing vessel Toisa Pisces would process oil. They are offloaded by shuttle tanker Loch Rannoch.
On July 5, BP announced that its one-day oil recovery effort accounted for of oil, and the flaring off of of natural gas. The total oil collection to date for the spill was estimated at . The government's estimates suggested the cap and other equipment were capturing less than half of the oil leaking from the sea floor as of late June.