Deepwater Horizon oil spill also referred to as the bp oil spill, the bp oil disaster

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Volume and extent of oil spill

Main article: Timeline of the Deepwater Horizon oil spill

An oil leak was discovered on the afternoon of 22 April when a large oil slick began to spread at the former rig site.[54] According to the Flow Rate Technical Group, the leak amounted to about 4.9 million barrels (780,000 m3) of oil, exceeding the 1989 Exxon Valdez oil spill as the largest ever to originate in U.S.-controlled waters and the 1979 Ixtoc I oil spill as the largest spill in the Gulf of Mexico.[3][11]

Spill flow rate

In its permit to drill the well, BP estimated the worst case flow at 162,000 barrels per day (25,800 m3/d).[55] Immediately after the explosion, BP and the United States Coast Guard did not estimate any oil leaking from the sunken rig or from the well.[56] On 24 April, Coast Guard Rear Admiral Mary Landry announced that a damaged wellhead was indeed leaking.[57][58] She stated that "the leak was a new discovery but could have begun when the offshore platform sank . . . two days after the initial explosion."[57] Initial estimates by Coast Guard and BP officials, based on remotely operated vehicles as well as the oil slick size, indicated the leak was as much as 1,000 barrels per day (160 m3/d).[57] Outside scientists quickly produced higher estimates, which presaged later increases in official numbers.[59][60][61] Official estimates increased from 1,000 to 5,000 barrels per day (160 to 790 m3/d) on 29 April,[62][63] to 12,000 to 19,000 barrels per day (1,900 to 3,000 m3/d) on 27 May,[64][65][66][67] to 25,000 to 30,000 barrels per day (4,000 to 4,800 m3/d) on 10 June,[68][69][70] and to between 35,000 and 60,000 barrels per day (5,600 and 9,500 m3/d), on 15 June.[71][72] Internal BP documents, released by Congress, estimated the flow could be as much as 100,000 barrels per day (16,000 m3/d), if the blowout preventer and wellhead were removed and if restrictions were incorrectly modeled.[73][74]

Official estimates were provided by the Flow Rate Technical Group—scientists from USCG, National Oceanic and Atmospheric Administration (NOAA), Bureau of Ocean Energy Management, Regulation and Enforcement, U.S. Department of Energy (DOE), and outside academics, led by United States Geological Survey (USGS) director Marcia McNutt.[76][77][78] The later estimates were believed to be more accurate because it was no longer necessary to measure multiple leaks, and because detailed pressure measurements and high-resolution video had become available.[79] According to BP, estimating the oil flow was very difficult as there was no underwater metering at the wellhead and because of the natural gas in the outflow.[62] The company had initially refused to allow scientists to perform more accurate, independent measurements, saying that it was not relevant to the response and that such efforts might distract from efforts to stem the flow.[22] Former Administrator of the Environmental Protection Agency Carol Browner and Congressman Ed Markey (D-MA) both accused BP of having a vested financial interest in downplaying the size of the leak in part due to the fine they will have to pay based on the amount of leaked oil.[80]

The final estimate reported that 53,000 barrels per day (8,400 m3/d) were escaping from the well just before it was capped on 15 July. It is believed that the daily flow rate diminished over time, starting at about 62,000 barrels per day (9,900 m3/d) and decreasing as the reservoir of hydrocarbons feeding the gusher was gradually depleted.[11]

Spill area and thickness

The oil's spread was initially increased by strong southerly winds caused by an impending cold front. By 25 April 2010, the oil spill covered 580 square miles (1,500 km²) and was only 31 miles (50 km) from the ecologically sensitive Chandeleur Islands.[81] An 30 April 2010, estimate placed the total spread of the oil at 3,850 square miles (10,000 km²).[82] The spill quickly approached the Delta National Wildlife Refuge and Breton National Wildlife Refuge.[83] On 19 May 2010, both the National Oceanic and Atmospheric Administration and other scientists monitoring the spill with the European Space Agency Envisat radar satellite stated that oil had reached the Loop Current, which flows clockwise around the Gulf of Mexico towards Florida and then joins the Gulf Stream along the U.S. east coast.[84] On 29 June 2010, the National Oceanic and Atmospheric Administration determined that the oil slick was no longer a threat to the loop current and stopped tracking offshore oil predictions that include the loop currents region. The omission is noted prominently on the ongoing nearshore surface oil forecasts that are posted daily on the National Oceanic and Atmospheric Administration site.[84][85]

On 14 May 2010, the Automated Data Inquiry for Oil Spills model indicated that about 35% of a hypothetical 114,000 barrels (18,100 m3) spill of light Louisiana crude oil released in conditions similar to those found in the Gulf would evaporate, that 50% to 60% of the oil would remain in or on the water, and the rest would be dispersed in the ocean. In the same report, Ed Overton, a Louisiana State University chemist who analyzed the spill for NOAA, said he thought most of the oil was floating within 1 foot (30 cm) of the surface.[86] The New York Times tracked the size of the spill over time using data from National Oceanic and Atmospheric Administration, the US Coast Guard and Skytruth.[87]

The wellhead was capped on 15 July 2010, and by 30 July, the oil appeared to have dissipated more rapidly than expected. Some scientists believe that the rapid dissipation of the surface oil may have been due to a combination of factors that included the natural capacity of the region to break down oil (petroleum normally leaks from the ocean floor by way of thousands of natural seeps and certain bacteria can consume it.); winds from storms appeared to have aided in rapidly dispersing the oil, and the cleanup response by BP and the government helped control surface slicks. As much as 40% of the oil may have simply evaporated at the ocean surface[citation needed], and an unknown amount remains below the surface.[88]

However, many scientists dispute the report's methodology and figures.[89] Scientists said much oil was still underwater and could not be detected.[90] According to the NOAA report released on 4 August 2010, about half of the oil leaked into the Gulf remains on or below the Gulf's surface.[91] Some scientists are calling the NOAA estimates "ludicrous." According to University of South Florida chemical oceanographer David Hollander, while 25% of the oil can be accounted for by burning, skimming, etc., 75% is still unaccounted for.[92] The federal calculations are based on direct measurements for only 430,000 barrels (68,000 m3) of the oil spilled – the oil burned and skimmed. According to Bill Lehr, an author of the NOAA report, the other numbers are "educated scientific guesses," because "it is impossible to measure oil that is dispersed". FSU oceanography professor Ian MacDonald called it "a shaky report" and is unsatisfied with the thoroughness of the presentation and "sweeping assumptions" involved.[93] John Kessler of Texas A&M, who led a National Science Foundation on-site study of the spill, said the report that 75% of the oil is gone is "just not true" and that 50% to 75% of the material that came out of the well remains in the water in a "dissolved or dispersed form".[94] On 16 August 2010, University of Georgia scientists said their analysis of federal estimates show that 80% of the oil the government said was gone from the Gulf of Mexico is still there. The Georgia team said "it is a misinterpretation of data to claim that oil that is dissolved is actually gone".[95]

In a 3 December 2010, statement, BP claimed the government overestimated the size of the spill by between 20% and 50%. A document submitted by BP to the commission, NOAA, and The Justice Department says that "they rely on incomplete or inaccurate information, rest in large part on assumptions that have not been validated, and are subject to far greater uncertainties than have been acknowledged. Representative Edward Markey, a member of the House energy panel that is investigating the spill, said in a statement that BP has done whatever it could to avoid revealing the true flow rate of the spill. "With billions of dollars at stake, it is no surprise that they are now litigating the very numbers which they sought to impede." A BP spokesperson said that BP "fully intends to present its own estimate as soon as the information is available to get the science right."[96]

Oil sightings

Oil began washing up on the beaches of Gulf Islands National Seashore on 1 June 2010.[97] By 4 June 2010, the oil spill had landed on 125 miles (201 km) of Louisiana's coast, had washed up along Mississippi and Alabama barrier islands, and was found for the first time on a Florida barrier island at Pensacola Beach.[98] On 9 June 2010, oil sludge began entering the Intracoastal Waterway through Perdido Pass after floating booms across the opening of the pass failed to stop the oil.[99] On 23 June 2010, oil appeared on Pensacola Beach and in Gulf Islands National Seashore, and officials warned against swimming for 33 miles (53 km) east of the Alabama line.[100][101] On 27 June 2010, tar balls and small areas of oil reached Gulf Park Estates, the first appearance of oil in Mississippi.[102] Early in July 2010, tar balls reached Grand Isle, but 800 volunteers were cleaning them up.[103] On 3 and 4 July 2010, tar balls and other isolated oil residue began washing ashore at beaches in Bolivar and Galveston, though it was believed a ship transported them there, and no further oil was found 5 July.[104] On 5 July 2010, strings of oil were found in the Rigolets in Louisiana, and the next day tar balls reached the shore of Lake Pontchartrain.[104][105]

On 10 September 2010, it was reported that a new wave of oil suddenly coated 16 miles (26 km) of Louisiana coastline and marshes west of the Mississippi River in Plaquemines Parish. The Louisiana Department of Wildlife and Fisheries confirmed the sightings.[106] On 23 October 2010, it was reported that miles-long stretches of weathered oil had been sighted in West Bay, Texas between Southwest Pass, the main shipping channel of the Mississippi River, and Tiger Pass near Venice, Louisiana. The sightings were confirmed by Matthew Hinton of The Times-Picayune.[107]

At the end of October 2010, two research vessels studying the spill's effect on sea life found substantial amounts of oil on the seafloor. Kevin Yeager, a University of Southern Mississippi assistant professor of marine sciences found oil in samples dug up from the seafloor in a 140-mile (230 km) radius around the site of the Macondo well. The oil ranged from light degraded oil to thick raw crude. The sheer abundance of oil and its proximity to the well site, though, makes it "highly likely" that the oil is from the Macondo well. A second research team turned up traces of oil in sediment samples as well as evidence of chemical dispersants in blue crab larvae and long plumes of oxygen-depleted water emanating from the well site 50 miles (80 km) off Louisiana's coast.[108]

In late November, Plaquemine Parish, Louisiana coastal zone director P.J. Hahn reported that more than 32,000 US gallons (120 m3) of oil had been sucked out of nearby marshes in the previous 10 day period. In Barataria Bay, Louisiana, photos and firsthand accounts show oil still reaching high into the marshes, baby crabs and adult shrimp covered by crude and oil slicks on the surface of the water.[25]

Underwater oil plumes

On 15 May 2010, researchers from the National Institute for Undersea Science and Technology,[109] aboard the research vessel RV Pelican, identified oil plumes in the deep waters of the Gulf of Mexico,[110] including one as large as 10 miles (16 km) long, 3 miles (4.8 km) wide and 300 feet (91 m) thick in spots. The shallowest oil plume the group detected was at about 2,300 feet (700 m), while the deepest was near the seafloor at about 4,593 feet (1,400 m).[111] Other researchers from the University of Georgia found that the oil may have occupied multiple layers.[112]

By 27 May 2010, marine scientists from the University of South Florida had discovered a second oil plume, stretching 22 miles (35 km) from the leaking wellhead toward Mobile Bay, Alabama. The oil had dissolved into the water and was no longer visible. Undersea plumes may have been the result of the use of wellhead chemical dispersants.[113]

The National Oceanic and Atmospheric Administration (NOAA) conducted an independent analysis of the water samples provided from the 22–28 May 2010, research mission of the University of South Florida's Weatherbird II vessel. The samples from all undersea plumes were in very low concentrations, less than 0.5 parts per million. NOAA indicated that one of the plumes was unrelated to the BP wellhead leak, while the other plume samples were in concentrations too low or too highly fractionated to determine their origin.[114]

Reporting on a study that ended on 28 June 2010, scientists published conclusive evidence of a deep plume 22 miles (35 km) long linked directly to the Deepwater Horizon well. They reported that it did not appear to be degrading quickly and that it may pose a long-lasting threat for marine life deep in the ocean.[115]

On 23 July 2010, University of South Florida researchers and NOAA released two separate studies confirming subsea plumes of oil resulting from the Deepwater Horizon well.[116]

Researchers from NOAA and Princeton University concluded that the deep plumes of dissolved oil and gas would likely remain confined to the northern Gulf of Mexico and that the peak impact on dissolved oxygen would be delayed (several months) and long lasting (years).[117]

David Valentine of the University of California, Santa Barbara believes that the oil plumes had been diluted in the ocean faster than they had biodegraded, suggesting that the LBNL researchers were overestimating the rate of biodegration.[118] He did not challenge the conclusion that the oil plumes had dispersed.

When scientists initially reported the discovery of undersea oil plumes, BP stated its sampling showed no evidence that oil was massing and spreading in the gulf water column. NOAA chief Jane Lubchenco urged caution, calling the reports "misleading, premature and, in some cases, inaccurate."[119] Researchers from the Universities of South Florida and Southern Mississippi claim the government tried to squelch their findings.[120][121][122] In a report released on 8 June 2010, NOAA stated that one plume was consistent with the oil from the leak, one was not consistent, and that they were unable to determine the origin of two samples.[114]

On 23 June 2010, NOAA released a report which confirmed deepwater oil plumes in the Gulf and that they did originate from BP's well, citing a "preponderance of evidence" gathered from four separate sampling cruises. From the government's report:[123] "The preponderance of evidence based on careful examination of the results from these four different cruises leads us to conclude that DWH-MC252 oil exists in subsurface waters near the well site in addition to the oil observed at the sea surface and that this oil appears to be chemically dispersed. While no chemical "fingerprinting" of samples was conducted to conclusively determine origin, the proximity to the well site and the following analysis support this conclusion".[124]

In October 2010, scientists reported a continuous plume of over 22 miles (35 km) in length at a depth of about 3,600 ft (1,100 m). That plume persisted for several months without substantial degradation.[125]

Oil on seafloor

On 10 September 2010, Samantha Joye, a professor in the Department of Marine Sciences at the University of Georgia on a research vessel in the Gulf of Mexico announced her team's findings of a substantial layer of oily sediment stretching for dozens of miles in all directions suggesting that a lot of oil did not evaporate or dissipate but may have settled to the seafloor. She describes seeing layers of oily material covering the bottom of the seafloor, in some places more than 2 inches (51 mm) thick on top of normal sediments containing dead shrimp and other organisms. She speculates that the source may be organisms that have broken down the spilled oil and excreted an oily mucus that sinks, taking with it oil droplets that stick to the mucous. "We have to [chemically] fingerprint the oil and link it to the Deepwater Horizon," she says. "But the sheer coverage here is leading us all to come to the conclusion that it has to be sedimented oil from the oil spill, because it's all over the place."[126][127]

By January 2011, USF researchers found layers of oil near the wellhead that were “up to 5 times thicker” than recorded by the team in August 2010. USF's David Hollander remarked, “Oil’s presence on the ocean floor didn’t diminish with time; it grew” and he pointed out, “the layer is distributed very widely,” radiating far from the wellhead.[128]

Independent monitoring

Wildlife and environmental groups accused BP of holding back information about the extent and impact of the growing slick, and urged the White House to order a more direct federal government role in the spill response. In prepared testimony for a congressional committee, National Wildlife Federation President Larry Schweiger said BP had failed to disclose results from its tests of chemical dispersants used on the spill, and that BP had tried to withhold video showing the true magnitude of the leak.[129] On 19 May 2010, BP established a live feed, popularly known as spillcam, of the oil spill after hearings in Congress accused the company of withholding data from the ocean floor and blocking efforts by independent scientists to come up with estimates for the amount of crude flowing into the Gulf each day.[130][131] On 20 May 2010, United States Secretary of the Interior Ken Salazar indicated that the U.S. government would verify how much oil had leaked into the Gulf of Mexico.[132] Environmental Protection Agency Administrator Lisa Jackson and United States Secretary of Homeland Security Janet Napolitano asked for the results of tests looking for traces of oil and dispersant chemicals in the waters of the gulf.[133]

Journalists attempting to document the impact of the oil spill were repeatedly refused access to public areas, and photojournalists were prevented from flying over areas of the gulf to document the scope of the disaster. These accusations were leveled at BP, its contractors, local law enforcement, USCG, and other government officials.[134][135] Scientists also complained about prevention of access to information controlled by BP and government sources.[134] BP stated that its policy was to allow the media and other parties as much access as possible.[134] On 30 June 2010, the Coast Guard put new restrictions in place across the Gulf Coast that prevented vessels from coming within 20 meters (66 ft) "of booming operations, boom, or oil spill response operations".[136] In a press briefing, Coast Guard admiral Thad Allen said the new regulation was related to safety issues.[137] On CNN's 360, host Anderson Cooper rejected the motivation for the restrictions outright.[138] The Civil Air Patrol also monitored the oil spill on behalf of the US Coast Guard. 27 May 2010[139]

The first attempts to stop the flow of oil was the use of remotely operated underwater vehicles to close the blowout preventer valves on the well head; however, all these attempts failed.[81][140] The second technique, placing a 125-tonne (280,000 lb) 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.[141] Attempts to close the well by pumping heavy drilling fluids into the blowout preventer to restrict the flow of oil before sealing it permanently with cement ("top kill") also failed.[142][143]

More successful was positioning a 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.[144] The collected gas was flared and oil stored on the board of drillship Discoverer Enterprise.[145] Before the tube was removed, 924,000 US gallons (22,000 bbl) of oil were collected.[146] By 3 June 2010, BP removed the damaged riser from the top of the blowout preventer and covered the pipe by the cap which connected it to a riser.[147] CEO of BP Tony Hayward stated that as a result of this process the amount captured was "probably the vast majority of the oil."[148] However, the FRTG member Ira Leifer said that more oil was escaping than before the riser was cut and the cap containment system was placed.[149]

On 16 June 2010, a second containment system connected directly to the blowout preventer became operational carrying oil and gas to service vessels where it was immolated in a clean-burning system.[150][150][151]

On 5 July 2010, BP announced that its one-day oil recovery effort accounted for about 25,000 barrels (4,000 m3) of oil, and the flaring off of 57.1 million cubic feet (1.62×106 m3) of natural gas. The total oil collection to date for the spill was estimated at 660,000 barrels (105,000 m3).[152] 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 2010.[100]

On 10 July 2010, the containment cap was removed to replace it with a better-fitting cap consisting of a Flange Transition Spool and a 3 Ram Stack ("Top Hat Number 10").[153][154] On 15 July BP tested the well integrity by shutting off pipes that were funneling some of the oil to ships on the surface, so the full force of the gusher from the wellhead went up into the cap.[155][156] The attempt to cap the wellhead was successful and mud and cement were later pumped in through the top of the well to reduce the pressure inside it, providing a temporary stop to the flow of oil.[13]

Considerations of using explosives

In mid-May, United States Secretary of Energy Steven Chu assembled a team of nuclear physicists, including hydrogen bomb designer Richard Garwin and Sandia National Laboratories director Tom Hunter.[157] On 24 May 2010, BP ruled out conventional explosives, saying that if blasts failed to clog the well, "We would have denied ourselves all other options."[158]

Permanent closure

Transocean's Development Driller III started drilling a first relief well on 2 May 2010. GSF Development Driller II started drilling a second relief on 16 May 2010.[159][160][161][162][163][164] On 3 August 2010, first test oil and then drilling mud was pumped at a slow rate of approximately 2 barrels (320 L) per minute into the well-head. Pumping continued for eight hours, at the end of which time the well was declared to be "in a static condition."[165] On 4 August, BP began pumping cement from the top, sealing that part of the flow channel permanently.[166]

On 3 September 2010, the 300 ton failed blowout preventer was removed from the well and a replacement blowout preventer was placed on the well.[167][168] On 16 September, the relief well reached its destination and pumping of cement to seal the well began.[169] The well was effectively killed on 19 September 2010.[170][170]

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