Saturday, 26 February 2011

Deepwater Horizon oil spill

Deepwater Horizon oil spill
Deepwater Horizon oil spill - May 24, 2010 - with locator.jpg
The oil slick as seen from space by NASA's Terrasatellite on May 24, 2010.
LocationGulf of Mexico near Mississippi River Delta, United States
Coordinates28.736628°N 88.365997°WCoordinates28.736628°N 88.365997°W
DateSpill date: 20 April – 15 July 2010
Well officially sealed: 19 September 2010
CauseWellhead blowout
Casualties11 dead
OperatorTransocean under contract forBP[1]
Spill characteristics
Volumeup to 4,900,000 barrels(206,000,000 US gallons; 779,000 cubic meters)[2]
Area2,500 to 68,000 sq mi (6,500 to 180,000 km2)[3]
The Deepwater Horizon oil spill (also referred to as the BP oil spill, the Gulf of Mexico oil spill, the BP oil disaster or the Macondo blowout)[4][5][6] is an oil spill in the Gulf of Mexico which flowed for three months in 2010. The impact of the spill continues even after the well was capped. It is the largest accidental marine oil spill in the history of the petroleum industry.[7][8][9] The spill stemmed from a sea-floor oil gusher that resulted from the April 20, 2010 explosion of Deepwater Horizon, which drilled on the BP-operatedMacondo Prospect. The explosion killed 11 men working on the platform and injured 17 others.[10] On July 15, the leak was stopped by capping the gushing wellhead,[11] after it had released about 4.9 million barrels (780×103 m3), or 205.8 million gallons of crude oil.[2] It was estimated that 53,000 barrels per day (8,400 m3/d) were escaping from the well just before it was capped.[9] 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.[9] On September 19, the relief well process was successfully completed and the federal government declared the well "effectively dead".[12]
The spill causes extensive damage to marine and wildlife habitats as well as the Gulf'sfishing and tourism industries.[13][14] In late November 2010, 4,200 square miles (11,000 km2) of the Gulf were re-closed to shrimping after tar balls were found in shrimpers' nets.[15]The total amount of Louisiana shoreline impacted by oil grew from 287 miles (462 km) in July to 320 miles (510 km) in late November 2010.[16] In January 2011, an oil spill commissioner reported that tar balls continue to wash up, oil sheen trails are seen in the wake of fishing boats, wetlands marsh grass remains fouled and dying, and that crude oil lies offshore in deep water and in fine silts and sands onshore.[17] A research team found oil on the bottom of the seafloor in late February 2011 that did not seem to be degrading.[18]
Skimmer ships, floating containment booms, anchored barriers, sand-filled barricades along shorelines, and dispersants were used in an attempt to protect hundreds of miles of beaches, wetlands and estuaries from the spreading oil. Scientists have also reported immense underwater plumes of dissolved oil not visible at the surface[19] as well as an 80-square-mile (210 km2) "kill zone" surrounding the blown well.[20]
The U.S. Government has named BP as the responsible party, and officials have committed to holding the company accountable for all cleanup costs and other damage.[21] After its own internal probe, BP admitted that it made mistakes which led to the Gulf of Mexico oil spill.[22]




[edit]Deepwater Horizon drilling rig

Deepwater Horizon prior to explosion. Parts of the rig providing buoyancy are invisible below the waterline in this picture.
Origin of oil spill
Location of the Deepwater Horizon on April 20, 2010
The Deepwater Horizon was a 9-year-old semi-submersible mobile offshore drilling unit, a massive floating, dynamically positioned drilling rig that could operate in waters up to 8,000 feet (2,400 m) deep and drill down to 30,000 feet (9,100 m).[23] The rig was built by South Korean company Hyundai Heavy Industries.[24] It was owned by Transocean, operated under the Marshallese flag of convenience, and was under lease to BP from March 2008 to September 2013.[25] At the time of the explosion, it was drilling an exploratory well at a water depth of approximately 5,000 feet (1,500 m) in the Macondo Prospect, located in the Mississippi Canyon Block 252 of the Gulf of Mexico in the United States exclusive economic zone about 41 miles (66 km) off the Louisiana coast.[26][27]Production casing was being installed and cemented by Halliburton Energy Services. Once the cementing was complete, the well would have been tested for integrity and a cement plug set, after which no further activities would take place until the well was later activated as a subsea producer.[28][29] At this point, Halliburton modelling systems were used several days running to design the cement slurry mix and ascertain what other supports were needed in the well bore.[30] BP is the operator and principal developer of the Macondo Prospect with a 65% share, while 25% is owned by Anadarko Petroleum Corporation, and 10% by MOEX Offshore 2007, a unit of Mitsui.[31] BP leased the mineral rights for Macondo at the Minerals Management Service's lease sale in March 2008.[32]


Vessels combat the fire on theDeepwater Horizon while the United States Coast Guard searches for missing crew
At approximately 9:45 p.mCDT on April 20, 2010, methane gas from the well, under high pressure, shot all the way up and out of the drill column, expanded onto the platform, and then ignited and exploded. Fire then engulfed the platform.[29][33] Most of the workers escaped the rig by lifeboat and were subsequently evacuated by boat or airlifted by helicopter for medical treatment;[34] however, eleven workers were never found despite a three-day Coast Guard search operation,[35] and are presumed to have died in the explosion.[36] Efforts by multiple ships to douse the flames were unsuccessful. After burning for approximately 36 hours, the Deepwater Horizon sank on the morning of April 22, 2010.[37]

[edit]Volume and extent of oil spill

An oil leak was discovered on the afternoon of April 22 when a large oil slick began to spread at the former rig site.[38] According to the Flow Rate Technical Group the leak amounted to about 4.9 million barrels (205.8 million gallons) 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.[2][9]

[edit]Spill flow rate

In their permit to drill the well, BP estimated the worst case flow at 162,000 barrels per day (25,800 m3/d).[39] 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.[40] On April 24, Coast GuardRear Admiral Mary Landry announced that a damaged wellhead was indeed leaking.[41][42] She stated that "the leak was a new discovery but could have begun when the offshore platform sank ... two days after the initial explosion."[41] 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).[41] Outside scientists quickly produced higher estimates, which presaged later increases in official numbers.[43][44][45] Official estimates increased from 1,000 to 5,000 barrels per day (160 to 790 m3/d) on April 29,[46][47] to 12,000 to 19,000 barrels per day (1,900 to 3,000 m3/d) on May 27,[48][49][50][51] to 25,000 to 30,000 barrels per day (4,000 to 4,800 m3/d) on June 10,[52][53][54] and to between 35,000 and 60,000 barrels per day (5,600 and 9,500 m3/d), on June 15.[55][56] 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.[57][58]
Progression of oil spill flow rate estimates
SourceDateBarrels per dayGallons per dayCubic metres per day
BP estimate of hypothetical worst case scenario (assumes no blowout preventer)Permit162,0006,800,00025,800
United States Coast GuardApril 23 (after sinking)000
BP and United States Coast GuardApril 241,00042,000160
Official estimatesApril 291,000 to 5,00042,000 to 210,000790
Official estimatesMay 2712,000 to 19,000500,000 to 800,0001,900 to 3,000
Official estimatesJune 1025,000 to 30,0001,100,000 to 1,300,0004,000 to 4,800
Flow Rate Technical GroupJune 1935,000 to 60,0001,500,000 to 2,500,0005,600 to 9,500
Internal BP documents hypothetical worst case (assumes no blowout preventer)June 20up to 150,000up to 4,200,000up to 16,000
Official estimates[59]August 262,0002,604,0009,857
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 EnforcementU.S. Department of Energy (DOE), and outside academics, led by United States Geological Survey (USGS) director Marcia McNutt.[60][61][62] 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.[63] 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.[46] 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.[19] 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.[64]
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 July 15. 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.[9]

[edit]Spill area and thickness

Oil slicks surround the Chandeleur Islands, Louisiana, in this aerial photo.
The oil's spread was initially increased by strong southerly winds caused by an impending cold front. By April 25, the oil spill covered 580 square miles (1,500 km2) and was only 31 miles (50 km) from the ecologically sensitive Chandeleur Islands.[65] An April 30 estimate placed the total spread of the oil at 3,850 square miles (10,000 km2).[66] The spill quickly approached the Delta National Wildlife Refuge and Breton National Wildlife Refuge.[67] On May 19 both the National Oceanic and Atmospheric Administration and other scientists monitoring the spill with theEuropean 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 Streamalong the U.S. east coast.[68] On June 29, 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.[68][69]
On May 14, 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 says he thinks most of the oil is floating within 1 foot (30 cm) of the surface.[70] The New York Times is tracking the size of the spill over time using data from National Oceanic and Atmospheric Administration, the US Coast Guard and Skytruth.[71]
The wellhead was capped on July 15 and by July 30 the oil appeared to have dissipated more rapidly than expected. Some scientists believe 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 are able to consume it.); winds from storms appeared to have aided in rapidly dispersing the oil, and the clean-up 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, and an unknown amount remains below the surface.[72]
However, many scientists dispute the report's methodology and figures.[73] Scientists said a lot of oil was still underwater and could not be detected.[74] According to the NOAA report released on August 4, about half of the oil leaked into the Gulf remains on or below the Gulf's surface.[75] 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.[76] The federal calculations are based on direct measurements for only 430,000 barrels (18,000,000 US gal) of the oil spilled — the stuff 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.[77] 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".[78] On August 16, University of Georgia scientists said their analysis of federal estimates shows that 80% of that BP 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'.[79]
In a December 3 statement, BP claimed the government overestimated the size of the spill. On the same day, presidential commission staff said that BP lawyers claim the size is overstated by between 20 and 50 percent. A document obtained by The Associated Press, submitted by BP to the commission, NOAA and The Justice Department, says, "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. BP fully intends to present its own estimate as soon as the information is available to get the science right."[80]

[edit]Oil sightings

Oil began washing up on the beaches of Gulf Islands National Seashore on June 1.[81] By June 4, 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.[82] On June 9, oil sludge began entering the Intracoastal Waterway through Perdido Pass after floating booms across the opening of the pass failed to stop the oil.[83] On June 23, 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.[84][85] On June 27, tar balls and small areas of oil reached Gulf Park Estates, the first appearance of oil in Mississippi.[86] Early in July, tar balls reached Grand Isle but 800 volunteers were cleaning them up.[87] On July 3 and July 4, 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 July 5.[88] On July 5, strings of oil were found in theRigolets in Louisiana, and the next day tar balls reached the shore of Lake Pontchartrain.[88][89]
On September 10, 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.[90]
On October 23, it was reported that miles-long stretches of weathered oil had been sighted in West BayTexas 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.[91]
At the end of October, Scientists who were aboard two research vessels studying the spill's impact on sea life announced they had found substantial amounts of oil on the seafloor, contradicting statements by federal officials that the oil had largely disappeared. Kevin Yeager, aUniversity 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, Yeager said. Yeager's team still needs to "fingerprint" the samples in labs to determine definitively that the oil came from BP's well. 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, he said. A second research team also 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.[92]
In late November, Plaquemine Parish, Louisiana coastal zone director P.J. Hahn reported that more than 32,000 US gallons (760 bbl) of oil had been sucked out of nearby marshes in the previous 10 day period. In Barataria Bay, Louisiana, photos and first-hand 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. "In some ways it's worse today," Hahn said, "because the world mistakenly thinks all the oil has somehow miraculously disappeared".[16]

[edit]Underwater oil plumes

On May 15, researchers from the National Institute for Undersea Science and Technology,[93] aboard the research vessel RV Pelican, identified oil plumes in the deep waters of the Gulf of Mexico,[94] 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).[95] Other researchers from the University of Georgia found that the oil may have occupied multiple layers.[96] By May 27, 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.[97] The National Oceanic and Atmospheric Administration (NOAA) conducted an independent analysis of the water samples provided from the 22–28 May 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.[98] Reporting on a study that ended on June 28, 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 very fast and that it may pose a long-lasting threat for marine life deep in the ocean.[99] On July 23, University of South Florida researchers and NOAA released two separate studies confirming subsea plumes of oil resulting from the Deepwater Horizon well.[100] 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).[101][102]
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.[103] He did not challenge the finding 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."[104] Researchers from the Universities of South Florida and Southern Mississippi claim the government tried to squelch their findings. "We expected that NOAA would be pleased because we found something very, very interesting," said Vernon Asper, an oceanographer at the USM. "NOAA instead responded by trying to discredit us. It was just a shock to us."[105] Lubchenco rejected Asper's characterization, saying "What we asked for, was for people to stop speculating before they had a chance to analyze what they were finding."[106] She argued for the necessity of chemically fingerprinting the plumes in order to distinguish them from oil seeps that occur naturally in the Gulf.[107] In a report released on June 8, 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 for certain.[98]
On June 23, NOAA released a report which confirmed the existence of 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:[108] "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".[109]
In October 2010, scientists reported the presence of a continuous plume of over 35 kilometers in length at a depth of about 1100 meters. That plume persisted for several months without substantial degradation.[110]

[edit]Oil on seafloor

On September 10, 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 thick atop 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."[111][112]
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.[113]

[edit]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.[114] On May 19, 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.[115][116] On May 20 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.[117] 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.[118]
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.[119][120] Scientists also complained about prevention of access to information controlled by BP and government sources.[119] BP stated that its policy was to allow the media and other parties as much access as possible.[119] On June 30, 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".[121] In a press briefing, Coast Guard admiral Thad Allen said the new regulation was related to safety issues.[122] On CNN's 360, host Anderson Cooper rejected the motivation for the restrictions outright.[123]
In late June, reacting to the discovery of submerged oil plumes by the Universities of Alabama, and South Florida, BP's High Interest Technology Test (HITT) Team contracted with several independent researchers for the development of new technologies to detect, and map sub-sea dissolved oil plumes. By October, HITT team leader, Ken Lukins, was supervising tests of a variety of sensors off Mobile, Alabama's Dauphin Island. Systems included the CODA-Octopus Acoustic Sensor Array and a helicopter deployed submerged mass spectrometer/fluorescence hydrodynamic dart system created by engineer-pilot, Robert Tur. Both systems were successful, with the helicopter based testing capable of scanning, and 3D real-time mapping of up to 1,400 sq. miles, daily, while the ship-based CODA-Octopus Array was capable of high-resolution 3D scans, up to 120 feet, every 20 minutes. To date, despite both system's ability to prevent commercial fishermen from casting their nets in hydrocarbon plumes, neither system has been green lit by BP's Gulf Coast Restoration Organization (GCRO).