Deepwater Horizon explosion

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This article is about the explosion of the drilling rig Deepwater Horizon. For the subsequent oil spill, see Deepwater Horizon oil spill. For other related articles, see Deepwater Horizon (disambiguation).
Deepwater Horizon explosion
Deepwater Horizon offshore drilling unit on fire 2010.jpg
Anchor handling tugs and platform supply vessels combat the fire on the Deepwater Horizon while the U.S. Coast Guard searches for missing crew.
Time 22:00 UTC-6
Date April 20, 2010 (2010-04-20)
Location Gulf of Mexico, Louisiana, United States 28°44′12.01″N 88°23′13.78″W / 28.7366694°N 88.3871611°W / 28.7366694; -88.3871611Coordinates: 28°44′12.01″N 88°23′13.78″W / 28.7366694°N 88.3871611°W / 28.7366694; -88.3871611[1]
Killed: 11
Injured: 16
Q4000-Discoverer-Enterprise.jpg This article is part of a series about the
Deepwater Horizon oil spill

The Deepwater Horizon drilling rig explosion refers to the April 20, 2010 explosion and subsequent fire on the Deepwater Horizon semi-submersible Mobile Offshore Drilling Unit (MODU), which was owned and operated by Transocean and drilling for BP in the Macondo Prospect oil field about 40 miles (60 km) southeast of the Louisiana coast. The explosion killed 11 workers and injured 16 others. The explosion caused the Deepwater Horizon to burn and sink, resulting in a massive offshore oil spill in the Gulf of Mexico, considered the largest accidental marine oil spill in the world, and the largest environmental disaster in U.S. history.[2][3][4]


Deepwater Horizon[edit]

Main article: Deepwater Horizon
site of the explosion
site of the explosion
DW Horizon
Location of the Deepwater Horizon on April 20, 2010

The "Deepwater Horizon" was a floating semi-submersible drilling unit — a fifth-generation, ultra-deepwater, dynamically positioned, column-stabilized drilling rig owned by Transocean and built in South Korea. The platform was 396 feet (121 m) long and 256 feet (78 m) wide and could operate in waters up to 8,000 feet (2,400 m) deep, to a maximum drill depth of 30,000 feet (9,100 m).[5] Press releases from Transocean state the platform had historically been used for deeper wells, including the deepest underwater gas and oil well in history at 35,055 feet (10,685 m) in 2009.[6] The $560 million platform was built by Hyundai Heavy Industries in South Korea and completed in 2001.[7] It was owned by Transocean, operated under the Marshalese flag of convenience, and was under lease to BP until September 2013.[8] At the time of the explosion, the Deepwater Horizon was on Mississippi Canyon Block 252, referred to as the Macondo Prospect, in the United States sector of the Gulf of Mexico, about 41 miles (66 km) off the Louisiana coast.[9][10][11] In March 2008, the mineral rights to drill for oil on the Macondo Prospect were purchased by BP at the Minerals Management Service's lease sale.[12] The platform commenced drilling in February 2010 at a water depth of approximately 5,000 feet (1,500 m).[13] At the time of the explosion the rig was drilling an exploratory well.[14] The planned well was to be drilled to 18,360 feet (5,600 m) below sea level, and was to be plugged and suspended for subsequent completion as a subsea producer.[13] Production casing was being run and cemented at the time of the accident. Once the cementing was complete, it was due to be tested for integrity and a cement plug set to temporarily abandon the well.[15]

Transocean safety record[edit]

The rig owner, Transocean, had a "strong overall" safety record with no major incidents for 7 years.[16] However an analysts' review "painted a more equivocal picture"[16] with Transocean rigs being disproportionately responsible for safety related incidents in the Gulf[16] and industry surveys reporting concerns over falling quality and performance.[16] In the 3 years 2005 to 2007 Transocean was the owner of 30% of oilrigs active in the Gulf and 33% of incidents that triggered a Minerals Management Service (MMS) investigation were on Transocean rigs, but in the 3 years from 2008 to 15 February 2010 it owned 42% of rigs but was the owner for nearly 3/4 (73%) of incidents.[16] Industry surveys saw this as an effect of its November 2007 merger with rival GlobalSantaFe.[16] Transocean "has had problems" with both cement seals (2005) and blowout preventers (2006), which are the suspected cause of the Deepwater Horizon loss,[16] although Transocean states cementing is a third party task and it has "a strong maintenance program to keep blowout preventers working".[16] According to the Wall Street Journal online:

"In 2008 and 2009, the surveys ranked Transocean last among deep-water drillers for "job quality" and second to last in 'overall satisfaction'. For three years before the merger, Transocean was the leader or near the top in both measures. Transocean ranked first in 2008 and 2009 in a category that gauges its in-house safety and environmental policies"[16]
"There were few indications of any trouble with the Deepwater Horizon before the explosion. The rig won an award from the MMS for its 2008 safety record, and on the day of the disaster, BP and Transocean managers were on board to celebrate seven years without a lost-time accident. Toby Odone, a BP spokesman, said rigs hired by BP have had better safety records than the industry average for six years running, according to MMS statistics that measure the number of citations per inspection. BP has been a finalist for a national safety award from the MMS for the past two years. Mr. Odone wouldn't comment on BP's relationship with Transocean after the Gulf disaster but said BP continues to use Transocean rigs."[16]

Pre-explosion risks and precautions[edit]

Deepwater Horizon drilling rig prior to the incident.

In February 2009, BP filed a 52 page exploration and environmental impact plan for the Macondo well with the Minerals Management Service (MMS), an arm of the United States Department of the Interior that oversees offshore drilling. The plan stated that it was "unlikely that an accidental surface or subsurface oil spill would occur from the proposed activities".[17] In the event an accident did take place the plan stated that due to the well being 48 miles (77 km) from shore and the response capabilities that would be implemented, no significant adverse impacts would be expected.[17] The Department of the Interior exempted BP's Gulf of Mexico drilling operation from a detailed environmental impact study after concluding that a massive oil spill was unlikely.[18][19] In addition, following a loosening of regulations in 2008, BP was not required to file a detailed blowout plan.[20]

The BP wellhead had been fitted with a blowout preventer (BOP), but it was not fitted with remote-control or acoustically activated triggers for use in case of an emergency requiring a platform to be evacuated. It did have a dead man's switch designed to automatically cut the pipe and seal the well if communication from the platform is lost, but it was unknown whether the switch was activated.[21] Documents discussed during congressional hearings June 17, 2010 indicated that Transocean previously made modifications to the BOP for the Macondo site which increased the risk of BOP failure, in spite of warnings from their contractor to that effect. Regulators in both Norway and Brazil generally require acoustically activated triggers on all offshore platforms, but when the Minerals Management Service considered requiring the remote device, a report commissioned by the agency as well as drilling companies questioned its cost and effectiveness.[21] In 2003, the agency determined that the device would not be required because drilling rigs had other back-up systems to cut off a well.[21][22]

Pre-explosion problems and warnings[edit]

There had been previous spills and fires on the Deepwater Horizon; the US Coast Guard had issued pollution citations 18 times between 2000 and 2010, and had investigated 16 fires and other incidents. The previous fires, spills, and incidents were not considered unusual for a Gulf platform and have not been connected to the April, 2010 explosion and spill.[23] The Deepwater Horizon did, however, have other serious incidents, including one in 2008 in which 77 people were evacuated from the platform when it listed and began to sink after a section of pipe was accidentally removed from the platform's ballast system.[24] By April 20, 2010 the Deepwater Horizon well operation was already running five weeks late.[25] Internal BP documents show that BP engineers had concerns as early as 2009 that the metal casing BP wanted to use might collapse under high pressure.[26] In March 2010, the rig experienced problems that included drilling mud falling into the undersea oil formation, sudden gas releases, a pipe falling into the well, and at least three occasions of the blowout preventer leaking fluid.[26] The rig's mechanic stated that the well had problems for months and that the drill repeatedly kicked due to high gas pressure providing resistance.[25] A confidential survey commissioned by Transocean weeks before the explosion states that workers were concerned about safety practices and feared reprisals if they reported mistakes or other problems.[27] On the day the rig exploded, 79 of the 126 people on the rig were Transocean employees.[27]BP Vice President of drilling, Patrick O'Bryan was on the platform two hours prior to the explosion.[28] He had arrived to celebrate seven years without a "lost-time incident" with the rig's crew.[29]

According to a report by 60 Minutes, the blowout preventer was damaged in a previously unreported accident in late March 2010.[30][31] The American Bureau of Shipping last inspected the rig's failed blowout preventer in 2005.[32] According to Transocean, workers had been performing standard routines and had no indication of any problems prior to the explosion.[33] Preliminary findings from BP's internal investigation released by the House Committee on Energy and Commerce on May 25, 2010 indicated several serious warning signs in the hours just prior to the explosion.[34][35] Equipment readings indicated gas bubbling into the well, which could signal an impending blowout.[26] The heavy drilling mud in the pipes initially held down the gas of the leaking well.[36] A BP official on board the rig directed the crew to replace the drilling mud with lighter seawater even though the rig's chief driller protested.[25] According to a number of rig workers, it was understood that workers could get fired for raising safety concerns that might delay drilling.[25]

On March 10, 2010, a BP executive e-mailed the Minerals Management Service that there was a stuck pipe and well control situation at the drilling site, and that BP would have to plugback the well.[37] A draft of a BP memo in April 2010 warned that the cementing of the casing was unlikely to be successful.[26] Halliburton has said that it had finished cementing 20 hours before the fire, but had not yet set the final cement plug.[23][38] A special nitrogen-foamed cement was used which is more difficult to handle than standard cement.[36]

A House Energy and Commerce Committee statement in June 2010 noted that in a number of cases leading up to the explosion, BP appears to have chosen riskier procedures to save time or money, sometimes against the advice of its staff or contractors.[39]

On July 22, Sky News reported that in a survey commissioned by Transocean workers on Deepwater Horizon raised concerns "about poor equipment reliability, which they believed was a result of drilling priorities taking precedence over maintenance."[40] The survey, carried out in March 2010, said "less than half of the workers interviewed said they felt they could report actions leading to a potentially "risky" situation without any fear of reprisal ... many workers entered fake data to try to circumvent the system. As a result, the company's perception of safety on the rig was distorted", the report concluded.[40]

On July 23, 2010 The New York Times reported that crew members had appeared before a federal panel of investigators, saying that power failures, computer crashes and emergency equipment leaks had occurred within a few weeks of the explosion.[41]

Explosion and fire[edit]

Supply boats continued to battle the fire, viewed from a Coast Guard helicopter

The fire aboard the Deepwater Horizon reportedly started at 9:56 p.m. CDT on April 20, 2010.[25] At the time, there were 126 crew on board: seven employees of BP, 79 of Transocean, as well as employees of various other companies involved in the operation of the rig, including Anadarko, Halliburton and M-I Swaco.[42]

Transocean employees on the vessel state that the lights flickered, followed by two strong vibrations. Transocean employee Jim Ingram stated that "on the second [thud], we knew something was wrong."[43] After the explosion, Transocean executive Adrian Rose stated that abnormal pressure had accumulated inside the marine riser and as it came up it "expanded rapidly and ignited."[15] According to interviews with platform workers conducted during BP's internal investigation, a bubble of methane gas escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before exploding.[44] Rose said the event was basically a blowout.[15] Survivors described the incident as a sudden explosion which gave them less than five minutes to escape as the alarm went off.[45]

The explosion was followed by a fire that engulfed the platform. After burning for more than a day, Deepwater Horizon sank on April 22, 2010.[46] The Coast Guard stated to CNN on April 22, 2010 that they received word of the sinking at approximately 10:21 am.[47]

BP subsequently[when?] produced a report that suggests that the ignition source for the explosion and subsequent fire was as a result of the released hydrocarbons being ingested into the air intakes of the diesel generators, and engulfing the deck area where the exhaust outlets for the main generators were emitting hot exhaust gas.[citation needed]

Casualties and rescue efforts[edit]

A helicopter crew medevac survivors from Deepwater Horizon after the explosion.


According to officials, 126 individuals were on board, of whom 79 were Transocean employees, seven were from BP, and 40 were contracted; several of the BP and Transocean executives were on board for a tour of the rig, maintenance planning, annual goals review, a "Drops" safety campaign, and to congratulate the senior staff of the rig for 7 years of operations without a lost time incident.[33][48]

A total of 115 persons were evacuated.[49][50] Although 94 workers were taken by lifeboat to the Tidewater-owned supply boat Damon Bankston, with no major injuries, four were transported to another vessel, and 17 were evacuated by helicopter to trauma centers in Mobile, Alabama and Marrero, Louisiana.[33] Most were soon released.[33][51][52]

The Coast Guard interviewed the uninjured workers on the Damon Bankston for several hours and then transferred them to another rig; the workers arrived in Port Fourchon, Louisiana, more than 24 hours later. The workers were transported to a hotel in Kenner, Louisiana, where they were provided with food, medical attention, and rooms with showers, and asked to fill out incident response forms. An attorney for a worker who brought suit against Transocean claimed that once the workers got to shore, "they were zipped into private buses, there was security there, there was no press, no lawyers allowed, nothing, no family members" and were coerced into signing the forms before being released .[53][54] Transocean responded, in part, as follows:

"Upon arrival at Port Fourchon, crew members were given an opportunity to leave, however, were encouraged to accept transportation to the Crowne Plaza Hotel in Kenner, Louisiana.

Crew members were offered medical care, rooms and opportunity to go home upon arrival at hotel... . Upon arriving at the hotel, crew members were offered the opportunity to meet with qualified medical professionals, to retire to private rooms where they could eat, shower and sleep, or go home. Only then did Transocean and its representatives present crew members with a standard one-page document that asked them to describe where they were at the time of the incident, what they were doing, and to affirm, if true, that they were not a witness and/or that they were not injured. They were free to complete the form at their leisure, or not at all. Some crew members even took the forms home and returned them more than seven days after the incident." [55]


Initial reports indicated that between 12 to 15 workers were missing;[56] reports soon narrowed the number of missing to nine crew members on the platform floor and two engineers.[44] The United States Coast Guard immediately launched a massive rescue operation involving two Coast Guard cutters, four helicopters, and a rescue plane.[57][58] Two of the cutters continued searching through the night. By the morning of April 22, the Coast Guard had surveyed nearly 1,940 square miles (5,000 km2).[49] On April 23, the Coast Guard called off the search for the 11 missing persons, concluding that "reasonable expectations of survival" had passed.[52][59] Officials concluded that the missing workers may have been near the blast and unable to escape the sudden explosion.[60] Jason C. Anderson, 35, Aaron Dale Burkeen, 37, Donald Clark, 49, Stephen Ray Curtis, 39, Roy Wyatt Kemp, 27, Karl D. Kleppinger Jr., 38, Gordon L. Jones, Keith Blair Manuel, 56, Dewey A. Revette, 48, Shane M. Roshto, 22, and Adam Weise, 24, were named as having died.[61]

Discovery of oil spill[edit]

A remotely operated underwater vehicle attempting to turn on the Deepwater Horizon blowout preventer

On the morning of April 22, 2010 (two days after the blowout accident), CNN quoted Coast Guard Petty Officer Ashley Butler as saying that "oil was leaking from the rig at the rate of about 8,000 barrels (340,000 US gallons; 1,300,000 litres) of crude per day."[62] That afternoon, as a large oil slick spread, Coast Guard Senior Chief Petty Officer Michael O'Berry used the same figure. Two remotely operated underwater vehicles (ROVs) were sent down to attempt to cap the well, but had been unsuccessful.[47] Butler warned of a leak of up to 700,000 US gallons (17,000 bbl) of diesel fuel, and BP Vice President David Rainey termed the incident as being a potential "major spill."[47]

On April 22, 2010, BP announced that it was deploying a remotely operated underwater vehicle to the site to assess whether oil was flowing from the well.[63] Other reports indicated that BP was using more than one remotely operated underwater vehicle and that the purpose was to attempt to plug the well pipe.[64] On April 23, 2010, a remotely operated underwater vehicle reportedly found no oil leaking from the sunken rig and no oil flowing from the well.[65] Coast Guard Rear Admiral Mary Landry expressed cautious optimism of zero environmental impact, stating that no oil was emanating from either the wellhead or the broken pipes and that oil spilled from the explosion and sinking was being contained.[66][67][68][69] The following day, April 24, 2010, Landry announced that a damaged wellhead was indeed leaking oil into the Gulf and described it as "a very serious spill".[70]

Investigation into explosion[edit]

In June, the House Committee on Energy and Commerce said BP should have tested cement at the well, which would have cost $128,000 and taken 8–12 hours.

On September 8, 2010, BP released a 193-page report on its web site. The report says BP employees and those of Transocean did not correctly interpret a pressure test, and both companies neglected ominous signs such as a riser pipe losing fluid. It also says that while BP did not listen to recommendations by Halliburton for more centralizers, the lack of centralizers probably did not affect the cement. BP also said the crew should have redirected the flow of flammable gases. The blowout preventer, removed on September 4, had not reached a NASA facility in time for it to be part of the report. Transocean, responding to the report, blamed "BP's fatally flawed well design."[71]

On November 8, 2010, the inquiry by the Oil Spill Commission revealed its findings that BP had not sacrificed safety in attempts to make money, but that some decisions had increased risks on the rig.[72] However, the panel said a day later that there had been "a rush to completion" on the well, criticizing poor management decisions. "There was not a culture of safety on that rig," co-chair Bill Reilly said.[73] One of the decisions met with tough questions was that BP refuted the findings of advanced modelling software that had ascertained over three times as many centralizers were needed on the rig. It also decided not to rerun the software when it stuck with only six centralizers, and ignored or misread warnings from other key tests, the panel revealed.[74]

A slide briefly appeared on the Oil Spill Commission’s website which enumerated eight “risky” and “unnecessary” steps that BP was deemed to have taken. The New York Times newspaper has published a screenshot of the slide here.[75][76]

Review of seven Major Reports on the Causes of the Blowout indicates that six operations, tests, or equipment functions went wrong in the final 32 hours:

1. Small diameter hole obstructed dirt circulation. The 18,300 ft long 400-ton casing string had a 5,800 ft long lower portion with 7-inch diameter. Most of the hole over this portion of casing was 9.875-inch diameter. However, the lowest 180 ft of 7-inch casing with 4 equi-spaced centralisers was squeezed into an 8.5-inch hole with only 56 ft of rathole bottom clearance. Compressed sediment and granular infill in the 0.75-inch wide annulus (Halliburton’s best practices document recommends 1.5 to 2-inch annular gap tolerance) most probably explains the need for much-higher-than-normal pressure of 3142 psi to liquefy it (at the ninth attempt) and allow mud to circulate. The unexpected high pressure and subsequent lower-than-specified mud flow led to problems 2 and 3.

2. Valves to prevent cement backflow did not close. Weatherford’s Auto-Fill float collar, which includes two flapper-type check valves, was installed at Macondo 180 ft above the reamer shoe at casing bottom. The valves are held open by a 2-inch diameter auto-fill tube to allow the casing to automatically fill with mud while it is lowered down the well. BP’s casing installation procedure stated: "slowly increase (mud) pump rates greater than 8 bpm to convert the float equipment (- 500 - 700 psi) per Weatherford recommendation". As the flow rate drag force during circulation and cementing was only around 30% of that required, the auto-fill tube was almost certainly not ejected and the flapper valves never closed. Some evidence suggests that personnel on the Deepwater Horizon mistakenly believed that the high pressure needed to establish mud circulation had converted the float collar.

3. Cementing inadequate. Cementing proceeded a) without flushing the annulus around the shoe track at sufficiently high rate and duration to ensure full circumferential removal of compressed sediment and good distribution of cement, and b) without converting the float collar to activate its two check valves to prevent cement backflow. Cement quality and strength may have been reduced by contamination on its way down the casing, or by mixing with lower density mud in the rathole. There was no cementing evaluation log at Macondo, which may have shown it to be inadequate.

4. Pressure test wrongly interpreted. Drill pipe was run to 8,367 ft ready for mud displacement. During the "negative pressure test", for which there was no detailed procedure, no flow from the kill line was accepted and 1,400 psi on the drill pipe was ignored.

5. Rising oil and gas not monitored. While displacing the mud with seawater, reservoir fluids rising up the casing should have been detected by water inflow and mud outflow monitoring before arrival of hydrocarbons at the rig floor, but no reasonably accurate outflow versus inflow observations were made.

6. Fail-safe on seabed wellhead was unable to close. After uncontrolled arrival of oil and gas at the rig floor, the blind-shear rams in the BOP stack failed to close due to the presence of off-centre drill pipe.


On April 21, 2011, BP filed $40 billion worth of lawsuits against rig owner Transocean, cementer Halliburton and blowout-preventer manufacturer Cameron. The oil firm alleged that failed safety systems and irresponsible behaviour of contractors had led to the explosion, including claims that Halliburton "negligently" failed to use cement-modelling software OptiCem properly to analyze safe well requirements. Part of the modelling concern was about the number of stabilising devices, known as centralisers, the well required: 21 called-for v. 6 used.[77]

In May, 2011, MOEX Offshore, which owned a 10% stake in the well through a subsidiary and which in turn itself was majority-owned by Mitsui & Co., agreed to pay US$1.07 billion to settle BP claims against it over the accident. Some analysts had thought BP would realize a larger settlement from MOEX but there was also relief to have a first step toward resolving the multiple claims. BP’s most recent estimate at the time was that the spill would cost $41.3 billion. Anadarko Petroleum held a 25% stake in the Macondo well and was an immediate focus of attention with MOEX's agreement. Also the Department of Justice was still at the time investigating whether BP was "grossly negligent" in the spill. Such a determination could lead to a "much larger liability under the Clean Water Act,” a financial analyst said. With MOEX agreeing to share in the financial burden—though "the agreement isn’t an admission of liability by either party"—the possibility of such a ruling by the Department of Justice seemed to some to be perhaps lessened.[78]

In June, 2011, supplier Weatherford International settled with BP for $75 million.[79]

In October 2011, Anadarko Petroleum Corporation agreed to pay BP $4 billion and the two companies settled all claims between them.[80] Anadarko yielded its 25% stake in Mississippi Canyon Block 252 (Macondo) to BP in the agreement and BP will indemnify Anadarko for damage claims arising under the U.S. Oil Pollution Act, among other costs.[81]

In December, 2011, Cameron International agreed to pay a $250 million settlement to BP PLC to settle all claims related to the Deepwater Horizon with neither party admitting responsibility. "BP still has not reached a settlement with Transocean ... nor Halliburton.... A trial date over lawsuits related to the accident awaits BP in February (2013)", the update continued.[82]

In September 2014, Halliburton agreed to settle a large percentage of legal claims against it over the Deepwater spill by paying $1.1 billion into a trust by way of three installments over two years.[83]

On 4 September 2014, U.S. District Judge Carl Barbier ruled BP was guilty of gross negligence and willful misconduct under the Clean Water Act (CWA). He described BP's actions as "reckless," while he said Transocean's and Halliburton's actions were "negligent." He apportioned 67% of the blame for the spill to BP, 30% to Transocean, and 3% to Halliburton. Fines would be apportioned commensurate with the degree of negligence of the parties, measured against the number of barrels of oil spilled. Under the Clean Water Act fines can be based on a cost per barrel of up to $4,300, at the discretion of the judge. The number of barrels was in dispute at the conclusion of the trial with BP arguing 2.5 million barrels were spilled over the 87 days the spill lasted, while the court contended 4.2 million barrels were spilled. BP issued a statement strongly disagreeing with the finding, and saying the court's decision would be appealed.[84]

In July of 2015 BP reached an $18.7bn settlement with the US government, the states of Alabama, Florida, Louisiana, Mississippi and Texas, as well as 400 local authorities. To date BP’s cost for the clean-up, environmental and economic damages and penalties has reached $54bn.[85]

See also[edit]


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