On April 20, 2010, an explosion and fire occurred on the Deepwater Horizon semi-submersible mobile offshore drilling unit, which was owned and operated by Transocean and drilling for BP in the Macondo Prospect oil field about 40 miles (64 km) southeast off the Louisiana coast. The explosion and subsequent fire resulted in the sinking of the Deepwater Horizon and the deaths of 11 workers; 17 others were injured. The same blowout that caused the explosion also caused an oil well fire and a massive offshore oil spill in the Gulf of Mexico, considered the largest accidental marine oil spill of all time, and the largest environmental disaster in United States history.
Background
Deepwater Horizon
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). Press releases from Transocean state the platform had historically been used for deeper wells, including the deepest underwater gas and oil well. The $560 million platform was built by Hyundai Heavy Industries in South Korea and completed in 2001. It was owned by Transocean, operated under the Marshallese flag of convenience, and was under lease to BP until September 2013. 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. 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. The platform commenced drilling in February 2010 at a water depth of approximately 5,000 feet (1,500 m). At the time of the explosion the rig was drilling an exploratory well. 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. 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.
Transocean safety record
The rig owner, Transocean, had a "strong overall" safety record with no major incidents for 7 years. However, a Wall Street Journal analysis "painted a more equivocal picture" with Transocean rigs being disproportionately responsible for safety related incidents in the Gulf and industry surveys reporting concerns over falling quality and performance. Between 2005 and 2007, Transocean was the owner of 30% of oil rigs active in the Gulf, and 33% of the incidents that triggered a Minerals Management Service (MMS) investigation took place on Transocean rigs. However, in the 3 years from 2008 to February 15, 2010, Transocean was the owner of 42% of rigs active in the Gulf but was responsible for 73% of incidents. Industry surveys saw this as an effect of its November 2007 merger with rival GlobalSantaFe. Transocean was described as having had previous problems with both cement seals (in 2005) and blowout preventers (in 2006), both the suspected cause of the Deepwater Horizon disaster; however, the company stated that cementing was a task completed by third party laborers, and that it had "a strong maintenance program to keep blowout preventers working". 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. 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. 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. [BP spokesperson Toby Odone] wouldn't comment on BP's relationship with Transocean after the Gulf disaster but said BP continues to use Transocean rigs.
Pre-explosion risks and precautions
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". 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. 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. In addition, following a loosening of regulations in 2008, BP was not required to file a detailed blowout plan.
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. 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. 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.
Pre-explosion problems and warnings
The US Coast Guard had issued pollution citations for Deepwater Horizon 18 times between 2000 and 2010 and had investigated 16 fires and other incidents. These incidents were considered typical for a Gulf platform and were not connected to the April 2010 explosion and spill. The Deepwater Horizon had other serious incidents, including one in 2008 in which 77 people were evacuated from the platform when it tilted and began to sink after a section of pipe was incorrectly removed from the platform's ballast system.
The American Bureau of Shipping last inspected the rig's failed blowout preventer in 2005.
Internal BP documents show that BP engineers had concerns as early as 2009 that the metal casing that BP wanted to use might collapse under high pressure. According to a number of rig workers, it was understood that workers could get fired for raising safety concerns that might delay drilling. David Rainey, BP Gulf of Mexico Exploration Manager, was putting his staff and the drilling department under extreme pressure to finish the Macondo well and to move the rig to the next exploration prospect. Rainey was angry that the MC 252 well was over budget and needed to be finished. Gulf of Mexico engineers were not satisfied that they had a proper leak off test and had concerns as to cement integrity. Rainey pressured them to complete the well; no cement bond log was run. The technical staff wanted to re-squeeze the well, but Rainey would not accept this recommendation.
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. The rig's mechanic stated that the well had been experiencing problems for months, and that the drill repeatedly kicked due to resistance from high gas pressure. On March 10, a BP executive emailed the Minerals Management Service about a stuck pipe and well control situation at the drilling site, and stated that BP would have to plugback the well. A confidential survey commissioned by Transocean weeks before the explosion stated that workers were concerned about safety practices and feared reprisals if they reported mistakes or other problems. The survey raised concerns "about poor equipment reliability, which they believed was a result of drilling priorities taking precedence over maintenance." The survey found that "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 blowout preventer was damaged in a previously unreported accident in late March. According to Transocean, workers had been performing standard routines and had no indication of any problems prior to the explosion.
By April 20, the operation was running five weeks late.
An April draft of a BP memo warned that the cementing of the casing was unlikely to be successful. Halliburton has said that it had finished cementing 20 hours before the blowout but had not yet set the final cement plug. A nitrogen-foamed cement was used which is more difficult to handle than standard cement.
Patrick O'Bryan, BP Vice President of drilling, was on the platform two hours prior to the explosion to celebrate seven years without a "lost-time incident" with the rig's crew. 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.
Preliminary findings from BP's internal investigation indicated several serious warning signs in the hours prior to the blowout. Equipment readings indicated gas bubbling into the well, which could signal an impending blowout. The heavy drilling mud in the pipes initially held down the gas. 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.
An article released by The Guardian in 2010, the year of the explosion, reported that the accident could have been avoided had BP implemented better management and communication.
Blowout
The fire aboard the Deepwater Horizon reportedly started at 9:56 p.m. CDT on April 20.
Transocean employees on the vessel stated that the electric lights flickered, followed by two strong vibrations. Jim Ingram stated that "on the second [thud], we knew something was wrong." After the explosion, Adrian Rose stated that abnormal pressure had accumulated inside the marine riser and as it came up it "expanded rapidly and ignited." According to 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. Rose said the event was basically a blowout. Survivors described the incident as a sudden explosion that gave them less than five minutes to escape as the alarm went off.
The explosion was followed by a fire that engulfed the platform. After burning for more than a day, Deepwater Horizon sank on April 22. The Coast Guard stated on April 22 that it received word of the sinking at approximately 10:21 am.
On Sept. 8, BP published a report that suggested that the ignition source was the released gas entering 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.
Casualties and rescue efforts
Survivors
According to officials, 126 people 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.