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) is a massive oil spill in the Gulf of Mexico that is the largest offshore spill in U.S. history and among the largest oil spills in history. The spill stemmed from a sea-floor oil gusher that resulted from the April 20, 2010 Deepwater Horizon drilling rig explosion. The explosion killed 11 platform workers and injured 17 others. On July 15, the leak was largely stopped by capping the gushing oil wellhead. The drilling of relief wells to permanently close the well is ongoing.
The quasi-official Flow Rate Technical Group estimated the oil well was leaking 35,000 to 60,000 barrels (1,500,000 to 2,500,000 US gallons; 5,600 to 9,500 cubic metres) of crude oil per day. This volume is approximately equal to the 1989 Exxon Valdez oil spill every four to seven days. The exact flow rate is uncertain due to the difficulty of installing measurement devices at that depth and is a matter of debate. The resulting oil slick covered at least 2,500 square miles (6,500 km2), fluctuating daily depending on weather conditions. Scientists have also reported immense underwater plumes of dissolved oil not visible at the surface.
The spill continues to cause extensive damage to marine and wildlife habitats as well as the Gulf’s fishing and tourism industries. Crews have been working to protect hundreds of miles of beaches, wetlands and estuaries along the northern Gulf coast, using skimmer ships, floating containment booms, anchored barriers, and sand-filled barricades along shorelines. 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.
Background
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). It was owned by Transocean, operated under the Marshallese flag of convenience, and was under lease to BP from March 2008 to September 2013. 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. 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. 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. BP leased the mineral rights for Macondo at the Minerals Management Service’s lease sale in March 2008.
During March and early April, several platform workers and supervisors expressed concerns with well control. At approximately 9:45 p.m. CDT 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. Most of the workers were evacuated by lifeboats or were airlifted out by helicopter, but eleven workers were never found despite a three-day Coast Guard search operation, and are presumed to have died in the explosion. 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.
On the afternoon of April 22, a large oil slick began to spread at the former rig site. Two remotely operated underwater vehicles (ROVs) unsuccessfully attempted to cap the well. BP announced that it was deploying a ROV to the site to assess whether oil was flowing from the well. On April 23, a ROV reportedly found no oil leaking from the sunken rig and no oil flowing from the well. 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. The following day, April 24, Landry announced that a damaged wellhead was indeed leaking oil into the Gulf and described it as “a very serious spill”. BP has not given a cause for the explosion. According to the US Congressional investigation the rig’s blowout preventer, a fail-safe device fitted at the base of the well, built by Cameron International Corporation, had a hydraulic leak and a failed battery, and therefore failed.
Investigations
On April 22 the United States Coast Guard and the Minerals Management Service launched an investigation of the possible causes of the explosion. On May 11 the Obama administration requested the National Academy of Engineering conduct an independent technical investigation to determine the root causes of the disaster so that corrective steps could be taken to address the mechanical failures underlying the accident. On May 22 President Obama announced that he had issued Executive Order 13543 establishing the bipartisan National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, with former Florida Governor and Senator Bob Graham and former Environmental Protection Agency Administrator William K. Reilly serving as co-chairs. The purpose of the commission is to “consider the root causes of the disaster and offer options on safety and environmental precautions.” On June 1 U.S. Attorney General Eric Holder announced that he has opened an investigation of the oil spill. According to Holder, the Justice Department is interviewing witnesses as part of a criminal and civil investigation. Besides BP, the investigation could apply to other companies involved in the drilling of the damaged well.
The United States House Committee on Energy and Commerce has conducted a number of hearings. On June 17, CEO of BP Tony Hayward testified before the Committee. The heads of Anadarko and Mitsui’s exploration unit will testify before the Committee July 22. On April 30, the Committee asked Halliburton to brief it as well as provide any documents it might have related to its work on the Macondo well. Attention has focused on the cementing procedure and the blowout preventer, which failed to fully engage. A number of significant problems have been identified with the blowout preventer: There was a leak in the hydraulic system that provides power to the shear rams. The underwater control panel had been disconnected from the pipe ram, and instead connected to a test ram. The blowout preventer schematic drawings, provided by Transocean to BP, do not correspond to the structure that is on the ocean bottom. The shear rams are not designed to function on the joints where the drill pipes are screwed together or on tools that are passed through the blowout preventer during well construction. The explosion may have severed the communication line between the rig and the sub-surface blowout preventer control unit such that the blowout preventer would have never received the instruction to engage. Before the backup dead man’s switch could engage, communications, power and hydraulic lines must all be severed, but it is possible hydraulic lines were intact after the explosion. Of the two control pods for the deadman switch, the one that has been inspected so far had a dead battery. Employee Tyrone Benton told the BBC on June 21 that a leak was spotted on a crucial piece of equipment in the oil rig’s blowout preventer weeks before the accident, and that Transocean and BP were emailed about it.
According to the testimony of Doug Brown, the chief mechanic on the Deepwater Horizon, on May 26 at the joint U.S. Coast Guard and Minerals Management Service hearing, a BP representative overruled Transocean employees and insisted on displacing protective drilling mud with seawater just hours before the explosion. One of the BP representatives on the board responsible for making the final decision, Robert Kaluza, refused to testify on the Fifth Amendment grounds that he might incriminate himself; Donald Vidrine, another BP representative, cited medical reasons for his inability to testify, as did James Mansfield, Transocean’s assistant marine engineer on board.
The House Energy and Commerce Committee is investigating the incident. In a statement made in June they 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.
In a June 18 statement, Jim Hackett, the CEO of Anadarko Petroleum Corporation, said research “indicates BP operated unsafely and failed to monitor and react to several critical warning signs during the drilling. … BP’s behavior and actions likely represent gross negligence or willful misconduct.” BP responded by strongly disagreeing with the Anadarko statement and said that, despite being contractually liable for sharing clean-up costs, Anadarko is “refusing to accept responsibility for oil spill removal costs and damages”. BP has sent Anadarko a bill for $272.2 million; Anadarko is “assessing our contractual remedies”.
Other Information
- Location : Gulf of Mexico near Mississippi River Delta
- Date : April 20, 2010 – present
- Cause : Wellhead blowout
- Casualties : 13 dead 11 killed on Deepwater Horizon, 2 additional oil-related deaths, 17 injured
- Operator : Transocean under contract for BP
- Volume : up to 100,000 barrels (4,200,000 US gallons; 16,000 cubic meters) per day; up to four million barrels (170 million gallons) total (as of July 26, 2010) As much as 180m gallons (4.28million barrels)
- Area : 2,500 to 68,000 sq mi (6,500 to 180,000 km2)
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