Deepwater Horizon Oil Spill (2010): Blowout in the Gulf of Mexico

The Deepwater Horizon oil spill began on 20 April 2010, when a blowout at BP’s Macondo well in the Gulf of Mexico caused an explosion and fire on the Deepwater Horizon drilling rig, killing 11 workers. For 87 days oil gushed from the broken well 1,500 metres below the surface, before it was capped on 15 July. With an estimated 3 to 4 million barrels released into the sea, it was the largest marine oil spill in United States history, causing severe damage to wildlife, fisheries and coastal communities and leading to record fines.

Background: drilling in deep water

By the 2000s, oil companies were drilling ever further offshore in the Gulf of Mexico, in water more than 1,000 metres deep. Deep-water wells could reach large reservoirs but were technically demanding, with very high pressures and temperatures and equipment that could be reached only by remotely operated submarines.

The Deepwater Horizon was a semi-submersible drilling rig, built in 2001 and owned by Transocean, the world’s largest offshore drilling contractor. BP leased it to drill an exploratory well at the Macondo prospect in Mississippi Canyon Block 252, about 66 kilometres (41 miles) off the Louisiana coast, in roughly 1,500 metres (5,000 feet) of water. The oil-services company Halliburton was responsible for cementing the well.

The Macondo well was behind schedule and over budget. By April 2010 it had reached oil and gas at about 5,600 metres below sea level, and the crew was preparing to seal it temporarily so that a production platform could return later.

The blowout of 20 April 2010

The final steps went wrong. Cement pumped to seal the bottom of the well failed to hold back the oil and gas, a flaw that later investigations linked to the cement mixture and to decisions about how the well was built. On the evening of 20 April, the crew carried out a “negative pressure test” to check the seal. The results showed signs of a problem, but they were misinterpreted and the test was judged a success.

As the crew replaced heavy drilling mud with lighter seawater, oil and gas began to flow into the well. Warning signs were missed for around 40 minutes. At about 9:45 p.m. local time, mud and gas erupted onto the rig floor. The gas reached engines and other sources of ignition and exploded, setting the rig ablaze.

The blowout preventer, a stack of valves on the seabed designed to seal the well in an emergency, failed. Its blind shear ram, meant to cut through the drill pipe and close the well, did not seal it, partly because the pipe had buckled. Eleven men working on or near the drill floor were killed. The other 115 people on board escaped, many by jumping into the sea, and were picked up by the supply vessel Damon B. Bankston. Seventeen were injured.

The fire burned for some 36 hours. On 22 April 2010, the Deepwater Horizon sank, leaving the broken riser pipe on the seabed leaking oil.

Eighty-seven days of oil

At first BP and the US government estimated the leak at about 1,000 barrels a day, then 5,000. Independent scientists studying underwater video argued that the flow was far larger, and a government-appointed Flow Rate Technical Group eventually concluded that it had been around 50,000 to 60,000 barrels a day.

Efforts to stop the leak repeatedly failed. A large containment dome lowered over a leak in early May became clogged with icy gas hydrates. A “top kill”, which pumped heavy mud into the well in late May, could not overcome the pressure. From June a cap and pipes collected part of the oil on ships at the surface. On 15 July a new tightly fitting capping stack finally stopped the flow, 87 days after the blowout.

Two relief wells were drilled to intercept the Macondo well deep below the seabed. Through one of them, engineers pumped in cement, and on 19 September 2010 the federal government declared the well permanently sealed.

Damage to the Gulf

The government estimated the total flow at about 4.9 million barrels, of which roughly 800,000 barrels were captured. In 2015 a federal court ruled that 3.19 million barrels had entered the sea, the figure used to set fines. Much of the oil formed slicks at the surface, while large plumes stayed suspended in deep water.

BP and the authorities used about 1.8 million gallons (about 7 million litres) of chemical dispersants, some of it injected directly at the wellhead for the first time, to break the oil into small droplets. Critics questioned the long-term effects of the dispersants themselves. Surface oil was also burned off and skimmed, and thousands of kilometres of floating boom were laid along coasts.

Oil reached the shores of Louisiana, Mississippi, Alabama and Florida, and some 2,100 kilometres (1,300 miles) of coastline were oiled to some degree, with Louisiana’s marshes hit hardest. At the peak, the federal government closed about 37 percent of US waters in the Gulf of Mexico to fishing. Thousands of oiled birds, sea turtles and marine mammals were recovered, and later studies linked the spill to deaths of dolphins, deep-sea coral damage and harm to fish populations. The full long-term ecological effects are still being studied.

Coastal economies suffered heavily. Fishermen lost their seasons, tourism collapsed along parts of the coast, and a six-month moratorium on deep-water drilling imposed by President Barack Obama’s administration in May 2010 hit oil-industry jobs. Many clean-up workers reported health problems.

Investigations and blame

The National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, appointed by President Obama and co-chaired by former senator Bob Graham and former Environmental Protection Agency head William Reilly, reported in January 2011. It concluded that the blowout was preventable and resulted from a series of identifiable mistakes by BP, Halliburton and Transocean that reflected systemic failures of risk management. It also found that federal regulation had been weak.

The regulator, the Minerals Management Service, was criticised for close ties to the industry and was broken up into separate agencies for leasing, safety enforcement and revenue collection. New rules on well design, blowout preventers and emergency response followed.

BP’s chief executive, Tony Hayward, became a focus of public anger in the United States after a series of poorly received remarks, and he stepped down in October 2010. In June 2010, after meeting President Obama, BP agreed to set up a 20 billion dollar fund to compensate victims.

Penalties and settlements

In November 2012 BP pleaded guilty to 14 criminal counts, including 11 counts of manslaughter related to the deaths of the workers, and agreed to pay 4 billion dollars in criminal penalties. Transocean agreed to pay 1.4 billion dollars in civil and criminal penalties in 2013, and Halliburton pleaded guilty to destroying evidence. Criminal charges against individual employees mostly ended in acquittals or dropped charges.

In September 2014, Judge Carl Barbier of the federal court in New Orleans ruled that BP had been grossly negligent. In 2015 BP agreed a settlement with the US government and five Gulf states worth about 20.8 billion dollars, finalised in 2016 and described by the Justice Department as the largest environmental settlement in US history. BP’s own estimate of its total costs, including clean-up, compensation and penalties, exceeded 60 billion dollars.

Timeline

• 2010, 20 April: Blowout and explosion on the Deepwater Horizon at about 9:45 p.m.; 11 workers are killed.
• 2010, 22 April: The burning rig sinks; oil begins leaking from the riser on the seabed.
• 2010, 27 May: A six-month moratorium on new deep-water drilling is announced.
• 2010, 29 May: BP announces that the “top kill” attempt has failed.
• 2010, 16 June: BP agrees to create a 20 billion dollar compensation fund.
• 2010, 15 July: A capping stack stops the flow of oil after 87 days.
• 2010, 19 September: The well is declared permanently sealed after cementing through a relief well.
• 2012, 15 November: BP pleads guilty to criminal charges and agrees to pay 4 billion dollars.
• 2015, 2 July: BP announces a civil settlement of about 18.7 billion dollars, later finalised at about 20.8 billion.

By the numbers

Legacy

Deepwater Horizon far exceeded the Exxon Valdez oil spill of 1989 in volume, and it was compared with the Santa Barbara oil spill of 1969, which had helped launch the American environmental movement. It showed that the technology for drilling in deep water had outpaced the ability to stop a deep-water blowout, and the industry later developed rapid-response capping systems that could be flown to a damaged well.

The disaster also became part of popular culture, notably through the 2016 film Deepwater Horizon. Scientists used the spill to study how oil behaves in the deep ocean, while the settlement money funded major restoration projects along the Gulf Coast, including rebuilding Louisiana’s eroding wetlands.

Why it matters

The Deepwater Horizon disaster killed 11 workers and caused the worst marine oil spill in US history. It exposed failures by companies and regulators alike, led to the largest environmental penalties ever imposed in the United States, and remains a central example of the risks of offshore oil drilling.