DEEPWATER HORIZON OIL SPILL

Deepwater Horizon oil spill, also called Gulf of Mexico oil spill, largest marine oil spill in history, caused by an April 20, 2010, explosion on the Deepwater Horizon oil rig—located in the Gulf of Mexico, approximately 41 miles (66 km) off the coast of Louisiana—and its subsequent sinking on April 22. About 1,300 miles (2,100 km) of the U.S. Gulf Coast covered in oil. Massive harm done to wildlife in and around the Gulf of Mexico, including the deaths of an estimated 800,000 birds and 65,000 turtles. Release of an estimated 134 million to 206 million gallons of oil into the Gulf of Mexico. As much as 20 percent of the oil spilled may have sunk to the bottom of the ocean, damaging deep-sea ecosystems.


The Deepwater Horizon rig, owned and operated by offshore-oil-drilling company Transocean and leased by oil company BP, was situated in the Macondo oil prospect in the Mississippi Canyon, a valley in the continental shelf. The oil well over which it was positioned was located on the seabed 4,993 feet (1,522 metres) below the surface and extended approximately 18,000 feet (5,486 metres) into the rock. On the night of April 20 a surge of natural gas blasted through a concrete core recently installed by contractor Halliburton in order to seal the well for later use. It later emerged through documents released by Wikileaks that a similar incident had occurred on a BP-owned rig in the Caspian Sea in September 2008. Both cores were likely too weak to withstand the pressure because they were composed of a concrete mixture that used nitrogen gas to accelerate curing.
Once released by the fracture of the core, the natural gas traveled up the Deepwater rig’s riser to the platform, where it ignited, killing 11 workers and injuring 17. The rig capsized and sank on the morning of April 22, rupturing the riser, through which drilling mud had been injected in order to counteract the upward pressure of oil and natural gas. Without any opposing force, oil began to discharge into the gulf. The volume of oil escaping the damaged well—originally estimated by BP to be about 1,000 barrels per day—was thought by U.S. government officials to have peaked at more than 60,000 barrels per day. Although BP attempted to activate the rig’s blowout preventer (BOP), a fail-safe mechanism designed to close the channel through which oil was drawn, the device malfunctioned. Forensic analysis of the BOP completed the following year determined that a set of massive blades known as blind shear rams—designed to slice through the pipe carrying oil—had malfunctioned because the pipe had bent under the pressure of the rising gas and oil. Efforts in May to place a containment dome over the largest leak in the broken riser were thwarted by the buoyant action of gas hydrates—gas molecules in an ice matrix—formed by the reaction of natural gas and cold water. When an attempt to employ a “top kill,” whereby

Payment by oil company BP of $65 billion in compensation to people impacted by the spill.