Deepwater Horizon

2010

Macondo Prospect, the blowout, the largest spill Location: Gulf of Mexico, Mississippi Canyon Block 252 · Coordinates: 28.74°N 88.37°W · Casualties: 11 · Survivors: 115 · Depth: 1,500 m (rig) · 4,000 m (well) · Cause: blowout · fire — Blowout of the Macondo Prospect well on the evening of 20 April 2010 at the BP-operated Deepwater Horizon rig. Gas rose up the drill string and ignited on deck at 21:49. The blowout preventer failed to seal; the rig burned for 36 hours and sank on 22 April. · Fate: sunk · well capped September 2010 · Type: semi-submersible drilling rig · Transocean · Tonnage: 32,588 tons · Crew: 126 · Flag: Marshall Islands · Launched: 2001 Transocean semi-submersible drilling rig, contracted to BP, drilling the Macondo Prospect well 66 kilometres off the Louisiana coast. The well blew out on the evening of 20 April 2010; gas rose up the drill string and ignited on deck at 21:49. The rig burned for 36 hours before sinking. 11 dead. The largest marine oil spill in history poured for 87 days until the well was finally capped: 4.9 million barrels of crude into the Gulf of Mexico. The Vessel Deepwater Horizon was a semi-submersible deepwater drilling rig owned and operated by Transocean Ltd., the world's largest offshore drilling contractor. She was built at Hyundai Heavy Industries in Ulsan, South Korea, delivered in 2001, and operated under a nine-year charter to BP for ultra-deepwater exploratory drilling in the Gulf of Mexico. Her design was a dynamic-positioning, fifth-generation semi-submersible: two parallel pontoons supporting six columns that in turn supported the main deck structure, 121 metres long and 78 metres wide, with a drilling derrick rising 80 metres above the deck. She was one of the most capable drilling rigs in the world. Her operational specifications allowed drilling in water depths of 2,400 metres to a drilled-well depth of 9,100 metres, the outer envelope of ultra-deepwater oil exploration in 2010. She was classed by Det Norske Veritas and flagged under the Marshall Islands, a conventional ownership structure for offshore rigs that placed her nominally outside American regulatory jurisdiction while she operated in the American exclusive economic zone. In February 2010 she was assigned to BP's Macondo Prospect, a 50 per cent BP-owned exploratory lease in Mississippi Canyon Block 252, 66 kilometres off the Louisiana coast. The Macondo well had been drilled from 6 February 2010 and had encountered difficulties throughout: gas kicks, loss of drilling fluid, issues with the blowout preventer, pressure discrepancies that suggested hydrocarbons The Disaster The gas ignited at 21:49:30 on 20 April 2010. The first explosion destroyed the drill floor, the mud-gas separator, and the forward helideck; the second explosion at approximately 21:51 spread the fire through the accommodation block. Eleven crew members, all working in or near the drill floor or mud-processing spaces, died in the first ninety seconds. The surviving 115 crew were evacuated by lifeboat and by rescue vessels over the following two hours; all of them reached the surface ship Damon B. Bankston by early morning on 21 April. The rig burned for 36 hours. The drilling mud and diesel aboard fed a fire that the Louisiana Coast Guard and U.S. Navy firefighting support could not extinguish. She sank at 10:22 on 22 April 2010, coming to rest on the seabed 450 metres northwest of the wellhead, broken into three large sections. The riser pipe connecting her former position to the seafloor bent and separated; the Macondo well began releasing oil and gas to the Gulf of Mexico at a measured rate of 62,000 barrels per day. The well continued to flow for 87 days. Every attempt to close it short of a relief well failed, from the initial "top kill" drilling-mud injection through the "junk shot" polymer attempt. On 15 July 2010 a newly-built capping stack was successfully mated to the wellhead and sealed the flow; the final cement kill of the well from two relief wells was completed on 19 September 2010. Approximately 4.9 million barrels of crude oil had been released into the Gulf