The gusher, now estimated by the quasi-official Flow Rate Technical Group to be flowing at 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, originates from a deepwater wellhead 5,000 feet (1,500 m) below the ocean surface.The exact spill flow rate is uncertain due to the difficulty of installing measurement devices at that depth and is a matter of ongoing debate.The resulting oil slick covers a surface area of at least 2,500 square miles (6,500 km2), with the exact size and location of the slick fluctuating from day to day depending on weather conditions. Scientists have also reported immense underwater plumes of oil not visible at the surface.
During March and April 2010, 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 up and out of the drill column marine riser, 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 furiously 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".
As of June 25, BP has not given a cause for the explosion.
Short-term efforts:
Oil containment dome under construction in Port Fourchon, Louisiana at Wild Well Control on April 26.BP engineers have attempted a number of techniques to control or stop the oil spill. The first and fastest was to place a 125-tonne (280,000 lb) container dome over the largest of the well leaks and pipe the oil to a storage vessel on the surface. BP deployed the system on May 7–8 but it failed when gas leaking from the pipe combined with cold water to form methane hydrate crystals that blocked up the steel canopy at the top of the dome. The excess buoyancy of the crystals clogged the opening at the top of the dome where the riser was to be connected.
Following the failure, on May 11 a smaller containment dome, dubbed a "top hat", was lowered to the seabed. Like the first containment dome, the dome has been deployed successfully in the past but not at such a depth. The "top hat" dome originally was planned as BP's next attempt to control the spill and there has been no explanation for why BP engineers decided to try the insertion tube first.
On May 14 engineers began the process of positioning a 4-inch (100 mm) wide riser insertion tube tool into the 21-inch (530 mm) wide burst pipe. After three days, BP reported the tube was working. Collection rates varied daily between 1,000 and 5,000 barrels (42,000 and 210,000 US gallons; 160 and 790 cubic metres), the average being 2,000 barrels (84,000 US gallons; 320 cubic metres) a day, as of May 21. The collected gas rate ranged between 4 and 17 million cubic feet per day (110×10^3 and 480×10^3 m3/d). The gas was flared and oil stored on the board of drillship Discoverer Enterprise. 924,000 US gallons (22,000 barrels) of oil was collected before removal of the tube so shutdown efforts could begin.
BP next tried to shut down the well completely using a technique called "top kill". The process involves pumping heavy drilling fluids through two 3-inch (7.6 cm) lines into the blowout preventer that sits on top of the wellhead. This would first restrict the flow of oil from the well, which then could be sealed permanently with cement. The top kill procedure, approved by the Coast Guard on May 25, commenced on May 26 and, according to BP sources, while failure could be evident in minutes or hours it might take "a day or two" before its success could be determined. On May 27 Admiral Thad Allen indicated that engineers had succeeded in stopping the flow of oil and gas into the Gulf of Mexico. He further stated that the well still had low pressure, but cement would be used to cap the well permanently as soon as the pressure hit zero. However, BP officials said it was not possible to tell how far down the well the mud may have reached and declined to speculate on the odds of actually stopping the flow. "We have some indications of partial bridging which is good news. I think it's probably 48 hours before we have a conclusive view." On May 29 BP announced that the attempt to clog the ruptured oil well with "junk" had failed.
The Q4000 and the Discoverer Enterprise during the failed top kill procedureAfter three consecutive failed attempts at the top kill, on May 29 BP moved on to their next contingency option, the Lower Marine Riser Package (LMRP) Cap Containment System. The operational plan first involved cutting and then removing the damaged riser from the top of the failed blowout preventer to leave a cleanly-cut pipe at the top of the BOP's LMRP. The cap is designed to be placed over the pipe and connected to a riser from the Discoverer Enterprise drillship, with the intention of capturing most of the oil and gas flowing from the well. During the cutting of the pipe, the diamond blade saw became stuck and was later freed, but BP had to use shears instead and the cut is "ragged", meaning the cap would be harder to fit. The cap was finally attached on June 3. By June 6, Adm. Thad Allen estimated that the amount of oil captured had increased to 10,000 barrels (420,000 US gallons; 1,600 cubic metres) per day. BP's CEO Tony Hayward stated his opinion that the amount captured was "probably the vast majority of the oil." However, the live stream of the oil escaping from the capped pipe did not appear to be substantially reduced and Ira Leifer, a member of the government team that estimated the flow rate, claimed that the well pipe was clearly gushing more oil than before the cutting of the pipe to put the cap in place.
Only time will tell if the leak can be stopped, but at what cost to the environment.
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