February – BP files a 52 page exploration and environmental impact plan for the Macondo well with the MMS. The plan stated that it was "unlikely that an accidental surface or subsurface oil spill would occur from the proposed activities". In the event an accident did take place the plan stated that due to the well being 48 miles (77 km) from shore and the response capabilities that would be implemented, no significant adverse impacts would be expected.
April 6 – The Department of the Interior exempted BP's Gulf of Mexico drilling operation from a detailed environmental impact study after concluding that a massive oil spill was unlikely.
June 22 – Mark E. Hafle, a senior drilling engineer at BP, warns that the metal casing for the blowout preventer might collapse under high pressure.
February 15, 2010 – Deepwater Horizon drilling rig, owned by Transocean, begins drilling on the Macondo Prospect. The planned well was to be drilled to 18,000 feet (5,500 m) below sea level, and was to be plugged and suspended for subsequent completion as a subsea producer.
April 1 – Halliburton employee Marvin Volek warns that BP's use of cement "was against our best practices."
April 6 – MMS issues permit to BP for the well with the notation, "Exercise caution while drilling due to indications of shallow gas and possible water flow."
April 9 – BP drills last section with the wellbore 18,360 feet (5,600 m) below sea level but the last 1,192 feet (363 m) need casing. Halliburton recommends liner/tieback casing that will provide 4 redundant barriers to flow. BP chooses to do a single liner with fewer barriers that is faster to install and cheaper ($7 to $10 million).
April 14 – Brian Morel, a BP drilling engineer, emails a colleague "this has been a nightmare well which has everyone all over the place."
April 15 – Morel informs Halliburton executive Jesse Gagliano that they plan to use 6 centralizers. Gagliano says they should use 21. Morel replies in an email, "it's too late to get any more product on the rig, our only option is to rearrange placement of these centralizers." Gagliano also recommends to circulate the drilling mud from the bottom of the well all the way up to the surface to remove air pockets and debris which can contaminate the cement, saying in an email, "at least circulate one bottoms up on the well before doing a cement job." Despite this recommendation, BP cycles only 261 barrels (41.5 m3) of mud, a fraction of the total mud used in the well.
April 15 – MMS approves amended permit for BP to use a single liner with fewer barriers.
April 16 – Brett Cocales, BP's Operations Drilling Engineer, emails drilling engineer Brian Morel confirming the 6 centralizer approach, saying six should be adequate to obtain a proper cement seal in the well. “Who cares, it’s done, end of story, will probably be fine and we’ll get a good cement job,” he wrote, according to a copy of the e-mail cited in court papers. (Halliburton was the cement provider.)
April 17 – Deepwater Horizon completes its drilling and the well is being prepared to be cemented so that another rig will retrieve the oil. The blowout preventer is tested and found to be "functional." Gagliano now reports that using only 6 centralizers "would likely produce channeling and a failure of the cement job."
April 18 – Gagliano's report says "well is considered to have a severe gas flow problem." Schlumberger flies a crew to conduct a cement bond log to determine whether the cement has bonded to the casing and surrounding formations. It is required in rules.
April 19 – Halliburton completes cementing of the final production casing string.
April 20 –
7 am – BP cancels a recommended cement bond log test. Conducting the test would have taken 9–12 hours and $128,000. By canceling the cement test BP paid only $10,000. Crew leaves on 11:15 am flight. BP officials gather on the platform to celebrate seven years without an injury on the rig. The planned moving of the Deepwater Horizon to another location was 43 days past due and the delay had cost BP $21 million.
9:49 pm (CDT) – Andrea Fleytas had been monitoring the dynamic positioning system on the bridge of the Horizon when she felt a jolt. Before she could make sense of it – a rig shaking shock that came out of nowhere – magenta warnings began flashing on her screen. Magenta meant the most dangerous level of combustible gas intrusion.
9:56 pm CDT – Gas, oil and concrete from the Deepwater Horizon explode up the wellbore onto the deck and then catches fire. The explosion kills 11 platform workers and injured 17 others; another 98 people survive without serious physical injury.
April 21 Coast Guard rear admiral Mary Landry named Federal On Scene Coordinator. Coast Guard log reports “Potential environmental threat is 700,000 gallons of diesel on board the Deepwater Horizon and estimated potential of 8,000 barrels per day of crude oil, if the well were to completely blowout. Most of the current pollution has been mitigated by the fire. There is some surface sheening extending up to 2 miles from the source.” The log also reports that two attempts to shut the BOP using an ROV have failed.
April 23 – Coast Guard rear adm. Mary Landry tells CBS "At this time, there is no crude emanating from that wellhead at the ocean surface, er, at the ocean floor...There is not oil emanating from the riser either."Unified Command begins operating out of the Royal Dutch Shell Training and Conference Center in Robert, Louisiana. Search and rescue suspended at 5 pm. Eleven of the 126 people on the rig have perished. Coast Guard log reports, “BP will establish an ICP at Houma, Louisiana today to monitor the response and prepare for potential release estimated potential of 64,000- 110,000 bbls (2 ,688,000- 4,620,000 gal) per day of crude oil if the well were to completely blowout.”
April 24 – In accordance with the existing in situ burn plans, the OSC determined in situ burning was a viable response method for several reasons. First, weather and sea-state did not allow continuous skimming and alternatives were needed. Second, skimmers and dispersants could not completely remove the oil being released from the well. Finally, the OSC determined in situ burning (ISB) was a safe and effective way to remove large volumes of oil from the ocean surface, based on data for in situ burns from previous spills.
April 25 – Oil sheen seen covering 580 square miles (1,500 km2) and is 70 miles (110 km) south of Mississippi and Alabama coastlines and was 31 miles (50 km) from the ecologically sensitive Chandeleur Islands. BP begins process to establish two relief wells.
April 26 – Oil reported 36 miles (58 km) southeast of Louisiana. Booms set up to keep oil from washing ashore. A huge containment chamber is moved to Superior Energy Services subsidiary Wild Well Control in Port Fourchon, Louisiana. BP closing stock price 57.91 Coast Guard log reports “attempts to actuate the blow preventer (BOP) middle rams and blind shears were ineffective due to a hydraulic leak on the valve. Repairs are being worked overnight. The well head continues to discharge approximately 1,000 barrels/day.
April 27 – Slick grows to 100 miles (160 km) across and 20 miles (32 km) from Louisiana coast.
April 28, the National Oceanic and Atmospheric Administration estimated that the leak was likely 5,000 barrels (210,000 US gallons; 790 cubic metres) a day, five times larger than initially estimated by BP. BP announces controlled test to burn oil off the surface was successful. Oil is 20 miles (32 km) east of the mouth of the Mississippi River. MMS postpones 2010 Offshore Industry Safety Awards scheduled to be May 3.
April 29 – Louisiana Governor Bobby Jindal declares a state of emergency. 100,000 feet (30 km) of containment booms were deployed along the coast. By the next day, this nearly doubled to 180,000 feet (55 km) of deployed booms, with an additional 300,000 feet (91 km) staged or being deployed.Rush Limbaugh noting that explosion occurred the day before Earth Day tells his listeners that it's possible the rig could have been sabotage to encourage favorable votes for the carbon tax bill and cap and trade bills. "What better way to head off more oil drilling, nuclear plants, than by blowing up a rig? I'm just noting the timing here."
April 30 – Oil washes ashore at Venice, Louisiana. President Barack Obama halts new offshore drilling unless safeguards are in place. – Coast Guard issues subpoena to Transocean "to maintain the blowout preventer and to not allow anyone or anything to tamper with it" without the Guard's permission. EPA establishes its website epa.gov/bpspill for its response.Sanford Bernstein estimates capping the leaks and cleaning up the spill may cost $12.5 billion.Innocentive launches a website asking people to submit their solutions to the crisis by June 30. On April 30, the United States House Committee on Energy and Commerce asked Halliburton to brief it as well as provide any documents it might have related to its work on the Macondo well.
May 10 – After failed containment dome BP announces plans to apply five feet in diameter containment vessel nicknamed "top hat". BP announces strategy of trying to push mud and debris down the tube to clog it. The strategy is nicknamed "junk shot."
May 11 – BP, Transocean and Halliburton officials testify before Congress blaming each other for the incident. MMS and Coast Guard Joint Investigation Team chaired by USCG Capt. Hung Nguyen and MMS employee David Dykes begin a Joint Marine Board of Investigation into the accident holding the first hearings at the Crowne Plaza Hotel in Kenner, Louisiana where they interview survivors.
May 12 – BP releases first public video of leak and others say the leak is significantly higher than what BP has been saying. One estimate says it could to be 20,000–100,000 barrels (840,000–4,200,000 US gallons; 3,200–15,900 cubic metres) a day.
Chris Oynes, offshore drilling director for the MMS, announces a hurried retirement.
May 19 – Oil washes ashore on mainland Louisiana.
May 21 – BP begins live underwater video broadcasts of the leak.Flow Rate Technical Group established for "scientifically validated information about the amount of oil flowing from BP s leaking oil well." The average daily oil collection rates is 2,000 barrels (84,000 US gallons; 320,000 litres) a day.
May 23 – BP rebuffs EPA order to change its dispersants. BP says that if oil reaches the shore, it would do more environmental harm than if it were dispersed off the coast. It notes that Corexit is the only product that is available in sufficient quantities to deal with the spill.
May 24 – BP says it currently has no plans to use explosives on the well. It also flatly denies it ever considered using a nuclear bomb on the well as some suggested.
May 26 – BP announces plan to force feed heavy drilling mud in a project called "top kill". Doug Brown, the chief mechanic on the Deepwater Horizon, testifies at the joint U.S. Coast Guard and Minerals Management Service hearing that a BP representative overruled Transocean employees and insisted on displacing protective drilling mud with seawater just hours before the explosion.
May 27 – Obama announces a six-month moratorium on new deepwater oil drilling permits in 500 feet (150 m) of water or more. Based on the oil flow estimates by the Flow Rate Technical Group, the United States government increased its estimate at 12,000 to 19,000 barrels (500,000 to 800,000 US gallons; 1,900,000 to 3,000,000 litres) per day.Elizabeth Birnbaum resigns from MMS.
July 10 – Old cap removed from well at 12:37 pm CDT in preparation for a new cap. Oil is expected to flow unabated into the Gulf for 48 hours.
Three ram capping stack installed on the Deep Water Horizon LMRP at 7 pm CDT (0000 GMT). The stack completes the installation of the new 40-ton containment device sealing cap. Tests begin on testing well integrity.
July 15 – BP test cuts off all oil pouring into the Gulf at 2:25 pm. However Thad Allen cautions that it is likely that containment operations will resume following the test.
July 16 – A Whale will not join the containment process after tests show that its skimming operations were "negligible" in comparison to the much smaller and more nimble skimmers.
July 18 – Allen sends Dudley a letter to provide "written procedure for opening the choke valve as quickly as possible" noting tests have "detected seep a distance from the well and undetermined anomalies at the well."
Kent Wells says BP is considering a "static kill" of the well using heavy mud bumped through the new cap in a process known as bullheading.
Donald Vidrine, who was the ranking BP representative on Deepwater Horizon, citing ill health refuses to testify at Coast Guard hearing into the accident.
NOAA reopens one-third of closed area of Gulf to fishing.
BP says an internal investigation has cleared itself of gross negligence in the spill and will publish the findings in the next month.
Ships return after Bonnie turns out not to have been as strong as anticipated.
Towing vessel Pere Ana C pushing the barge Captain Beauford collides with Louisiana-owned oil and natural gas rig C177 in the northern part of Barataria Bay south of Lafitte, Louisiana. 6,000 feet of boom are placed around rig while it is evaluated.
BP board formally announces that Bob Dudley will replace Tony Hayward as BP CEO effective October 1.
Barack Obama and daughter Sasha swim at Alligator Point in Panama City Beach, Fla., Saturday, Aug. 14, 2010.
Flow Rate Technical Group reports that the well initially was dumping 62,000 barrels of oil per day initially after the spill and that it dwindled to 53,000 barrels when it was capped as the well was depleted. This means that 4.9 million barrels were dropped into the Gulf.
September 19 – BP officially declares oil well completely and permanently sealed.
September 29 – Andy Inglis, who headed deepwater drilling operations in the Gulf of Mexico at the time of the spill, steps down as head of the upstream business.
September 30 – Dudley tells the Houston Chronicle, "We don't believe we have been grossly negligent in anything we've seen in any of the investigations." Dudley also announces BP will create a stronger safety division.
November 28 - Booz Allen Hamilton, Inc. announces the hiring of retired U.S. Coast Guard Admiral Thad Allen as a Senior Vice President of Thought Leadership on Law Enforcement, Homeland Security Strategy.
December 15 – According to a feature Associated Press story on the homepage of Time Magazine, the U.S. federal government is suing BP Exploration and Production, Inc., and eight other corporations, for unlimited liability, in an effort to have them pay for the massive expenses involved in the cleanup and environmental recovery from the spill, including damages to natural resources; it also seeks civil penalties under the Clean Water Act.
December 17 – Unified Area Command releases the report from the Operational Science Advisory Team (OSAT) regarding results of sampling and analyses of thousands of water column and sediment samples from the shoreline through deepwater areas. Reference OSAT report at Restorethegulf.gov