What happened?
On April 20, 2010, the Macondo well in the Gulf of Mexico blew out while being drilled from the Deepwater Horizon. The resulting explosions and fire killed 11 people. The rig later sank, and oil flowed from the subsea well into the Gulf.
President Barack Obama appointed the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling to investigate the disaster, its causes and the regulatory and corporate systems surrounding it. This article uses only the Commission Chief Counsel’s February 17, 2011 report, Macondo: The Gulf Oil Disaster, as its primary source.
The report follows not only cementing, pressure testing and well-control mechanics, but also the emails, last-minute procedures, contractor relationships, calls that were or were not made, and what people were doing while abnormal readings appeared.
12 passages that stood out
The selections emphasize specific exchanges and operating details that are easy to miss in broad accounts of the disaster: “flying by the seat of our pants,” “we are in the dark,” an unused cement-evaluation crew, a crowded drill shack, a ten-minute break, and conversations after a major pressure anomaly.
The report is an original English-language source. Page references below use its printed page numbers. Evaluative conclusions are attributed to the Chief Counsel’s team rather than presented as independent findings by From Reports.
The crew raised pressure nine times to establish mud circulation. At 3,142 psi, a BP engineer emailed that he was still not sure what they had “blown”
At Macondo, the crew needed to circulate drilling mud through the production casing and convert the float equipment into its intended operating state. At first, however, they could not establish circulation.
The crew repeatedly raised pump pressure. On the ninth attempt, pressure reached 3,142 psi, then suddenly dropped and mud began circulating. Rig personnel treated the drop as evidence that the float equipment had converted, although the report notes that the crew never subsequently sustained the flow rate called for by the relevant Weatherford calculations.
BP drilling engineer Brian Morel emailed a Weatherford representative: “Yah we blew it at 3140, still not sure what we blew yet.”
The Chief Counsel’s team later considered multiple possible explanations for the pressure drop, including a clog that cleared or a failure within the float-collar system.
A cement-evaluation team waited on the rig for more than a day, then left on the 11:15 a.m. helicopter without running the log
BP had ordered cement-evaluation services from Schlumberger so a team would be available if the cement job did not go as planned. Technicians arrived over April 18 and 19 and waited on the rig for more than a day.
On the morning of April 20, the Macondo team concluded that the cement job had gone well enough that the evaluation log was unnecessary.
At about 11:15 a.m., the Schlumberger team left the rig on a regularly scheduled BP helicopter without running the cement-evaluation log.
The report says not running the log probably saved about eight hours of rig time.
There had been a special boat or helicopter run every day. A BP email said the well site leaders were “flying by the seat of our pants”
As BP dealt with last-minute decisions over additional centralizers, wells team leader John Guide emailed his supervisor about the pace and manner of operational changes.
He wrote that there had been so many last-minute changes over the previous four days that the well site leaders had “finally come to their wits end.”
Guide said the phrase being used was “flying by the seat of our pants,” and added that a special boat or helicopter run had been made every day.
The same email said that engineering leadership was “driving chaos” and that the operation would not succeed if it continued in the same manner.
A Weatherford technician called his supervisor after learning the added centralizers would not be used. The answer: “Third party, we do what the company man requests”
BP had flown 15 additional centralizers and a Weatherford service technician to the Deepwater Horizon, then ultimately decided not to install the extra centralizers.
According to the report, the Weatherford technician learned of the cancellation only after asking about the work after the expected installation time had passed. He was concerned enough to call his supervisor because he had never been on an installation job that was canceled.
His supervisor told him to defer: “Third party, we do what the company man requests.”
The Chief Counsel’s team says neither the technician nor anyone else at Weatherford pressed the concern with BP.
Eight days before the blowout, a well site leader emailed: “we need procedures” and “we are in the dark”
BP had planned since January 2010 to use the Deepwater Horizon to install a lockdown sleeve and temporarily abandon the Macondo well, but its January drilling program still did not contain the temporary-abandonment procedure.
By April 9, the team knew the final depth of the well and had the information needed to tailor such a procedure to Macondo. Three days later, a well site leader asked the shoreside team for procedures.
On April 12, Murry Sepulvado wrote: “Brian we need procedures for running casing, cementing and T&A work, we are in the dark and nearing the end of logging operations.”
The report says the team then changed the temporary-abandonment procedure at least four times during the nine days before the blowout.
During the troubled negative-pressure test, shift change and a VIP tour made the drill shack “standing room only”
During the negative-pressure test, the crew was already dealing with readings that did not behave as a successful test should.
At about 5:26 p.m., shift relief took place. At roughly the same time, a group of visiting BP and Transocean executives entered the drill shack on a tour.
With both the shift-relief personnel and the tour group present, the drill shack was described as “standing room only.”
One visiting executive recognized that the drilling team appeared confused about something and asked two senior Transocean personnel to remain behind after the tour group left.
A 1,400 psi drill-pipe reading was explained as a “bladder effect.” The Chief Counsel's experts did not support that explanation
In the negative-pressure test, the kill line showed zero pressure and no flow while the drill pipe still held about 1,400 psi. The two readings pointed in different directions.
Personnel on the rig discussed an explanation described as a “bladder effect.” The report says experienced Transocean personnel advocated that view, and the BP well site leaders eventually accepted the test as successful.
The Chief Counsel’s team found no expert it interviewed who supported a “bladder effect” that could explain the pressure readings seen in this test.
The crew then moved on with the temporary-abandonment operation.
The mudlogger stepped away for about ten minutes. At nearly the same time, emptying trip tanks made the flow-out reading rise instead of fall
Just before 9 p.m., mudlogger Joseph Keith told the drill crew he was taking a short break. He went downstairs, used the restroom, got coffee and smoked half a cigarette. The report says he was away for about ten minutes.
At 8:59 p.m., the crew reduced pump rates while also beginning to empty the trip tanks.
Lower pump rates should have reduced the flow-out reading, but fluid from the trip tanks passed the flow-out meter and caused the displayed flow to increase instead. The report says this could have masked a kick indication.
At 9:01 p.m., drill-pipe pressure reversed direction and began to rise. After returning, Keith reviewed the period he had missed but said he did not see anything wrong.
Drill-pipe pressure jumped by about 600 psi. The report saw “no hint of alarm,” and personnel continued talking and joking
At 9:38 p.m., drill-pipe pressure rose by roughly 600 psi. The Chief Counsel’s team describes this as another serious anomaly.
By that point, the crew had already seen several indications that fluids were moving in the well. The report says the signs should have caused alarm.
Instead, the report says there appeared to be “no hint of alarm.” Personnel spoke for several minutes, and one pair joked; witnesses described no sign of concern or hurry.
During this period, the drill crew did not communicate the anomaly to the mudlogger or contact the senior toolpusher, offshore installation manager or well site leader. Within minutes, mud overflowed onto the rig floor and shot toward the top of the derrick.
Multiple combustible-gas alarms sounded, but the general alarm was not triggered immediately. The operator said: “There was a lot going on”
Immediately before the explosions, multiple combustible-gas alarms were sounding on the bridge. Dynamic positioning officer Andrea Fleytas felt the first jolt and saw the alarms but did not immediately activate the rig’s general alarm.
She also received a call from the engine control room asking what was happening and did not instruct the room to shut down the engines at that point.
Asked why she hesitated, Fleytas said: “It was a lot to take in. There was a lot going on.”
She also testified that Transocean had provided no formal training or simulations for responding to combustible-gas alarms.
The anomalous negative-pressure test was not taken to the shoreside engineering team for a second opinion while it was being interpreted
The Chief Counsel’s team found no indication that BP’s well site leaders or the Transocean drilling crew sought outside guidance while deciding whether the anomalous negative-pressure test had passed.
BP had a shoreside engineering team that regularly answered technical questions from the rig. Houston-based wells team leader John Guide later said the pressure readings were the sort of situation in which he would have expected a call.
The report says the well site leaders did not contact BP’s onshore engineers for a second opinion while they were unable to bleed drill-pipe pressure to zero and were interpreting the test.
A communications plan existed, but the report says it did not address the negative-pressure test specifically. One BP employee later mocked the plan’s “weird drawings with boxes & arrows.”
Macondo's risk register did not include safety as an element; it focused on how risks affected time and cost
The Chief Counsel’s team says the Macondo team often made individual decisions that were consistent with efficiency without stepping back to consider the combined safety implications.
It points to the well’s risk register as one example. The register was intended to identify potential problems and the consequences of those hazards.
But the Macondo risk register did not include safety as an element and focused exclusively, according to the report, on the effects risks could have on time and cost.
The report also says there is no indication that the Macondo team used the register once the well entered the Execute stage.
What the report says about the background
The Chief Counsel’s Report does not reduce the disaster to one failed component or one person’s judgment. It examines multiple technical failures — including cement isolation, the negative-pressure test, kick detection and emergency response — alongside failures in communication, risk assessment and the way expertise was divided among BP, Transocean, Halliburton and other contractors.
It also argues that individual decisions could look reasonable in isolation while collectively shifting operations toward time, cost and efficiency without a sufficiently strong process-safety review of their combined effects.