The Daily Drilling Report reveals what may have caused the explosion.
According to BP, “before, during or after the cement job, an undetected influx of hydrocarbons entered the wellbore.” In other words, there was a breach somewhere in well integrity that allowed methane gas and possibly other hydrocarbons to enter the well.
BP: “The 9 7/8” casing was tested; the 9 7/8 “casing hanger packoff was set and tested; and the entire system was tested.” This is called a positive pressure test: fluids were injected in the well to increase pressure and to monitor whether the well would retain its integrity. The well passed this test.
Transocean kept a daily drilling report for Deepwater Horizon ( see TRO-Daily.Drilling.Report.04.20.2010 ) keep a daily drilling report. It is an incomplete log that ends at 3 p.m., seven hours before the explosion.
The daily report confirms that three positive pressure tests were conducted in the morning to early afternoon.
BP: “After 16.5 hours waiting on cement, a test was performed on the wellbore below the Blowout Preventer.”
Halliburton completed cementing the well at 12:35 a.m. on April 20 and after giving the cement time to set, a negative pressure test (the fluid pressure inside the well is reduced and the well is observed to see whether any gas leaks into the well through the cement or casing) was conducted around 5 p.m. The results were “not satisfactory” and “inconclusive.” Significant pressure discrepancies were recorded. As a result, another negative pressure test was conducted.
BP: “During this test (the second negative pressure test), 1,400 psi was observed on the drill pipe while 0 psi was observed on the kill and the choke lines.”
Another unsatisfactory test result.
Congressman Waxman explained that the kill and choke lines run from the drill rig 5,000 feet to the blowout preventer at the sea floor. The drill pipe runs from the drill rig through the blowout preventer deep into the well. In the test, the pressures measured at any point from the drill rig to the blowout preventer should be the same in all three lines. But what the test showed was that pressures in the drill pipe were significantly higher.
James Dupree, the BP Senior Vice President for the Gulf of Mexico explained to the House committee that the results could signal that an influx of gas was causing pressure to mount inside the wellbore.
Mr. Dupree told the Committee staff that he believed the well blew moments after the second pressure test. But lawyers for BP contacted the Committee later and provided a different account.
According to BP’s counsel, further investigation has revealed that additional pressure tests were taken, and at 8:00 p.m., company officials determined that the additional results justified ending the test and proceeding with well operations.
According to Waxman, “what we do know is that shortly before 10:00 p.m. – just two hours after well operations apparently resumed – gas surged from the well up the riser and the rig exploded in a fireball.