OGJ Washington Editor
WASHINGTON, DC, May 26 -- Information received by the US House Energy and Commerce Committee from BP PLC concerning the Apr. 20 rig accident and oil spill in the Gulf of Mexico confirms many issues raised at the committee’s May 12 hearing, two of its majority leaders said. The interim report also raises significant new questions, they added in a May 25 memorandum to committee members.
The information supplied by BP in a briefing of the committee’s staff identified several new warning signs of problems before the Transocean Ltd.’s Deepwater Horizon semisubmersible rig exploded and sunk into the gulf, killing 11 crew members, committee chairman Henry A. Waxman (D-Calif.) and Oversight and Investigations Subcommittee Chairman Bart Stupak (D-Mich.) said in their memo.
According to BP, they continued, there were three flow indicators from the company’s well before the explosion: One was 51 min before the blast, when more fluid began flow from the well than was being pumped in. A second came 10 min later when the pump was shut down for a “sheen” test, yet the well continued to flow instead of stopping and drill pipe pressure also increased unexpectedly. Then, 18 min before the explosion, abnormal pressures and mud returns were observed and the pump was abruptly shut down.
“The data suggest that the crew may have attempted mechanical interventions at that point to control the pressure, but soon after, the flow out and pressure increased dramatically and the explosion took place,” the memo said.
The company’s preliminary findings indicate that there were other events in the 24 hr before the accident which merit further inquiry, it added. “As early as 5:05 p.m., almost 5 hr before the explosion, an unexpected loss of fluid was observed in the riser pipe, suggesting that there were leaks in the annular preventer in the [blowout preventer],” it said.
Excess liquid gain
Then, 2 hr before the explosion, during efforts to begin negative pressure testing, the system gained 15 bbl of liquid instead of the 5 bbl that were expected, leading to the possibility that there was an influx from the well, the memo said. It said that BP’s preliminary investigation learned from a cementer witness that the “well continue to flow and spurted.”
Having received an unacceptable result from conducting the negative pressure test through the drill pipe, the pressure test was then moved to the kill line where a volume of fluid came out when the line was opened, BP told the committee’s staff. The line was opened at this point and pressure on the kill line was bled to 0 psi, while pressure on the drill pipe remained at 1,400 psi.
BP’s investigator indicated that a “fundamental mistake” may have been made here because this was an “indicator of a very large abnormality,” the House committee memo said. The kill line then was monitored and by 7:55 p.m., the rig team was “satisfied that [the] test [was] successful,” it continued. At that time, the rig started displacing the remaining fluids with seawater, which led to the three flow indicators described previously.
The memo noted that BP identified several concerns related to the well’s cementing process. “Cement work that was supposed to hold back hydrocarbons failed, allowing the hydrocarbons into the well bore,” it said. “The float collar used in the cementing process did not initially operate as intended and required nine attempts with higher than usual pressures to function properly. Moreover, the float test performed after cementing may not have been definitive, leading to concern that there may have been contamination of the cement due to density differences between the cement and the drilling mud.”
Key questions also exist about whether proper procedures were followed for critical activities throughout the day, the memo continued. Negative pressure testing occurred initially on the drill pipe instead of the kill line, where the drilling plan specified it should take place. The testing eventually moved to the kill line where it was ultimately accepted following anomalous results on the drill pipe, it said.
Evidence also suggests that spacer fluid used as seawater displaced drilling fluid did not rise above the BOP to the level required by the drilling plan, according to the memo. “This increased pressure in the drill pipe may have interfered with later pressure testing,” it suggested.
In addition, the method of displacing the drilling mud with seawater may have interfered with monitoring flow levels from the well because the mud was transferred to another boat instead of being measured in the mud pits, the memo said. “Moreover, mud loggers were not informed when the offloading of drilling mud to the other boat was stopped,” it said.
BP’s initial investigation identified several concerns about the BOP, including the failure of its emergency disconnect system (EDS), its automated mode function (or deadman switch), its shearing function, and remote operated vehicle interventions, the memo said. “The BP investigation has also raised concerns about the maintenance history, modification, inspection, and testing of the BOP,” it said.
Contact Nick Snow at firstname.lastname@example.org.