The memo details several troubling signs of improper well functioning in the hour before the April 20 blast on the rig that BP leased from owner-operator Transocean Ltd. The accident killed 11 workers.
The memo notes, for instance, that 41 minutes before the blast, a well pump was shut down for a test, “yet the well continued to flow instead of stopping and drill pipe pressure also unexpectedly increased.” It adds that 18 minutes before the blast, abnormal pressures were observed and the pump was shut down.
“The data suggests 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 states.
The committee memo also notes signs of problems in the 24 hours before the blast. For instance, five hours before the explosion, there was an “unexpected loss of fluid” in the well’s riser pipe, which suggests leaks in the blowout prevention device.
In addition, the memo describes BP’s concerns with cementing work on the well, which was conducted by oil-services company Halliburton (which, for its part, has maintained that it followed BP’s instructions on the project).
“Cement work that was supposed to hold back hydrocarbons failed, allowing the hydrocarbons into the well bore. 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,” the memo states.
Elsewhere, the memo describes BP’s concerns about the well’s blowout preventer, referred to as a BOP, which is supposed to be a failsafe device but did not deploy properly.
The concerns include “failure of its emergency disconnect system (EDS), the failure of its automated mode function or deadman switch, the failure of the BOP’s shearing functions, and the failure of the remote operated vehicle interventions.”
“The BP investigation has also raised concerns about the maintenance history, modification, inspection and testing of the BOP,” it states.