Previously, he had predicted that the relief well would be completed this week. Initially this week he declined to set a firm date. On Thursday, Allen said the new instruction would push back the date to sometime after Sept. 6.
"We do not want to have damage to the blowout preventer," he said in explaining the delay. "We are concerned about preserving evidence."
Why the blowout preventer - a giant collection of valves designed to sever a deepwater well's drilling pipe in the event of an emergency - did not work has been a key question for investigators probing the April 20 explosion that killed 11 oil-rig workers and sparked a gusher that caused billions of dollars in economic damage along the Gulf Coast.
Other questions
BP officials told Congress in May that diagrams they had of the blowout preventer were inaccurate and that they wasted days trying to activate its shearing mechanisms.
Other reports have raised questions about the way the device was modified and maintained, including a failure to repair a hydraulic leak that may have undermined its ability to shear through the drill pipe.
The blowout preventer actually is owned by Transocean, the company from which BP had leased the Deepwater Horizon drilling rig. BP and Transocean have blamed each other for the device's failure to seal the well, and the two appear likely to face off in court over how much each should pay out for the tragedy.
In a sternly worded letter to BP's lawyers, Transocean has accused the oil giant of withholding documents key to pinpointing the cause of the accident, the Associated Press reported.
BP spokeswoman Elizabeth Ashford said Transocean's accusations were misleading and misguided.
