BP Plc will get the go-ahead to finish a relief well to finally seal its blown-out oil well but is doing a last batch of testing and planning first, the top government official overseeing the Gulf of Mexico oil spill said on Saturday.
The final go-ahead could come by Tuesday, and it could take another 96 hours or four days to intercept the bottom of the damaged Macondo well and begin cementing it, retired Coast Guard Admiral Thad Allen told a teleconference.
The relief well as of Saturday was within 50 feet (15.24 metres) of the bottom of Macondo and 3.5 feet (1 metre) to the side of it, Allen said.
"We will kill the well. The relief well will be executed and the bottom kill will be executed," Allen said. "It's just a matter of finishing up tests so we understand the conditions under which we should move forward and precautions that may be taken to mitigate risk."
Allen said the last round of testing and planning is aimed at accurately predicting and preparing to control well pressures that could build up during the "bottom-kill" process.
The concern is to prevent oil from escaping into the water during the bottom-kill. Estimates are as much as 1,000 barrels of oil could be trapped in the well bore as a result of the earlier cementing done from the top.
"What we've directed them to do is to give us a plan on how they would control that pressure ... how they would mitigate it, and that's one of the things they're going to be providing us," Allen said.
Final preparation could involve removing the current blowout preventer stack atop the well and replacing it with a "BOP" better able to withstand anticipated bottom-kill pressures, Allen said.
That would add another step to the final process of sealing the well from the bottom, but the replacement BOP is already on the sea bottom atop the backup relief well that is being drilled, he said.
If final bottom-killing of the well goes forward with the current blowout preventer, Allen said he wants BP to prepare extra measures - perhaps venting - to deal with excessive pressures should they occur.