National Incident Commander Thad Allen said today scientists are reviewing how to proceed after determining about 1,000 barrels of oil is trapped in the Macondo well by a cement plug poured from the top last week.
Injecting mud and cement from the bottom of the well, as originally planned, may force oil out the top and wreck the bottom seal, creating a new route to the surface for oil and gas, Allen said. Pressure tests of the static kill indicate that the cement plugged the well’s central core, or production casing, then flowed into the oil reservoir and back up to plug the annulus, a space between the production casing and the outer casing that runs all the way to the top of the well.
“How thick the cement barrier is between the annulus and the reservoir, we just don’t know,” Allen said. “It might be very thin, and we go and put pressure on that and we have a problem.”
By proceeding with the static kill and plugging the well from the top with 500 barrels of hard-set cement the relief well plug will not be as secure as originally planed. Had the mud been left in place (without cementing), then pushing it up and out with cement pumped in from the bottom through the relief well would have been a better way to proceed, experts said.
Scientists continued to look through data to see if they had already sealed the well off permanently with cement.
Allen warned that there was a small chance that cement pumped in during the static kill had travelled down to the reservoir and then back up in the outer casing, sealing the well from both ends.
Pumping more cement and mud in from the relief well could raise the pressure to dangerous levels, Allen said. But if BP and Allen do decide to go ahead, drilling on the relief wells will resume on Sunday, with the final kill complete in about four days.