According to National Incident Commander Thad Allen, the two possible reasons that are being discussed regarding what is blocking the annulus are:
- During the cementing phase of the static kill, cement went down the length of the 13,000+ foot well, made a u-turn back up into the annulus, hardening in place.
- There has been "a collapse in the formation" around the Macondo well.
Press Briefing by National Incident Commander Thad Allen, August 19, 2010 at 12:00 p.m. EDT:
"5,000 feet of cement... was put in during the top kill."
"There's about 5,000 feet of cement there."
"Well there's some that would tell you that the lack of communication between the annulus and the reservoir might not be cement, it could be just a collapse of the formation around it."
Why is a compromised formation a bad thing? See: