Just saw this little bit of info I hadn't seen before:
Cement plug 12,150 ft SCMT logging tool SCMT (Slim Cement Mapping Tool) Schlumberger Partial CBL done. http://energycommerce.house.gov/documents/20100530/BP-HZN-CEC018441.pdf
Looks like Schlumberger did attempt to run a CBL, but stuck it. Don't know if they attempted to fish for it, push it to bottom or leave it there.
Looks like they did not attempt another CBL run and decided to set the plug higher. Would be interesting to see what they could have hung up on or for that matter what the CBL log they did get looks like.
What depth did they stick the tool? It is possible there was gas/oil working through the plug while it set, which would explain a few things.
First, the channel(s) through the plug would explain the volume increase while they were pumping, and the flow, as the formation pushed fluid through the plug (no integrity).
It would also explain the bad negative pressure test.
And it might explain the changing production estimates, as the plug erodes, with the production from the wellbore increasing steadily. (As opposed to BP “lying” as so many seem to believe).
I can’t really see why an oil company, already with their ‘green’ reputation in shambles, would purposefully under-engineer any oil recovery device. Lost oil is not only a liability, but lost revenue as well, so you would think they would engineer any containment and recovery system for the wellhead for as much (or more than) flow as they expected.
An eroding plug downhole would be like opening a variable choke, exerting steadily diminishing pressure against the fluid coming out of the producing formation, allowing the flow from the well to increase over time.
If the CBL stuck or encountered resistance above the plug, there may have been some of the cement carried uphole by the formation fluid, or the volume of the plug was not calculated correctly (usually there is some small error).