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).
Looked, but couldn't find any info as to depth, reason they stuck it or how much was logged.
Looked at the Schlumberger specs on the tool and found the recommended maximum casing size for it is 7 5/8".
It is also capable of running a production logging package below the sonic:
temp., pressure, gradiomonometer and flowmeter.
Don't know if they ran the whole works.
I know I get hung up on the technical crap, but those tools are your eyes to what the hell is going on with the downhole structures in the well.
Been retired for 12 years so the new stuff is well beyond the equipment I worked on.