They were operating on well-known and understood tight margins on pressure balance ever since the incident during partial drilling by the earlier rig, and right through completion of the drilling to the final “primary” cement job. That balance was always between too little (mud, pressure, cement, etc) failing to control the hazardous hydrocarbons, vs too much (mud, pressure, cement, etc) destroying (the value of) the well. It may seem scary to lay people, but this is always what engineering is about – difficult judgements by responsible, moral people – we’ll “probably” be OK. It looks like “cost-cutting” to do less, but we all cost-cut (look for the best price, the most cost/value effective) every day.
[At this point, I’ve only read as far as the end of the cement design and analysis – ch4, p102 – and I’ve not seen any mentions (yet) of the problems and risks associated with the BOP systems, or the top-sides relief systems, serious but secondary – but I’ll hazard a guess (based on earlier reading of BP’s own report) that the real failure is the decision to ignore the failed negative pressure test (!), and the failure of any warning / criticality signs in BP’s higher supervisory management systems that this whole operation was on tight margins, which could have enforced double checks on the safety-critical decision points, like this one, and other additional quality surveillance. As I said earlier the irony is that BP were one of the first to introduce “criticality” ratings to the industry, 25 years ago.]
So, continuing, reading on … a quote from the commission report (their italic emphasis, not mine) and even with hindsight their use of the tense “would” – is telling.
“At the Macondo well, the negative-pressure test was the only test performed that would have checked the integrity of the bottom-hole cement job.”
And later …
“It was therefore critical to test and confirm the ability of the well (including the primary cement job) to withstand the under-balance.”
The visiting execs and the new trainee in the team both add to the dynamics of dealing with the apparent problem at a critical moment in what was already known to be a critically-balanced situation – interesting. And then the fateful error :
” … the 1,400 psi reading on the drill pipe could only have been caused by a leak into the well. Nevertheless, at 8 pm, BP Well Site Leaders, in consultation with the crew, made a key error and mistakenly concluded the second negative test procedure had confirmed the well’s integrity.”
After that, yes the BOP’s should have been a last line of defence, but weren’t … it’s history … Having been in the pressure testing position myself on several projects, I feel for Anderson …. was he amongst the dead, I wonder ? [He was.]
The recommendations need reading in detail, but this looks like systemic management / surveillance / regulation system needs, so that what look like normal processes in abnormal situations don’t (accidentally) skip critical checks. To their credit, BP still seems to be taking the full hit of responsibility, but I doubt BP is special in this respect. These are industry needs.