Stability of the Deepwater Horizon

Thank you for the pithy explanation (I actually understand, imagine that).

So, I'm still morbidly curious, what was the "official cause" of the 2008 incident?

 

Technically no. As I understand it they (the oil companies) don't buy the rig, they lease/rent it. Instead of a rental car, it's a rental rig! The cost is somewhat high though, I believe to the tune of ~$400,000-$500,000 per day.

 

Indeed.
Thus was it a back door shady deal, or, like a car rental, is there paper work and showing the price what was being rented etc etc.....all smells a bit fishy to me.

 

Might all depend on one's perceptions. One could say, for example, its very existence was a 'shady deal,' but not due to lack of paperwork and documentation, in a culture embued with the love of paperwork and documentation.

I read somewhere that the Deepwater Horizon capsized when it sank and is on the ocean bottom upside-down about 1500ft away from the wellhead. I wonder if there's any photographs of it on the seabed?

 

I don't quite understand why we're off on this tangent, but I do feel I owe you the courtesy of a reply, so here goes

WRT the SOR and other documentation in support of the design: The Horizon was designed in-house by an operating company called Reading and Bates. Other than what may or may not have been submitted to her first Flag State (Panama) these would be internal R&B documents. R&B was acquired by Global Santa Fe, who in turn was acquired by Transocean. Any documentation that survived these transitions would probably be locked up somewhere in Switzerland. Transocean is currently under attack by a corporate raider as well as being sued by practically every government and business entity on the Gulf Coast, and isn't saying anything to anybody except under duress. They lost their attempt to prevent the Chemical Safety Board from investigating the accident and so may be forced to release what they have but I'm not holding my breath.

WRT to the definition of evidence: there is no authority with oversight that spans both the drilling and marine sides, and who would be testing for adverse interactions between the two. At the level of the Flag State at the time of the incident (Marshall Islands) the oversight was so lax the vessel was registered as moored rather than dynamically positioned, an error which was not discovered until after she sank. Inspections were subcontracted to two classification societies, one for drilling and one for marine, and there was no coordination between the two. At the level of the Coastal State (USA) the regulatory structures for drilling and marine do not come together until the President's Cabinet (Secretary of Interior and Secretary of Homeland Security, who oversees the Coast Guard). At the level of the two corporations involved (BP and Transocean) both exhibit, culturally and organizationally, wide separation between the drilling and marine activities. At the level of the rig itself, the bridge crew had no visibility whatever into the difficulties the drillers were having until a few minutes before the blowout and subsequent explosion.

You may depreciate the testimony of the crew members as you wish, but the third quote was from the sworn testimony of a gentleman who spent 30 years drilling substantially over 100 offshore wells. I seriously doubt he was hallucinating every time he witnessed pit volume fluctuations and rig movement when crane operations were underway, and cessation of same when those operations were halted. Also, the telemetry from the Horizon in the hours before the blowout shows pit volume fluctuations during the time crew members have testified crane operations were going on. These items may not meet your standard of evidence but I think many people would agree with me that they suggest my question is not frivolous.

Which gets me back to that question: If one has two nearly identical semisubmersibles like the Nautilus/Horizon pair, does the fact that one is operated moored and the other operated dynamically positioned make any difference in their respective motions (if any) induced by crane operations?

Cheers,

Earl

 

Ad Hoc is off on another of his quibbling crusades. When I was in Japan and got bored, I usually looked up a woman instead. But hey... different strokes for different folks, I guess.

Testimony from someone about something they directly experienced or witnessed is hardly 'hearsay.'

I can just imagine the court scenes if Ad Hoc's definition became accepted instead....

"Excuse me, sir. But do you have a report from an independent authority verifying that the object you supposedly saw the defendant plunging into the victim's back was indeed a knife -- and that it was indeed capable of actually penetrating said victim's body?"

-Well, I think I think I know a knife when I see one...

"Objection, your honor! This man is not a qualified, impartial expert. Anything he says is simply hearsay evidence, and I demand that it be stricken from the record."


You don't owe him a courteous reply, Earl. In fact, he doesn't deserve one. I made an offhand remark one day about Julia Child living to a ripe old age in spite of cooking with butter, and Ad Hoc hounded me for days demanding to know whether or not I believe butter is 'good.'

 

Find/provide line drawings, lightweights+locs, deadweights+locs, mooring specs w/operating depths and a concise definition of how we're defining 'stability.' As pointed out, accurately, by Mr. Ad Hoc, this isn't an initial stability problem. I have some appropriate definitions in mind but want to hear how others might define 'stability' in this case.

As for catenaries, what do mooring lines add/change/affect? Help me out:
- Adds deadweight down low
- Shipboard tension control?
- Touchdown length increases motion resistance
- Yaw rate damping
- Marine growth on mooring increases mooring line mass/added mass/damping over lifetime of deployment
- Lateral plane hydrodynamic added mass + damping. Resonance?
- Vertical plane hydrodynamic added mass + damping. Resonance?
- Nonlinear/weird forces: galloping/whipping? Anchor drag embedment forces?

It is probably accurate to say that the mooring lines affect both the overall stability (initial vs large angle) as well as its frequency response properties. So, assuming that, is it fair to re-phrase the thesis as: "did the crane swivel motion perturb the system enough to matter?" When I say "system" I think I really mean "rigid body dynamic system" (vs 'marine systems engineering')

 

It was a lockout/tagout failure during maintenance:

In May 2008, DEEPWATER HORIZON suffered flooding in its starboard forward column. ABS conducted an inspection to verify repairs to the damaged equipment. According to the RMI [Republic of the Marshall Islands] Report of Vessel Casualty or Accident submitted by the Master:

“The preliminary cause is during the early morning of 26 May 08 a 12 inch pipe approximately 5 feet long had been removed from the seawater line, which can be crossed over to the ballast system. The pump was electrically isolated, but the valves that protect the pump room from water ingress were not mechanically isolated. Due to lack of communication a valve in the system was opened causing an ingress of water.”

In other words, someone opened a valve that should have remained closed, with an effect similar to cutting a 12 inch hole in the bottom of the MODU. This action most probably resulted from a failure to follow the established procedures for tagging out or securing equipment during maintenance, created a flooding and stability issue that required the evacuation of non-essential personnel to a standby vessel.

To be fair to the crew, fatigue and overwork was probably involved. It has been my experience that every time a company is acquired there is a squeeze by the spreadsheet jockeys to make it appear like the great deal they pitched to management. It is the case that Transocean cut maintenance and engineering staff on the rig after they acquired it. The plaintiff's seaworthiness expert, who obviously had an axe to grind, referred to the state of the vessel as "deplorable."

Earl

 

An extract from the USCG report giving vessel particulars, lo-res line drawings, and a post-sinking analysis can be downloaded from here:

http://bit.ly/ZyaiZf

An extract from the Marshall Islands report, also giving vessel particulars and including a larger set of high-res drawings can be downloaded from here:

http://bit.ly/12XUSyb

That's all the publicly available stuff I've been able to turn up.

Cheers,

Earl

 

Cool, thanks for sharing.

 

We’re not. It is all pertinent to your question.

And therein lies the start of the problems…which is frankly beyond any of us obtaining all the facts if such is the MO of the companies. Clearly this sector works in a totally different way to mine.

You misunderstand me, I’m not, not one bit. But it doesn’t take away that it is still hearsay/personal accounts. Facts, hard evidence, any demonstrated tank test or calculation or detailed analysis with given said assumptions, pre or post HAZOPS/SOR that can be repeated by anyone, are what is required.

CWTeebs has given you a nice starting summary. There is so much more that is required to answer your question fully. But this is the start. If this basic information cannot be obtained, the question is simply why not?

Rather damming conclusions about lack of evidence here too!


Thanks for the link

 

In reviewing the posted material, I note that neither describes the heavy machinery at the top of the derrick. I'm working on getting an estimate now.

Update: my source says that stuff weighs about 70,000 pounds.

Cheers,

Earl

 

Oh dear, I seem to have offended someone. I've received negative rep (anonymous, of course) for the above post, along with this message: "Highly inflammatory and unnecessary towards Ad Hoc."

Apparently the poster has never had to suffer through one of Ad Hoc's irrational attacks - where he seizes on a minor or completely irrelevant part of someone's post, and spends days or weeks pounding it into the ground.

I wasn't kidding or exaggerating when I mentioned the great 'Is Butter Good?!?' controversy. And it left me with a low tolerance for that sort of irrational arguing-for-the-sake-of-arguing behavior.....

 

Sir,

Please stop.

 

Earl

This is a red herring. Just a quick review of the rig, in the doc’s you supplied shows the displacement to be circa 53,000 tonnes. (NOTE: the USCG report incorrectly defines a metric tonne, MT, as a “ton” – this constant throw back to a imperial system of measurements probably is not helping matters).

The crane and reach you supplied gives a moment of roughly 800t.m

If the rig is roughly 53,000 tonne, then the moment lever is just a paltry 0.02m when crane is fully extended i.e. Nothing, as one would expect. The main issue is the VCG in this context, but I suspect the same would be true here too. Since ordinarily on such vessels heavy items would be located at or as close as possible to the operating VCG.