Stability of the Deepwater Horizon

The Deepwater Horizon was a semisubmersible Mobile Offshore Drilling Unit. Officially, it was a Reading and Bates Falcon RBS-8D design. It was constructed in 2001 by Hyundai. The Deepwater Horizon was lost with 11 of her crew on 20 April 2010 in the Gulf of Mexico, when a well known as Macondo 232 blew out and exploded in the course of an operation known as temporary abandonment.

The design of the Deepwater Horizon appears to be very close to that of the Deepwater Nautilus, which is currently in service. The principle difference is that the Nautilus is 8 point moored and the Horizon was dynamically positioned.

The Nautilus design is listed as RBS-8D and the vessel was also built by Hyundai, one year earlier. The Horizon was 4 feet shorter and 52 feet narrower than the Nautilus, displaced 8816 short tons vs. 9700 for the Nautilus, and was powered by 6x9775 hp engines vs the 4x6300 hp on the Nautilus. The similarities between the two vessels leads to the conjecture that the Horizon was an adaptation of the Nautilus design, with dynamic positioning replacing mooring as a station-keeping method.

Both vessels were equipped with large (150 foot boom) cranes as shown by the arrows in the attached photograph of the Horizon.

There is extensive evidence that operation of these cranes on the Horizon caused vessel motion which in turn interfered with two of the three measurements that are essential for well control: pit volume and flow out during circulation. Drill crews, when faced with anomalous readings while crane operations were underway, would order the cranes to be housed until the vessel stabilized. There is no evidence that interference with measurements contributed to the loss of the Horizon, but it is an interesting point when considering the systems characteristics of dynamically positioned semisubmersibles.

It seems, to my layman's eye, that a dynamically positioned rig would have less initial stability than one that had 8 heavy mooring cables hanging off it, but I would definitely like to hear expert opinions on this matter.

Cheers,

Earl

 

Can you please provide this evidence?

Why so?..and please define "initial stability".

 

Evidence:

From the deposition of Craig Breland, crane operator on the Deepwater Horizon:

20 Q. Okay. In your experience, have
21 there been situations with this ceased --
22 where anyone on the rig ceased crane
23 operations because there was a -- they were
24 entering a critical well monitoring phase?
25 A. Yes.
00018:01 Q. Okay. Was -- tell me when those
02 situations have occurred in the past.
03 A. If you're either losing mud flow
04 or gaining mud flow back and they're trying
05 to monitor the pits, the mud pits, they'll
06 stop it because when the crane swings left
07 or right, over the rig, or back on to it,
08 the rig will shift and they can't get
09 accurate measurements in the pits.
10 Q. Now, what rigs have you worked
11 on where they have told you to cease
12 operations because they're trying to
13 monitor the pits?
14 A. The RATHER, the MARIANAS, the
15 AMIRANTE. And I can't remember if we did
16 it on the GOODRICH, but most every rig that
17 I have been on.

From the deposition of Murray Sepulvado, one of the Well Site Leaders ("Company Men) on the Deepwater Horizon:


00126:25 Q. With respect to some of the
00127:01 issues that -- that you've had on this
02 particular well, one of them was the
03 March 8th kick; is that true?
04 A. That's right.
05 Q. Tell me -- tell me what you
06 recall about that.
07 A. The March 8th kick, we were
08 drilling. We had a slow increase in flow
09 volume. The driller called it after about
10 a 34-barrel gain over a 20-minute time
11 frame.
12 It's -- on the floaters,
13 it's hard to pick up a kick of that nature,
14 'cause when they're -- the crane moves,
15 we're floating. If the crane swings
16 around, we could have 10- or 15-barrel
17 pivot in the pits.
18 So to pick up a real slow
19 kick -- kick -- while there's other
20 activity going on in the crane, it's real
21 hard to pick up a -- a very minor increase.
22 So whenever he noticed that
23 the increase was continuos, he had the
24 crane cradle the boom at that level of the
25 rig where we could watch it a few more
00128:01 minutes. And it showed that the well
02 was -- had higher flow rate than normal.

And:

10 Q. Okay. And as I understood your
11 testimony, you said that there were some
12 activities going on the rig at the time
13 with the cranes?
14 A. Yes.
15 Q. And someone made the call to
16 stop the crane activities in order to
17 monitor the well?
18 A. Right. When the mudlogger and
19 the driller started talking, seeing these
20 increase in pits and slight increase in
21 flow, there was crane activity on the rig
22 at the time.
23 Q. Uh-huh.
24 A. So the driller called the crane
25 operator, parked the cranes in the cradle
00356:01 so that everything would level out so we
02 could see what was going on.

These depositions were given in the course of the BP trial. As for "initial stability," that was a poor choice of words. I was trying to describe resistance to being moved from a low or zero angle of heel. And as far as why, it seemed intuitive, but my intuition has been wrong plenty of times before, which is why I asked

Cheers,

Earl

 

Earl

This is not evidence. This is hearsay or a personal account. Evidence requires quantitative independent facts by a recognised authority.

That depends upon many factors, none of which can be inferred from a picture.

 

Well, if you dig into this event, the sad fact is that personal accounts are almost all the evidence there is. If that's not enough, then so be it :-(

As for factors, the picture was included just to give people an idea of where the cranes were located. The vessel itself is extensively documented in the various official inquiries.

Cheers,

Earl

 

Earl

I hear what you’re trying to say.

However, there should be plenty of evidence of “something”. For example, the operating manual and stability book of the rig. That defines everything. Then when was the last time a full survey was done and has there been any modifications to the rig post launching..if so, is this documented and a new lightship and LCG/VCG established…so on and so forth. Any changed that has been requested would have 1) a paper trail and 2) signed off by the relevant technical authorities in both design and Class/Flag authority. There are, or should be, sufficient checks and balances in the whole process to ensure such rigs are “safe”.

Thus the only error is human error….as always. Which is often attributed to “operating manual says one must do XX when YY occurs”..was it done? If not why not and was it reported to anyone?

And part of that is the operating culture of the company. Have they been audited to ensure the whole company from the person that sweeps the floor to the CEO understand their roles their responsibilities and ensures that the chain of command is maintained and everyone is updated when something new has been added or changed or a general industry wide up date. And is this documented?

These are basic fundamentals.

There have been 3 major accidents in the UK for example, where corporate culture and management systems in place lead to such events. These have all now been corrected (still not perfect). Sadly legislation is always reactive never proactive. An accident is required first before something changes.:

http://en.wikipedia.org/wiki/Piper_Alpha
http://en.wikipedia.org/wiki/MS_Herald_of_Free_Enterprise
http://en.wikipedia.org/wiki/Marchioness_disaster

The three cited above, for basic info.

 

Thanks. I've been studying this incident from a systems engineering perspective for a little more than two years and found an industry that focuses on component engineering a lot and systems engineering hardly at all. So I would not be surprised if the adaptation of the Nautilus design did not take into account the effect (if any) of moving from moored to dynamic positioning on drilling operations. The gap between the drilling culture and the marine is huge. This was (sort of OK) when the job of the marine side was to tow an anchored or jackup rig to position and then go home. The transition to a vessel which is under way but not making way has implications that are not yet fully understood.

As far as the corporate and management culture is concerned, discussion would be off topic for this thread, but let's just say it's currently the subject of a two-phase trial (the first phase just ended) in which tens of billions of dollars are at stake, and it's not a pretty sight. There are threads hundreds of postings long on the Drillingclub and gCaptain forums on these issues.

But I don't want to get off on that tangent. My interest is in whether the original designers missed a systems-level interaction and introduced a risk factor without knowing it.

Cheers,

Earl

 

Even more so between the differnces in opertaion of such rigs between the US and EU. Which Im sure will come out in such trails/debates.

Without know the original design SOR and whether a proper HAZOPS study was done for implementation and what effects, if any, were mitigated and whether this was properly documented and validate by retesting, how is anyone to know?

 

Neither and SOR nor a HAZOPS study has surfaced in the multiple corporate or government investigations of the incident. Given the history of the vessel (three owners, two flags of convenience) it's possible that if they existed they have been lost. If a HAZOPS study was done (which I personally doubt, given the way that industry builds things) it certainly failed to mitigate at least one substantial risk factor.

It just seems strange to me that we can't even speculate on whether there is a difference between two highly similar vessels, one moored and one free-floating, in the area of reaction to crane operations. If speculation is all we have, that's all right provided it is clearly labelled as such in any narrative. If there isn't even enough to speculate on, well, that's an answer too

Cheers,

Earl

 

Question: What water depth did the Nautilus operate in?

Agreed.

In 2008 I observed the DH with a large list angle resulting from some sort of malfunction/mistake. In this position, the crew was offloaded onto the MV C-Freedom using a large crane + the personnel basket. I believe the word "Liebhart" was painted on the crane.

 

Deepwater Nautilus is rated for a maximum water depth of 8000 feet. The spec sheet for the DH names the cranes as "Liebherr," rated 80 metric tons @ 35 feet.

If you'd like, I can dig into the files and find the official cause of the listing incident, I just don't recall it right now.

Cheers,

Earl

 

The only conclusion I can draw from that statement is that there is either a cover up or pure gross negligence in the management system.

Since there will always be paperwork. How else are things designed order fabricated built, surveyed and "approved"?? Did Joe Bloggs walk down the road, open his coat at the side and say..."wanna buy a rig, cash in hand no questions asked", in soft low voice??

 

The only "incident" in the 2008 episode was that they were able to right it after evacuating the crew.

It was some sort of ballasting problem, I just don't know if it was due to human error or equipment malfunction, or some strange amalgam of the two. I am starting to feel infuriated thinking about reading any official documents related to the platform, but, the curious engineer part of me is morbidly curious.

 

@ 35 feet? What does that measurement mean/reference? I'm not familiar with heavy lift crane specs. The biggest number I recall seeing was "70,000lb" written in chalk on a structural component that I believe belonged to Halliburton and it looked like an A-frame and was lifted directly by one of the "Liebherr" cranes from the OSV.

 

On land based cranes the nameplate rating is the maximum SWL with no fly jib (extension), and the boom luffed back to its steepest angle and therefore smallest radius (overturning moment). Based on that logic I would imagine 35' is the radius from the crane centre line to the hook measured horizontally..... Assuming the same applies at sea.