What would it take to avoid sinking the platform? 2

[docellen]

Seems like just a little extra steel between the underwater pontoons would do it. Then, of course, we would need a tugboat nearby to keep the rig from drifting off and snapping the riser.

 

[waross]

That brings up a question that I have wondered about. Why did the rig sink. Fire damage to the structure? Malfunctioning bouyancy controls as a result of the fire, or was it pulled down by the still connected riser as it drifted off station?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DrillerNic]

I'd be surprised if the marine riser pulled it down, as the rig (not a platform by the way- a platform stands on the seabed) usually supports it. And don't forget, docellen, that the Deepwater Horizon was a dynamically postioned rig (no anchors) - so you wouldn't need a tugboat to keep it on station, just larger thrusters on the DP system.

I'd suggest the most likely reason it sank is that a massive fire that lasted for about 3 days resulted in a loss of structural integrity?

 

[waross]

Thanks Nic. The reason I suggested the riser is that I understand that the riser never disconnected as it was supposed to. Was the fire fed by fuel already present on the rig or did the riser feed the fire right to the end?
Was any power restored, or were the generators still out and the rig drifting for three days?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[docellen]

The fire would burn out quickly without continuous feed from the riser. Even if all the steel melted, the underwater pontoons should still be floating. I'm wondering if the fire fighters made a colossal mistake, and deliberately sank it. Maybe in all the confusion, they didn't think to ask if sinking it would be a good idea. It wouldn't take 3 days for the steel to get hot.

I sure wish BP would be more open with technical information.

 

[BigInch]

Too much firewater tends to destroy positive buoyancy.

"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.liv

 

[docellen]

But how does that water get inside the pontoons. I suppose it is remotely possible a piece of steel fell like an arrow and penetrated the pontoon underwater. Maybe with one pontoon out, the entire rig would sink.

 

[CH5OH]

the rig got flooded,the pontoons are designed to give the rig enough buyoncy, its not designed to fill the rig up with water.

 

[waross]

This is not the first vessel to be sunk by to much fire fighting water. Did no one figure this out or was the sinking intentional.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DrillerNic]

Oil rig fires can get pretty hot- hot enough for steel to loose it's integrity (not to melt- just loose enough strength that the structure collapses). Look at what was remained of the Piper afer it had burnt for a day- only the wellhead module (held up by 24 wells) was left...

 

[docellen]

How about adding a diverter at the top of the riser to keep the oil and gas shooting in a safe direction, away from the rig? Maybe even put this underwater, so there is very little chance of the fire even starting.

 

[waross]

In normal operation the riser must allow the free flow of the return mud.
The fire probably started when the mixtuire of methane gas and air ignited. The military would call this a "fuel-air bomb".
Two possible issues with an underwater discharge.
This may lead to an enormous buildup of a methane-air mix that may eventually reach the rig and explode. It has been stated that the larges explosions possible short of neuclear are air-fuel mixes. The largest peacetime explosion in Europe was a fuel air explosion resulting from gasoline vapours when a fuel storage tank overflowed, and the spilling gasoline mixed with air. Ironically, it may have been ignited by a spark from the fire alarm system.
An underwater diversion would probably require some type of control or valving so that the mud could return in normal operation.
I suggest that rather than major modifications to the BOP design, (so it won't shear a drill stem joint? In a functioning BOP there are two shears positioned so that joints are not able to obstruct both at the same time.) The drilling culture of some companies must be changed so that work follows best practice and safety equipment is maintained in operating order at all times.
In addition, it is starting to look as if the failure of the BOP may have averted a worse environmental disaster. I understand that there is now reluctance to stop the flow for fear that the casing may rupture below the sea floor and release even greater amounts of oil at random locations. There have been suggestions that this may have already happened and restricting the flow at the BOP will make this situation worse.
An analogy;
In North America, large transport trucks have an emergency braking and parking system that is applied by springs and released by air pressure. If an air line breaks in this system the brakes are applied automatically. It is possible to release these brakes manually so that the rig may be moved for short distances, eg; off the highway. It is illegal to drive on the highway with this system disabled, even though the service brakes will still work normally.
If there is a broken line in the trailer brake system, the trailer brakes will be applied automatically with reservoir pressure, and should this fail the spring brakes will apply automatically. The trailer reservoirs may be exhausted and the system isolated and the spring brakes "Cranked off" and the rig may be moved and stopped with the truck service brakes. At this point, the braking force may be less than half of normal. But the truck is still capable of being driven at normal speeds, it just doesn't stop very well.
Now suppose that the driver of a "Super B train" (Two trailers has a problem with his trailer brakes and disables them. He had brakes on 14 dual tired wheels. Now he has brakes on only 4 dual tired wheels. His initial braking force will be 4/14 or 29%. A panic stop from highway speed mayquickly overheat the remaining brakes and result in less than 10% of normal breaking force.
Now, if a driver has problems on the road and, in order to save time, disables his trailer brakes and drives at normal speed and then has a horrendous wreck, do we blame the driver and possibly his supervisor, or do we redesign the braking systems of all the trucks in North America?
Wouldn't happen? Look at the accident reports for brake failures due to simple neglect in the mountains of Western Canada.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[docellen]

The diverter I'm thinking of wouldn't require redesign of all trucks in North America. In fact it would hardly cost anything, compared to the cost of a BOP. It wouldn't be 100% effective. If there is no wind, the gas could still accumulate around the rig. Still, I would rather have this than nothing. Remember it is a backup system. The main line of defense should be early detection of a kick.

The more I learn about this disaster, the more I am convinced that some simple, low-cost engineering will greatly improve safety. Have you ever been in a missile silo? It takes two guys with keys, standing at opposite ends of the room, or the missile won't launch. I can imagine a system that not only has automatic shutoff when the mud flow is imbalanced, but requires two guys with their hands on the controls to keep the auto shutoff from activating.

Safety culture is important. Engineering can make it easy.

 

[waross]

The point that I am trying to make is that this is not so much an equipment failure as a human failure on the part of bp.
You could have 12 people holding buttons to hold off the safeties. When one of them decides to activate, it doesn't matter if the annular seal won't work because it was damaged and not repaired. It doesn't matter if the second annular seal has been turned off. It doesn't matter if there is not enough hydraulic pressure to activate the rams.
I imagine that it may be time to consider designing shears that are tough enough to shear a coupling, but that still won't help is there is a hydraulic leak and the system has been turned off.
This is not a hardware problem. It is a people problem.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[docellen]

I agree, the problems leading to the current disaster are mostly human failures, but I just wouldn't go so far as to say it is not at all a problem that engineers can help fix. There are plenty of things we can do to improve the design. To use your examples, damaged seals, low hydraulic pressure, etc., how about we add a data logging device, like many cars have now, that records the results of regular testing on the BOP. If any of the above problems were to occur, it would show up as a record of excessive flow during a pressure test. How about we add a computer interface, so inspectors can query the data any time the have doubts that a test was done.

Yes, I know, clever humans could figure out a way to disable the recorder, but that is a lot less likely than the current "failure mode", where people just forget to do any tests.

 

[DrillerNic]

Docellen- a diverter is commonly used on floating rigs while you are drilling surface hole, before the BOP is estabilished (you have to get to a certain depth to provide a strong enough foundation for the BOP).

A diverter is typically a 3000psi rated annular and immeditely below it the riser has two side outlets with interlocked valves on each. These side outlets go overboard to each side of the rig. The diverter actuated, and the annular closes and one of the side outlet valves is opened to divert any flow to the downwide side of the platform, hopefully giving everyone enough time to get to muster and get off the rig.

A diverter is the defence against "shallow gas" thin, isolated pockets of gas in the top 500ft or so of sediment. Shallow gas scares the shit out of the offshore drilling industry because it is so dangerous- as well as the fact that there isn't a BOP, there's also the issue of loss of bouyancy due to the gas in the water column- there's a famous and terrifying video clip of (I think) the Sedco 711 fractically trying to get off station while the sea 'boils' around it... you can see the entire rig listing badly as it looses bouyancy on one side. The issue of loss of bouyancy is the main resistance to the idea of subsea diverters (which have been suggested).

So, traditionally, once the subsea BOP was on the wellhead and tested, everything was OK, as the BOP would always work- 100% redundancy on the separate rams and annulars, 100% redundancy on the control systems, and then 100% redundancy on the emergency control systems (when I started drilling 15 years ago emergency BOP control systems weren't really known). This is what everyone I talk in drilling to wants to know: why did the Deepwater Horizon's BOP fail????

A diverter as well as the BOP might become law; but remember that everyone except the guys on the drill floor and pump room got off the Deepwater Express, and that the gas bubble would still have arrived at the surface if the rig had had a diverter as well as the subsea BOP (they didn't shut the well in when there were indications that the well was starting to flow 20 mins before the explosion, so I doubt they would have shut a diverter either). Finding out why the gas exploded when everything is supposed to be EXd zone rated would be a better solution.

I was chatting about this to a guy who is now an OIM on a North Sea platform (I wont't say which one) and he said that in the 80's this platform had a gas leak: 3,000,000scf. The only thing that stopped it being a second Piper was the gas was above the Upper Explosion Limit, and the production techs had enough time to cut off all electrical power to the entire platform. In the internal investigation afterwards, they realised that almost all the lighting in the accomdation block and even some of the lighting outside in the drilling and production modules was just bare wire connections.....

 

[docellen]

I sure wish we had a diagram of the BOP. That would answer a lot of questions about redundancy. My guess is there is some common factor, like a single hydraulic supply that got low on pressure, due to a slow leak that was ignored. That would explain why all the rams seem to be working, holding off some pressure at each ram, but none are fully closed.

BP has released a detailed diagram of the externals (see

http://energy.gov/open/oilspilldata.htm)

but that doesn't help with questions about the hydraulics, redundant connectors, etc.

I can't find any diagram of a diverter. Seems to me it should be entirely passive, not requiring anything to be actuated.

Finding the exact cause of the BOP failure may take months. I think we already know enough, however, to move ahead with fixing the human-factor problems, and improving the design of the wellhead, BOP, and rig. The improvements I have on my list could be done even before all the investigations are finished.

 

[CH5OH]

docellen,I contacted BP requesting detailed drawings of the BOP.their answer:thank you for your questions,blablabla..., we do not have time to answer them
my conclusion:
main reason to establish communication between BP and public is not to provide or to get information but to polish
BP's image towards the public

 

[docellen]

Perhaps someone on this forum has access to a manual, or knows someone who does.

 

[JRMacGregor]

To answer the original question - there IS steel between the pontoons to hold the rig together as well as the deck. These and the deck box are what keeps the two pontoons together.

Although hot fires like this can weaken the steel (like the derrick, for example) it does not seem the immediate reason for the sinking. Her deck box did not seem to fall apart and then the rig sink.

The final moments of the rig on the surface did seem to include noises of structural failure. But by that stage she was laying over at a considerable angle and low in the water. That angle could have helped things start to break loose.

The only way she got into that attitude was because she lost buoyancy or there was more water/oil in her than at the start of the incident. The latter could have happened for one or two reasons;

1) oil or water or both finding their way down into the rig columns or pontoons (or even into the deck box). This should not normally happen for the same reason the rig does not fill up in heavy rain. But the explosions probably opened up paths into the previously water/weathertight structure. In fact, oil/water gathering in the deck box would be worse for stability than oil water running below into the pontoons/columns.

2) ballast flooding into previously empty tanks because of ballast valves opened to the sea by destroyed ballast control system (SHOULD not happen due to fail safe ship side valves, but who knows what was actually installed)