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24 comments on More on Rig Damage and Structural Integrity

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Engineer-Poet on October 1, 2005 - 2:41am Permalink | Subthread | Comments top
The question on my mind:

How big does the threat from wind and waves have to be before it pays to design e.g. production platforms as submersibles rather than floating?  If something is already below the water, it can't get hit by a wave.

Someone must have investigated this already.

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Mad Oilman on October 1, 2005 - 4:16am Permalink | Subthread | Parent | Comments top
That is one of the main reasons subsea production is now so prevalent. They can be tied together and tied back to existing infrastructure.

In the deepwater, they need to be tied back to a floater for processing and pipeline maintence. Deepwater sea temperatures are damn cold. They cause all kinds of pipeline flow issues. And shut them down. Flow assurance is now a science and there is a ton of active work ongoing to lower the costs for these operations. Currently methanol or ethylene glycol injections into the pipleines are required to ensure flow. This adds to the complexity and expense of the project.

There's also a ton of research being done in subsea separation (get rid of solids and water at the seafloor, eliminating pipeline capacity to carry it all), subsea elecric transmission (to power subsea pumps and equipment) and artificial islands (subsea floating platforms ro reduce sea state risk, but also to lower drilling costs (1st or 2nd gen semi to drill instead of a 4th or 5th).

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Engineer-Poet on October 1, 2005 - 2:01pm Permalink | Subthread | Parent | Comments top
When I look at pictures of those production platforms, I see lots of things that look like cooling towers.  Looks like there's considerable need for cooling aboard those things.  Would sitting down in the deepwater be good for some of the processing?

I was actually thinking of an arrangement where the equipment would be mounted in something like a submarine hull, which could be taken down to a safe depth when storms threatened.  The hull could be filled with air at near-ambient pressure when at depth (obviously with no one aboard) so it would not have to be built to withstand crushing.  If it was only taken deep for protection, it would not need to be designed to operate while deep and pressurized, just to protect itself (e.g. chambers and pipes holding low-pressure gas would have to resist crushing).  300 feet should be deep enough to handle 100-foot waves.

There's got to be a point where submersibility is cheaper than building to resist storm loads.  The question is where.

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wkwillis on October 1, 2005 - 2:42pm Permalink | Subthread | Parent | Comments top
There are internal waves in the ocean on the border between the cold and warm layers of the ocean, but once you get below that it's calmer. The ocean is still a difficult place to work underwater.
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ChrisPhoenix on October 1, 2005 - 6:16pm Permalink | Subthread | Parent | Comments top
If you're handling 100-foot waves, then you're handling (at least) 3 atm of pressure differential. Over the surface area of an oil platform, that's pretty huge.

Chris

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Engineer-Poet on October 1, 2005 - 8:17pm Permalink | Subthread | Parent | Comments top
If you're 300 feet below the average of those 100-foot waves, your pressure differences are going to be quite a bit smaller; IIRC the pressure waves average out and the water motions get less as you go deeper.
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24 comments on More on Rig Damage and Structural Integrity

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