how long would deep sea oil rigs last?

[mithril]

i've been thinking about a particular anime mecha roleplaying game, and i had this cool idea of a group operating in the game's more post-apoc like time period and using a deep sea Oil platform, like those in the north sea, as a base of operation for operations against the alien force occupying earth.

then i realized that even if it was something recent like the Troll A platform, any such facility would be 50 years old or older. and the setting doesn't seem likely to support anything built later, since oil becomes a lot less important in the setting. i know a few rigs in the north sea have lasted for over 30 years now, but i also know those have had continuous upkeep, which not all would have in this semi-post-apoc setting.


and looking at pictures of various oil rigs, i'm not sure how well you could adapt them to hold VTOL aircraft/mecha. sure they have a helipad, but few look like they have any kind of storage for helicopters, and most don't really have much open deck either. we are talking Apache/Harrier sized stuff in this setting, mainly.

could an oil platform built in the 90's last that long in a condition safe enough to use as a base?
could one of the platforms be adapted to house and operate VTOL fighters/mecha?

 

[CJGibson]

The one I'm sitting on right now has been here forty years and the field probably has another twenty years life in it.

Depends what you mean by deep sea. Proper deep sea instalations are rare nowadays, mainly being floating production storage and offloading vessels (FPSO) which are tied back to seabed manifolds and once the field is depleted, move away to another location.

Chris

 

[2IDSGT]

@mithril

Most of the individuals who play that sort of game probably don't know/care about the world outside the 4 walls of their mom's basement. So feel free to make the platform as durable/capable as your script demands.

 

[mithril]

was thinking something like the Troll platform linked above, or maybe comparable to the Statfjord platforms. concrete gravity base construction that sits on the ocean floor.

the setting has some alternate history aspects even before aliens and mecha show up (it was originally just set 'in the future', but now we have advanced well past the time of the setting's WW3 and 1st alien invasion), so i can easily fictionalize the specific platform, but i rather liked the idea of a north sea oil platform, since those tend to actually rest on the sea floor, and a good chunk of my other homemade material for this game has focused on the (presently) little detailed areas of europe.

i'm mostly worried about the feasibility of such platforms buil in the 90's lasting to the 2040's without constant maintence, and whether such platforms could actually be a good base. plus tips for depicting such platforms would be helpful. little details that could be worked into descriptions of the enviroment or layout, things people living on such platforms tend to do, etc.

@mithril

Most of the individuals who play that sort of game probably don't know/care about the world outside the 4 walls of their mom's basement. So feel free to make the platform as durable/capable as your script demands.

considering that the games i'm currently in include players who are engineers, scientists, historians, active/retired military personnel, and businessmen in real life, most of which own their own homes and are either in stable relationships or married, i find that not only extremely unhelpful, but downright insulting.

 

[SpudmanWP]

There is more in the ocean than just oil, deep sea mining for starters.

 

[piko1]

the question should be why not if the Rig is on the ocean floor but from what you describe i see it more like Floating airport like the one in Tokyo bay but off shore the rig base would look more like amphibious assault ship or carrier did i take the point

 

[mithril]

actually more like how harriers were operated off the Atlantic Causeway and Atlantic Conveyor. the setting has a mix of helicopters and aircraft that use lift-fan VTOL systems, some of which can convert to humanoid mecha (it is an anime inspired scifi setting..)

i was thinking that an oil platform could use it's helicopter pad as a place to launch and recover VTOL aircraft, and that if space on the platform's deck could be found it could store a couple for rearming and maintenance between missions.

 

[RP1]

Hi there,


I looked at an offshore transhipment hub for an EC consultancy thingy and was quite surprised at just how long a well designed concrete offshore structure can last. DNV have classed the concrete structure of an LNG terminal as having an indefinite life, and Soviet & Russian experience with concrete floating docks (yes, several of them are concrete) have shown them to be exceptionally low maintenance compared to steel - and that pretty much translates to a longer life. We are probably talking about lives of well over a hundred years, if not more for some designs, so 1990-2040 is very short.


Maintenance is only needed if something breaks - and if concrete is artificial rock, so doesn't usually break on its' own. The module on top is another issue, of course.


RP1

 

[mithril]

Maintenance is only needed if something breaks - and if concrete is artificial rock, so doesn't usually break on its' own. The module on top is another issue, of course.

what kind of condition do you think the module on top would be in?

 

[CJGibson]

Knackered!

The legs usually hold risers, pipework and access, teh gravity base is usually storage tanks.

Have a look at Ninian Central, it might suit your scenario. I've not been on it, but watched it being built and did a job nearby a few years ago and it is impressive.

Chris

 

[RP1]

what kind of condition do you think the module on top would be in?

As Chris indicates; not good. Sea water - and the air immediately over the sea - eats metal like you wouldn't believe. The thicker structural members with significant safety margins will probably survive, but will have lost much of their strength. Anything protected by a well applied modern paint system might be in reasonable shape, but even the best system has a lifespan of less than 50 years, so corrosion will have occurred.


The thinner components, and those only protected by conventional paints, greases etc will not fare well. The whole drilling and any process equipment will be defunct. If the generators were preserved then they might be recoverable. Bear in mind that the "design wave" for the lighter structures is a "100-year Wave", so there is actually a pretty good chance that this platform will have seen one of those, plus maybe 10 hurricanes for the North Sea (I think the UK has one per 10 years?) so all the lighter upperworks, such as the accommodation, will have fallen apart.


RP1

 

[CJGibson]

Well, I've experienced three "lumps" that might have been 100 year waves in 27 years offshore, but never heard of one actually reaching the main deck on a platform in the Central or Northern North Sea.

I was on a semi-sub west of Shetland when a lump hit us, green water over deck, and took out the satellite dome. Other semis have had lifeboats torn off in the past.

As RP1 says, unless the plant is kept maintained, it deteriorates rapidly, especially in the splash zone.

The attached was in the Ekofisk field two years ago.

Chris