Half a croissant, on a plate, with a sign in front of it saying '50c'
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ACR - Deepwater oil spill mitigation

Anchored Collector/Riser for Gulf oil spill
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Three hefty anchors (e.g. concrete blocks) placed around and nearby a leaking subsea well. Cables from each anchor extend in and up to a cone-shaped collector funnel. Going up the funnel it transitions into straight tube and all the way up to tensioning mechanism on an offshore rig e.g. a MODU.

The three cables that hold the collector, they go through pulleys or hefty eyelets at the anchors. The other ends of the three cables go up to the platform and are used to steer the collector. E.g. operate all three together to raise/lower, or individually or in tandem to move the collector side-to-side.

The whole riser string should have a working pull strength of a few tons at least for safety, but the collector and/or riser tubing could be made of a non rigid material. Layflat hose springs to mind... diameter like 18 inches. That way if any crystals of gas hydrates build up, they can be shrugged out.

At the riser head, gas and oil go into a separator tank. Gas to the flare stack, crude into a tanker.

So to summarize my plan:

Step 1: Bring in MODU or drillship with riser tensioning gear

Step 2: Lower three anchors to the seafloor, nearby around leak, each about 20 feet from the leak or as circumstances dictate. Drop and place anchors individually, using doubled cable.

Step 3: Attach three cables to collector/riser. Attach other three to take-up spools.

Step 4: Drop collector/riser. Simultaneously take up other cable ends.

Step 5: Establish tension and position collector.

Step 6: Install separator tank and plumbing.

Step 7: Allow well to produce through the riser until it is depleted or capped.

afinehowdoyoudo, Jun 16 2010

A sketch of the idea http://howdymam.dev...m/art/ACR-167952641
[afinehowdoyoudo, Jun 17 2010]


       I should mention that a tensioned marine riser is an existing part of offshore drilling operations. It is used as a temporary conduit from the rig down to the well. Normally it would be anchored to the wellhead. In this case the bottom-end is modified with an oil collector and anchors.   

       The tension on the riser keeps it from being pushed around and damaged by ocean currents.   

       Riser means a pipe in which material flows upwards.
afinehowdoyoudo, Jun 17 2010

       If the 5000 foot riser was full of oil at a density of 0.8, it would be about 500 psi lighter than the same height of seawater.. so the separator tank would be at 500 psi if the riser was full, or proportionately less if the riser held water part-way up.
afinehowdoyoudo, Jun 17 2010

       This is very similar to the LMRP (Lower Marine Riser Package) aka 'top hat' that is in place now. Which in turn is similar to the larger containment dome that failed after being plugged with gas hydrates. It's not clear to me why oil is still spewing out if the LMRP is in place...   

       Some differences (aside from the obvious divide between reality and a HB idea!) are that this would use: a tensioned riser, cables on the anchors to position the collector, no attempt to seal the collector to the wellhead/xmas tree, a large diameter & non-rigid riser tube.   

       Gas hydrates blocking the riser tube would be a problem. Remotely-operated vehicles (ROV's) would have to 'massage' the riser tube from the outside to break them loose, or a robot 'pig' could be sent down (and back up) the riser to keep it clear.   

       Although a non-rigid riser tube would help prevent the accretion of hydrates, it could collapse under the side-pressure of ocean currents.
afinehowdoyoudo, Jun 17 2010

       It seems that in all these ideas clathrates are effective obstructions. The russians realised this a few decades ago.   

       Let's examine why almost no amount of "cap-n-tap" will work. Any laminar flow that is restricted will speed up as it flows through the "bottle neck" (google venturi effect). That creates a lower pressure. Low temp, low pressure = big freeze. And funny enough that freeze will stick. Almost as if the flow knows there is a bottleneck up front.   

       So fucking cap the flow with fucking gas hydrates, as the universe (or at least this planet )has done, for the last x billion years. Use the force...Luke.
4whom, Jun 17 2010

       Hydrates (clathrates, and other names) require water to form. So, unless there is water in the oil deposit, no crystals will form in the well borehole. It is the mixture of petroleum and seawater at the leak that is causing hydrate crystals.   

       Hydrates can be dealt with: when I worked as a gas tester there was one gas well that formed a hydrate plug in the flare line almost every night (just in time so that we had to deal with it before day shift arrived). We would cycle the valve between the separator tank and the flare line to create a pressure spike that would blow the plug out. Likewise, with a suitable riser design I think any amount of hydrate crystals can be handled. Hence the idea of a non-rigid riser tube... although that has problems too...
afinehowdoyoudo, Jun 17 2010

       There is certainly enough water down there. If you shape your pipe well enough you couldn't blow that plug out (down there at a increasing pressure rate approx 1 atm per 10 m of water ambient) without creating a serious seismic event.
4whom, Jun 17 2010

       I'll give you a bun if you rename this Conical Clathrate Buttplug, which, IMHO, is the only way to solve this mess. Cleaning up the mess that has been already made is another story.   

       The only other way is a nice big vortex. Or several smaller ones. They have the advantage of being positive feedback loops. They also happen to be another way the universe solves these sorts of problems.
4whom, Jun 17 2010

       possible solution leaked
beanangel, Jul 21 2010


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