A coutnerintuitive idea to plug the gusher

May 31, 2010 2:30 AM

Please tell me why this idea about stopping the unstoppable gusher will not work: I remember vaguely learning of something called Venturi's law in science class - that if you restrict the flow of a fluid, the pressure goes up. Thus to lower the oil pressure enough to allow the mud to push it down, perhaps they should actually open it up rather than try to plug it.

It seems that the top kill has been failing because they cannot counteract the pressure of the oil enough by injecting dense fluids to push the oil down into the hole: the mud and junk just gets blown right out before it can even accumulate above the oil to push it down. It seems the logical thing would be to open up the well, not try to squeeze it tighter: doing so would lower pressure (as well as release a disturbing volume of oil) but if the pressure can be lowered enough by de-constricting the well, say, by opening the bop rather than trying to plug it up, it could lower the upward pressure enough that a very quick, powerful injection would kill it more easily. If it were possible to lower the wellhead pressure enough to pump mud at a higher pressure, it seems like a win. Perhaps they could cut off the bop, and stick a humungous hose in there, and just pump at a higher pressure to accomplish the top kill. What is wrong with this idea?

posted by Astragalus to technology (10 answers total)

Well, I don't know anything about fluid dynamics, but I imagine the idea of opening up the well so that it releases even more oil won't go down too happily!
posted by katrielalex at 2:43 AM on May 31, 2010

Well, they are trying to drill relief wells to reduce the pressure, but say it will take months to complete.

I assume that drilling the current hole larger would be no easier/quicker than drilling a second nearby hole.

As to why it takes a few months to drill a well, I'm not sure - but they are working with drills a mile long, so I guess it's not as simple as the sort of drilling DIYers are familiar with.
posted by Mike1024 at 2:46 AM on May 31, 2010 [1 favorite]

A really Q&D answer:

(1) Venturi deals with compressible fluids, among other things - different situation. Water/oil would be considered incompressible. (restriction ... I think you mean that the pressure goes down, velocity goes up ...)

(2) The hole is relatively narrow now, so friction is probably playing a significant role in slowing down the flow. If you widen the hole, you decrease the effect of frictional losses, so mass flow would increase. And it would increase simply from having a larger cross sectional area.

I would think of this as a hole-in-the-bucket situation.
posted by coffeefilter at 2:55 AM on May 31, 2010

On second thought, disregard (1), above, it's partially inaccurate. Here's a new improved Q&D answer that better addresses the concepts:

It's important to distinguish between force and pressure. Pressure is not force. Pressure doesn't push things around. Force does.

Force = Pressure * Area. You have pressure X at the hole. If you increase the area of the hole, you increase the force pushing out a hypothetical stationary plug. Pressure at the hole is defined by the surrounding conditions (e.g., overlying rock squishing it, the earth heating it).
posted by coffeefilter at 3:40 AM on May 31, 2010

As to why it takes a few months to drill a well, I'm not sure

The New Orleans newspaper had an excellent article yesterday that went into the reasons this is so incredibly difficult, takes some time, and may even fail the first time. I liked that they explained everything in terms that anyone could understand.

If I'm understanding the poster's question correctly (not about horizontal drilling, but about making the existing well larger), I don't know if it helps explain arguments against that proposal, but maybe it does because it just provides a bigger understanding of what's going on down there.

If you think your idea has merit, or might be useful even in part, you can and should send it along to BP and the Coast Guard. They've received over 7800 ideas already, and they evaluate every idea submitted. The Deepwater Horizon Response website has a page with the idea submission telephone number and a link to a .pdf form for online submission. After reviewing your idea, they will let you know the outcome -- this is probably only a short response (they are pretty busy, and the ideas are really piling in), but at least you get some feedback.
posted by Houstonian at 3:57 AM on May 31, 2010 [5 favorites]

The venturi effect involves pressure and the size of the opening based on a given volume of fluid. A hole that is 200 feet wider will reduce the amount of pressure at the hole, but the same volume of crude will still be escaping.
posted by yclipse at 4:02 AM on May 31, 2010

A relief well, despite the name, doesn't relieve pressure. It just adds a working location (with a working blowout preventer and associated connections) for you to force kill-weight mud into the wellbore.
posted by ctmf at 7:34 AM on May 31, 2010

That is, the only way to stop this thing is going to be to get a static head of heavy mud on top of the resevoir at the bottom, so that resevoir pressure can't force the mud back out. Widening the top of the hole might let you get mud down to where it narrows again, but then you're back to the same problem there. You'd pretty much have to ream out the entire hole way far down until the vertical column of mud was heavy enough to overbalance the resevoir pressure.

May as well just drill the relief well, have a working BOP on it, and not have to drill against outward flow/turbulence (drill string vibration damage)/reduced visibility, etc.
posted by ctmf at 7:40 AM on May 31, 2010

I appreciate the creative thinking here. I just wanted to clarify the Venturi Effect. When a flow of fluid (compressible or not) is restricted to a smaller pipe, the pressure goes DOWN. The velocity, of course, goes up. See Wikipedia.

So if you widened the top of the leaking well the pressure of the oil/gas mixture would increase. The velocity would decrease. I don't know about the volume of oil. I suspect it's being restricted by the blowout preventer somewhat. So if you removed the blowout preventer to drill, you would increase the flow. But after that, widening the top of the hole probably wouldn't do much to the overall flow since you've got a huge long hole below that that is offering resistance to the flow. That is, a well that's through 10,000 feet of rock will leak the same as a well that's through 9,900 feet of rock plus 100 feet of widened well.
posted by huckit at 1:02 PM on June 21, 2010

Thanks everyone for the informative answers - I guess it's sorta moot now - they put on the cap and stopped the flow to test if there are leaks elsewhere. Not sure why they didn't either a) do this way earlier or b) not bother and drill the friggin relief well already. But what do I know. Handy to have to the cap of course because they still get to drink the proverbial milkshake (although they burn at least some of it, maybe for show - I'm a cynic). Let's hope the relief well really does put an end to this. Interestingly I read somewhere the Macondo well has humongous amount of oil in it, enough to gush without slowing down for at least a decade. I but BP is gonna be bummed they have to kill it... Anyway if you can, live in city and take public transit, or ride your bike! Maybe in a few zillion years they'll be burning us instead of the prehistoric microorganisms that make up oil now...
posted by Astragalus at 5:36 PM on August 1, 2010