use gas lift pump on BP Macondo blowout? 4

[Windward]

To capture the leaking oil and gas until it has been stopped, would a gas lift pump work? There is about 40% methane by mass in the leak. This high percentage of gas would create a very powerful gas lift.

Direct the leak -that is, after the oil/gas has left the wellhead and is in the water at the 5000 foot depth (in other words, I am not suggesting using gas lift in the well itself) - into the open bottom end of a pipe running down to the leak from a salvage vessel.

Once this flow starts moving up the pipe, the highly pressurized methane will continuously expand because the pressure above the mixture is constantly falling. This will reduce the average density of the mixture in the pipe. At steady state flow, it will be much lower than the density of the seawater outside of the pipe.

It would be a giant chimney but with a much greater driving force than if the fluids were gases only, because of the much greater densities and the much greater difference in those densities. If the average density in the pipe is 4/5 that of seawater, the driving force at the bottom of the pipe would be more than 400 psi.

The oil/gas/water mixture will exit the pipe at high velocity at the salvage vessel, perfect for separating the liquid from the gas in a cyclone.

No outside power needed, equipment far simpler and cheaper than what they have been trying.

I know that word - CLATHRATES. They will plug up the flow! But will they, with 400 psi driving it? And if they are a problem, do what they are doing with tophat and put some methanol into it, or some warm water. Not hard when we are looking at the complete destruction of marine life in the Gulf of Mexico and the consequences of that.

 

[Windward]

docellen, you posted a google site here for ideas on controlling the blowout, now the post is gone, wha' happen?

 

[PetroSynergy]

All of us in industry know about relief wells, but here is a crude video from my undergrad alma mater explaining the matter. This will be a good visual reference to those of you who have friends that don't quite understand the process.

http://www.facebook.com/l.php?u=http://

http://www.youtube.com/watch?v=UHnWefOI0aw&h=251ee

 

[Windward]

I haven't made any sketches of the idea, but to size the riser we must know the gas fraction, the total volume flow and the pressure at the blowout. The total volume flow is affected by the gas fraction and the pressure.

At Macondo the pressure is over 2000 psi at the 5000 foot depth. Even though the gas fraction was very high there, over 40% by mass, the volume flow was not large because of the high pressure.

Compare this to Ixtoc, where the water depth at the blowout was 150 feet. Like Macondo, there was a lot of gas, and the total oil flow was about the same. But at Ixtoc, the volume flow was much greater because of the low pressure.

We must also design a collection dome to attach to the bottom of the riser. After the Sombrero was installed at Ixtoc, they found that the dome was much too small. However, that was mainly because PEMEX greatly underestimated the size of the blowout. They said it was 5,000 bpd when it was closer to 40,000.

PEMEX probably knew it was that high, but didn't want to report it even to their gas lift designers, Brown and Root. It appears that BP/USG did the same thing at Macondo. I think they greatly underestimated the flow for public relations. There is evidence that their experts soon knew that the flow was much higher.

At Macondo, they tried the 100 ton containment dome first. This was a gas lift pump like the Sombrero. But they did not account for the formation of gas hydrates, although they must have known this would happen. The hydrates plugged the flow. This problem did not exist at Ixtoc because of the much lower pressure and higher temperature of the water.

Why did BP install the containment dome without any measures to prevent hydrates? And why did they put a 1" orifice in the 6" riser? There are several discussions of this orifice on the Oil Drum. You can find them by searching the site for posts by Jquest and windward. See some of my posts above also.

My answer is that BP wanted to appear to be doing something to get the oil and gas to the surface where it could be collected, but actually wanted to keep as much of it as possible underwater, where it couldn't be seen on the TV news. I also believe that is why they used so much dispersant. We will learn that these tactics caused far greater damage than would have resulted from forcing the oil and gas to the surface for collection or flaring.

Of course, there was no plan or equipment ready for handling the oil and gas at the surface either. But I don't think it would have taken three months to figure out how to do it, if they could have gotten the containment dome to work. They did manage to handle the oil and gas that came up from the last top cap.

It is important to note here a point I have made in previous posts. If a completely effective top cap can be installed quickly, perfectly sealed and no leaks, then there would be no need for a gas lift pump. The gas lift pump is for blowouts that have already entered the water, and there is no other way to quickly capture the oil and gas.

After Ixtoc, the O&G industry should have developed the gas lift pump to perfection, and had some of them ready for deployment. But they didn't want to spend the money, and the US government did not force them to do it because the MMS essentially belonged to the O&G industry. It will be hard to change this even after Macondo. The economy of the GOM and the US depends on oil production. Any obstacles to production such as moratoriums and stricter safety rules will be strongly opposed by many, and many of them will have clout.

However, as Rockman and others have made clear on the Oil Drum, most operators in the GOM and elsewhere would never have taken the risks that BP did at Macondo. It is even less likely now that any operator would do so.

A gas lift pump for extreme depths/pressures, where the temperatures are always near freezing, must be designed to handle gas hydrates. That is mainly what I have been proposing above. We already know that a gas lift pump will work, as long as it is not plugged. We can't reduce the pressure at these deep blowouts, so we must heat the flow in some way to prevent hydrate formation. A poster on the Oil Drum mentioned ultrasound as a possibility. I hadn't thought of that. Maybe microwaves would do it. I don't believe that the injection of inhibitors such as methanol or glycol would be as economic or effective as heating.

 

[Windward]

The equipment appears to be what they finally installed at Macondo. The pdf says:

"...In the event of a future incident, mobilization to the field will start within days and the system will be fully operational within weeks..."

The main apparatus requires the connection of a "subsea containment assembly" to the existing BOP, as at Macondo. If all future blowouts occur at the BOP, and the BOP is still in good enough condition for this connection, so far so good. Until the connection is made and everything is hooked up, the blowout continues, maybe for "weeks".

Suppose the blowout is below the mudline, for example a damaged casing or a bad cement job. Connecting to the BOP won't help. The blowout is already entering the water elsewhere. Apparently the containment plan will be ready for this situation with the "capture caisson assembly". Sounds like an envelope around the leak with a riser to the surface. They intend to seal it to the seabed, to prevent water from entering.

Suppose this device is in place, and the riser is filled with oil and gas. The average density of the column inside the riser will be substantially less than that of the surrounding seawater. The differential pressure will be the greatest at the greatest depth, at the caisson. The seal to the seabed must withstand this differential pressure.

How much could it be? At Macondo, it would have been on the order of 400 psi. The seabed in most places is soft mud and sand for some considerable distance below the mudline. How deep must the caisson be sunk below the mudline to withstand possibly hundreds of psi of differential pressure? I don't know the answer, but I suspect it would be on the order of 100 feet.

I also suspect that it would not be easy to install the caisson because of this sealing requirement, and that it would take considerable time in any case. How large must the diameter of a round caisson be to cover a leak? If the oil and gas are coming up out of the seafloor, the leak cross section could be large.

The containment plan could require the construction of a set of caissons ranging in diameter from ten feet up to, say, 100 feet. They would pick the best size for the leak, but if 100 feet is not large enough, back to the shop for a bigger one. More time lost, and that billion dollars is going fast. In any case, the blowout continues until a big enough caisson is sunk deep enough for a seal, and the riser is connected on both ends.

The sealing problem would not exist with a gas lift pump. For the pump to operate, it requires a path for the seawater outside to flow into the capture vessel, which would be a cone or cylinder. The riser is attached to the top of the vessel. One aspect of the pump design is to keep the water flow to a minimum. The lower the water flow, the greater the driving force of the pump, because the more oil and gas and less water in the column, the lower the density of the column.

The diameter of the capture vessel would not have to be nearly as large as that of a caisson. When the pump is working, it will draw in the leaking oil and gas under it, and if necessary around it also, like a vacuum cleaner. Granted, the wider the cross section of the leak, the more water is entrained in the flow and the less effective the pump. But it still might work well enough on a leak with a cross section much wider than the capture vessel. Time for some studies and experiments. In fact, Jerome Milgram of MIT has already done a lot of work on the idea, but he quit in 1984 when funding stopped. See my 15 June post.

I doubt that it would take weeks to install a gas lift pump over a blowout. It does not require any undersea connections. No messing around with ROVS to remove damaged equipment and install a new stack. No need for all that equipment shown in the pdf. The pump is just a collection vessel and a riser, with a means for heating at the bottom if necessary. The pump would have to be assembled at the site and that would take some time, most likely days not weeks.

caltech69, regarding heating to prevent gas hydrates, I mentioned in an earlier post (30 June) that resistance heaters might work. They could be arranged as a screen with small passageways to minimize the flow of seawater into the system (although if the cross section of the leak is larger than the diameter of the capture vessel, these openings would also reduce the flow of oil and gas that is coming in from outside the vessel - details!). Heat transfer to the water would be very high with such a screen. It would probaly be easier to send electric current down to resistance heaters than it would be to send oxygen down to create a small fire in the flow - if such a fire is possible.

The gas lift pump probably requires at least some gas in the oil. If the leak was nothing but oil, which is also less dense than seawater, it still might work, and it would be an oil lift pump.