Overcome Hydrate Formation impact

[Khansahib]

The well fluid at a pressure of 1100 psig and 90 deg F is fed to a scrubber. The gas quantity in the well fluid is 10.5 mmscfd whereas liquid is around 1200 BLPD (oil+water). The part of the gas at 1000 psig is to be used as lift gas whereas around 40% of the gas is to be fed back into production manifold along with the liquid from the scrubber for onward transfer to another platform for proper separation and disposal. The production manifold is being operated at 145 psig. The platform is unmanned and without power. I am sure that there will be hydrate formation in the gas line at the pressure reducing Control Valve as the pressure is reduced from 1100 psig to 145 psig. I also have fear that LCV at scrubber will also choke up due to pressure reduction from 1100 psig to 145 psig. I thought about Methanol injection but in an unmanned facility it is a difficult proposition and would like to avoid. Well fluid does not have enough heat that I can take tubing and wrap around PCV and LCV to keep them warm. I need expert opinion as how to deal with this problem.

 

[GregLamberson]

Khansahib

I see no one has responded, let me jump in and maybe get some discussion started.

Are you sure about the hydrate formations? You do have some high operating pressures and press drops whihc will cause hydrtaes, but your temperature is not too low. Just a question.

Have you looked at heat tracing? Apart from heat, methanol or glycol injection is the only things I know of to prevent hydrates. If you use heat, you will need to get the temp above the hydrate point.

Also be extremely careful if you have a hydrate build up and need to remove it - there could be multiple hydrates.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[Khansahib]

Greg,
Thanks for a cautious jump, if you read 5th line of my thread it says there is no power therefore heating option is out. Regarding hydrate formation, general rule of thumb is for every 100 psi pressure drop the temp drop is 6 deg F. I have mentioned 1000 psig but it may be sometime 1100 psig and so is the temperature which might fluctuate. Keeping all these factors in mind the design has to be fool proof.

 

[GregLamberson]

Khansahib

Sorry, I missed that line. Without power, as you mention heat application (most common) is not possible. What about a small gen set? Apart from heat (tracing, hot water, or steam), then as far as I know, that leaves glycol or methanol.

If glycol is used, it should be sprayed into the stream as small droplets. Without good mixing, there's a chance the glycol injection will not prevent hydrates.

While proper glycol injection can prevent hydrates if injected properly, if you already have them, glycol will not dissolve hydrates as will methanol.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[dcasto]

The gas will hydrate. But you have a good idea. Because you have a large mass of water and oil as compared to the gas you finally mix and send it out with, you can put in a heat exchanger. Take the gas stream going to the header and drop the pressure to 500 psig. The temperature will drop to 61F and the hydrate point is about 51F. Then take the oil/water after the LCV that is about 85 F and warm up the gas from 61F to 75 F. When the gas pressur is dropped from 500 psig to 150 psig, the temperature will be 52 F and the lowest hydrate temp is 32 F.

NOW, I just guessed at compositions and there will be some variance of the above values based on real composition.

 

[GregLamberson]

dcasto

A question, sorry for hijacking, but I thought the hydrate point was around 64 degrees? Don't remember exactly where I got that, but if you don't mind, where did the 51 degrees come from?

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[Khansahib]

dcasto/Greg,
Good proposition I had almost the same type of solution in mind that drop the pressure of the gas to 500 psig and also release the liquid from the separaor at 500 psig and comingle them at this pressure. Istall another Pressure reducing valve down the line to drop down the pressure equivalent to manifold pressure.

Thanks for the input.

 

[dcasto]

GregL, I ran Peng-Robinson on a made up gas analysis. As I stated, you could have a gas with lots of combinations. The old McKetta chart shows 52-53 at 1000 psig.

 

[AndreChE]

Inject methanol. Hydrates will disappear.