Dewatering gas lift pipe line

[tbvn]

Hi all,

I am looking for a procedure of dewatering gas lift pipe line.Can some one help me on this issue.

Best regards
tbvn

 

[zdas04]

I hate to always be the jerk here, but your question is pretty wide open. Are you talking about (1) removing hydrotest water once; or (2) removing condensation on an ongoing basis? How much water are you talking about? How long is the line? How big is the line? What is the normal operting pressure and normal injection volume? What part of the world are you in (is the water in the line subject to freezing)? Is the gas-lift gas dehydrated?



David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"It is always a poor idea to ask your Bridge Club for medical advice or a collection of geek engineers for legal advice"

 

[BigInch]

... or lawyers.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[tbvn]

Sorry all for this question.

I am a brand new in this area and I am trying to learn from you all as much as possible.

Actualy we are preparing dewatering gas lift pipe line from Subsea tie in point to our facility.After we have complted hydrotest this pipe line, there is apr 360m3 water left inside.The hole lenght of this pipe is 7 km and ID is 10 inch.we have installed a bi-dir pig and pressure upstream of pig is 100bar.

I am looking for a procedure of dewatering gas lift pipe line for prepare our procedure.

Hope this clear and you can help me.

BR,

tbvn

 

[BigInch]

see this thread,

http://www.eng-tips.com/viewthread.cfm?qid=258654

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

The thread that BigInch pointed you to is trying to get a line absolutely dry. That is occasionally required, but not often. For a gas lift line, you are injecting the gas into a well that has oil, gas, and water in it so adding a bunch of humidity isn't often a problem.

So to "dewater" your line I would:
1. Determine a legal way to dispose of the water removed. This can be a bigger problem than anything else since the nice clean water you used to fill the line is now "waste" and many countries will no longer let you dump it on the ground. I've had to haul my test water to disposal wells (your project is around 2,200 bbl so this is not a small thing).
2. Then I would run a couple of foam pigs towards whichever end the disposal method is on. There will be some bypassed water with two pig runs, but your line will either use dehydrated gas (which will evaporate the left-behind water within a few days or weeks) or you will need to regularly pig the line and the left-behind water will get pigged out with that.

You dry a line down to less that 50% relative humidity when it has something that liquid water can hurt, I don't think that is the case for a gas-lift line.

David

 

[BigInch]

zdas, good point.

He can stop the procedure whenever he thinks its dry enough to run (mostly) gas and probably do it again the next month or so.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[tbvn]

Thanks all for your advise.

I got solution now.

BR,

tbvn

 

[NMcC]

You dry a line down to less that 50% relative humidity when it has something that liquid water can hurt, I don't think that is the case for a gas-lift line.

My apologies, I feel this assumption is incorrect and need to point out the following:

High concentrations of methane, ethane, propane (i.e. lean export/lift gas) and the very likely presence of free water even after dewatering (10" ID is not a small line, in fact HUGE for gas lift) combined with low ambient temperatures (Subsea line) and high (enough) pressures @ approx 100 barg represent perfect hydrate formation conditions. Even if the lift gas is dehydrated, the free water in the line will be ready & waiting for it.

The dewatering procedure needs to address this issue. In fact, in most cases, this is mitigated against by the use of a suitable mix of MEG/Water as the initial hydrotest fluid.

I hope we are not too late in pointing this out...

The only saving grace is that, if the 10" ID is correct, it will take HUGE amounts of hydrates to block it completely...


Nick McCarthy
Flow Assurance Consultant

http://www.linkedin.com/in/flowassurance

 

[zdas04]

I guess if you are a "flow assurance" guy then every problem looks like a flow assurance problem. The OP was talking about removing hydrotest water, not the water that may accompany injection gas. The flow assurance or hydrate risk associated with hydrotest water is approximately zero and the advice above will get the total mass of water low enough that hydrates are not a concern with regard to the hydrotest water.

For ongoing injection, the OP needs to look at the mix of gases (I rarely see anything heavier than methane in gas lift gas because the other stuff is too valuable as NGL and is less effective in gas lift) and the amount of water vapor in that gas (again, it is pretty common to use dehydrated gas for gas lift from shore for the issues you raised).

David

 

[Alph]

I agree with NMcC's comments above.

Bulk de-watering off subsea gas lift lines is not sufficient ensure that hydrates don't form.

Generally due to terrain, sufficient water can collects at low points leading to hydrates in the line or downstream of gas lift chokes on the tree.

Generally you would use a train of b-dir, foam or gel pigs with MEG/water [80/20] between the pigs. The driving force provided by Nitrogen or product gas.

In UK, BG guidelines are used to calculate MEG quantities required in the pig train. I will have a look if I can get extract from these guideline.

Regards
Al

 

[Alph]

Glycol Swabbing

See attachment for claculating glycol volumes.

Regards
Alph