Hydrates

[AreJay]

Hi all,

Looking at the gas lift on a process and wondering about hydrates.

The gas goes through dehydration before final compression where it is moved down to lift other wells.

By the time the gas gets to the wells it has cooled down to around 7/8oC which bring the gas into its hydrate zone. The platform currently inject methanol into the lift gas in fear of hydrates but this is the 1st time I have ever seen this.

Surely with all gas lifted wells by the time the gas gets subsea it must have cooled to within its hydrate zone? Do most platforms have methanol in the lift gas?

Thanks in advance

 

[zdas04]

Flow assurance is a hot topic on platforms right now. Unfortunately many companies spell "flow assurance" m-e-t-h-o-n-o-l. If it is present at the point where hydrates want to form, it will delay formation. The problem is that it is nearly impossible to have coverage everywhere, and transporting methonol with gas is an iffy proposition. I see methonol as a grossly overused hazardous chemical that is almost never properly applied.

David

 

[dcasto]

go to this site for all of your needs.

http://hydrates.mines.edu/CHR/Pub-Theses.html

Think about the gas lift gas as it returns the fluids from the well, those fluids are loaded with water. The methanol is not to keep the lift gas going into the well from freezing, its the gas and fluids coming out that will have the highest peobability of hydrate formation

 

[AreJay]

The producing wells are flowing at 40bar ish with a temperature of 40/50oC... it is the point where the gas lift is at the injection valve into the producing fluid where the gas is at its lowest temperature and will surely be at more risk of hydrate formation?

What I cant understand is how all platforms dont need to inject methanol because the gas lift before entering the production fluids will be at high pressure and low temperature... unless all the water has been removed in dehydration then surely everyone will be at risk?

 

[PaoloPemi]

in Europe hydrate inhibitors are about the same products used as water antifreeze inhibitors : methanol, ethanol, glycols, calcium chloride... according my tables at 8 Celsius you should expect hydrate formation in a range 10 Bar (gas sg about 1) to 70 Bar (CH4), however accurate calc.s can give very different values which depend from adopted model, in fact for a specified composition I wasn't able to obtain the same values from different software tools which is possibly the reason why inhibitors are so frequently used.

 

[AreJay]

Yeah I ran the hydrate curver and it shows that the composition is in the hydrate region... mainly due to the temperature... the wells are so far away that the gas is so cold coming over the valves.

I thought the whole point of a dehydration system would be to eliminate the risk of hydrate formation, however dehydration and inhibition is now used.