Is Methane Supercritical at 3500 psig and 176 deg F?

[davisb]

I'm doing some research/lab analysis on methane. Is methane considered a supercritical fluid/gas at 3500 psig and 176 deg F?

Critical point is about -116 deg F and 673 psia.

 

[JLSeagull]

Is it rational to believe that a 10% temperature increase could raise the critical pressure from 673 to 3515 psia?

Search for a methane phase diagram, likely at NIST.

 

[EmmanuelTop]

I think we are mixing apples and oranges here? Methane is a pure substance with critical temperature 190.4K and critical pressure 45.4atm. Knowing this fact, at any pressure and temperature above the critical values, fluid is in the supercritical region:

http://en.wikipedia.org/wiki/Supercritical_fluid

Please correct me if I missed something.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[dcasto]

Emm, you are correct

 

[maddocks]

How do you describe the zone where the fluid is above critical pressure but below crit temperature? ie., is it a subcooled critical fluid?

 

[dcasto]

I'd call it a liquid, but who cares. There is nothing special going on.

 

[maddocks]

Actually we often find ourselves in this zone of interest in acid gas applications, CO2 sequestration, CO2 miscible flood regions....the accurate prediction of physical properties in this area is important.....and it's always good to be able to explain to people what the fluid is doing...

 

[dcasto]

I've done AGI and my 3 different silulations were within a a couple of hundred psi from matching actual. What we can't model well is the formation drop.

Another thing is dynamic simulation of the injection. The methane can stratify or not "disolve" exactly like simulations, so the injection wells will "gas" up.

 

[maddocks]

Actually my theory is that the wellbore acts like a multi-stage distillation column that allows the higher volatility methane and nitrogen components to migrate to the top of the wellbore and depress the fluid level forcing the injection pressure to rise to overcome the loss of injection head.....

 

[dcasto]

well, the present equalibrium data doesn't allow for that. But I believe that we look at equalibrium to much. There are random "bell curves" of methane "solubility" in liquid CO2 and once in a while a molecule will not be in equalbrium.

This "non equalibrium" gas will rise in the casing. But then what happens is the density of the injection fluids drop and therfore the head on the liquids and then even less methane stays in the liquid and the surface pressure must be increased to get the bottom hole pressure high enough to overcome its native pressure plus pressure drop into the formation.

Now I could imagine a distillation type system at low injection rates. The head gain by the 60+ lb/cf fluids would overcome the energy needed to vaporize the methane and the column would be flooded and no separation.

It would be a fun simulation and something to look at in the lab. But the solution is always, get the methane out and be prepared to degas the well every so often, even if we did know and or agree on the mass transfer situation. Distill or non equalibrium based on "drunkards walk" theory of random mechanics.