PhreeqcUsers Discussion Forum

Processes => Reactive transport modelling => Topic started by: zsszabo86 on May 14, 2019, 03:09:34 PM

Title: transport - mixture 1
Post by: zsszabo86 on May 14, 2019, 03:09:34 PM
Hello

I have run into two problem which I did not see before. I run reactive transport simulations and want to model a scenario when CO2 containing water flows into a geological formation. I have problems with both ways I figured out:

1. I start the code like this:

SOLUTION 0
temperature   135
pressure   272.8
units   mol/kgw
pH   5.029
pe   5.059
Al   1.92E-06
C(4)   4.99E-01
Ca   2.03E-03
Cl   4.93E-01
Fe   4.26E-06
K   4.05E-02
Mg   2.16E-03
Na   4.63E-01
S   5.13E-02
Si   5.45E-03

GAS_PHASE 1   
   -fixed_pressure
   -pressure 272.8
   -volume 5000   
   -temperature 135
    CO2(g) 272.8
   
SAVE solution   0

END

USE solution 0

etc.

then it seems that the gas phase can be completely used up and then there is no more CO2 coming into my cells with solution 0 (even though I believed that the saved solution 0 is CO2-saturated). other words: it seems that not the new saved solution 0 is used and it also seems that the gas phase is used not only for calculating the solution 0 composition but it is in all cells

it would be great to get some explanation of what is happening

2. The other way was to simulate the CO2-containing solution in a different model then to copy paste the result as the solution 0. it seems ok to do that but then no reaction happens. and looking at the output I see that the solution 0 is not flowing into cell1. see below 0.000e+00 Solution 0 and also see in attachment.

Mixture 1.   

     0.000e+00 Solution 0   Solution after simulation 2.                           
     6.677e-01 Solution 1   Solution after simulation 2.                           
     3.323e-01 Solution 2   Solution after simulation 2.       

Again, I cannot figure out why the solution 0 is not flowing in and advice would be helpful.

Thank you in advance!                   
Title: Re: transport - mixture 1
Post by: dlparkhurst on May 14, 2019, 09:50:58 PM
Assuming you are using TRANSPORT, solution 0 has the additional CO2 needed to produce a partial pressure of 272.8, and it will be advected into the column with each shift, provided you have specified a flux boundary condition at cell 1.

If you specify diffusion only, solution 0 will not be advected into the column.

Not sure about a constant boundary condition, but I think cell 1 would be maintained at the solution 1 composition, and solution 0 would not affect the calculation.

Alternatively, you can specify GAS_PHASE 1, which would continue to react with cell 1 throughout the calculation, although the CO2(g) pressure will continuously decrease. You may want to specify CO2(g) in EQUILIBRIUM_PHASES 1, which would maintain the CO2(g) partial pressure throughout the simulation (provided you give a large amount of moles in the definition).
Title: Re: transport - mixture 1
Post by: zsszabo86 on May 15, 2019, 09:34:44 PM
Many thanks for the useful reply! It finally opened my eye, what the problem is (it is diffusion only!!!) and how to solve it.