Boundary condition for gas migration

[juntao pan]

Dear all,

I want to simulate the migration of CO₂ in sand strata due to CO₂ being injected into the bottom layer. I hope that the CO₂ will enter the atmosphere from the bottom to the top, so I have set mole fraction conditions. However, no matter what value I set for the mole fraction (0.4, 0.0004 or even 0.000001), the gas saturation does not change. How can I make the goal? I have attatched my codes below.

Since I'm new to PFLOTRAN, I would sincerely appreciate any suggestions on how to set this boundary condition.

Thank you in advance for your support!

Best regards,

Juntao Pan

[Hammond, Glenn E]

Juntao,

 

I added the following block to your input deck to track mass balance at the boundary in the *-mas.dat file:

 

OUTPUT

   …

  MASS_BALANCE_FILE

    PERIODIC TIMESTEP 1

  /

END

 

When I run your input deck using “MOLE_FRACTION 4.d-4” at the top boundary, I get the following output:

 

"Time [y]","dt_flow [y]","Global Water Mass in Liquid Phas [kg]","Global Air Mass in Liquid Phase [kg]","Global Water Mass in Gas Phase [kg]","Global Air Mass in Gas Phase [kg]","open Water Mass [kg]","open Air Mass [kg]","open Water Mass [kg/y]","open Air Mass [kg/y]","gas Water Mass [kg]","gas Air Mass [kg]","gas Water Mass [kg/y]","gas Air Mass [kg/y]"

  3.17097920E-08  3.17097920E-08  2.15400889E+07  5.26461951E-01  0.00000000E+00  0.00000000E+00 -3.21451357E-03  7.71959849E-09 -1.01372900E+05  2.43445258E-01 -0.00000000E+00  3.74775351E-04 -0.00000000E+00  1.18189155E+04

  9.51293760E-08  6.34195840E-08  2.15400889E+07  5.27211545E-01  0.00000000E+00  0.00000000E+00 -7.82623276E-03  2.32031807E-08 -7.27175883E+04  2.44145124E-01 -0.00000000E+00  1.12435364E-03 -0.00000000E+00  1.18193505E+04

  2.21968544E-07  1.26839168E-07  2.15400889E+07  5.28710788E-01  0.00000000E+00  0.00000000E+00 -1.38691262E-02  5.42480254E-08 -4.76421717E+04  2.44757556E-01 -0.00000000E+00  2.62356550E-03 -0.00000000E+00  1.18197863E+04

 

When I run your input deck using “MOLE_FRACTION 1.d-8” at the top boundary, I get the following output:

 

"Time [y]","dt_flow [y]","Global Water Mass in Liquid Phas [kg]","Global Air Mass in Liquid Phase [kg]","Global Water Mass in Gas Phase [kg]","Global Air Mass in Gas Phase [kg]","open Water Mass [kg]","open Air Mass [kg]","open Water Mass [kg/y]","open Air Mass [kg/y]","gas Water Mass [kg]","gas Air Mass [kg]","gas Water Mass [kg/y]","gas Air Mass [kg/y]"

  3.17097920E-08  3.17097920E-08  2.15400889E+07  5.26461943E-01  0.00000000E+00  0.00000000E+00 -1.14653369E-10 -2.80025150E-18 -3.61570865E-03 -8.83087314E-11 -0.00000000E+00  3.74775351E-04 -0.00000000E+00  1.18189155E+04

  9.51293760E-08  6.34195840E-08  2.15400889E+07  5.27211522E-01  0.00000000E+00  0.00000000E+00 -4.95913434E-10 -1.21120064E-17 -6.01170870E-03 -1.46827751E-10 -0.00000000E+00  1.12435364E-03 -0.00000000E+00  1.18193505E+04

  2.21968544E-07  1.26839168E-07  2.15400889E+07  5.28710733E-01  0.00000000E+00  0.00000000E+00 -1.21778619E-08 -2.97427598E-16 -9.21004818E-02 -2.24942812E-09 -0.00000000E+00  2.62356551E-03 -0.00000000E+00  1.18197863E+04

 

It is likely that the large volume of free phase gas that is exiting is dwarfing the diffusive flux.

 

Glenn

 

From: pflotra...@googlegroups.com <pflotra...@googlegroups.com> on behalf of juntao pan <panjun...@gmail.com>
Date: Monday, May 26, 2025 at 4:23 AM
To: pflotran-users <pflotra...@googlegroups.com>
Subject: [pflotran-users: 8405] Boundary condition for gas migration

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[juntao pan]

Dear Glenn,

Thank you for your prompt reply, but I'm don't fully understand you. I think when I change mole fraction in the boundary condition, I changed the fraction of dissolved gas into water. So when either liquid pressure exceeds 101325 or gas mole fraction exceeds 4.d-4, water and gas will migrate out of the domain. Am I right?

Thanks!

Juntao

[Hammond, Glenn E]

Juntao,

 

If you set the mass/mole fraction in the flow condition to be greater than saturation limit for dissolved gas, the code will not form free phase gas at the boundary as for boundary conditions, the code holds the state to be liquid state (since pressure, mass/mole fraction and temperature were defined) and the mass/mole fraction to be what was entered. It will not bubble. If the flow condition is prescribed as an initial condition, the gas phase should form during the first time step.

 

Glenn

 

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[juntao pan]

Hi Glenn,

Thank you very much! Now I have a beeter understanding of this problem.

Juntao