Help deciding EOS7C or EOS7CA


I am a researcher looking to model gas (CH4) accumulation beneath a capillary barrier in the shallow subsurface. Currently I have EOS7C available for use but I am considering purchasing TOUGH3 for use of the EOS7CA.

Doing some research on the differences between the two EOS's are that EOS7C "methane (CH4) instead of air"  and "it has a solubility model that is accurate for deep (high pressure) systems whereas the solubility model in EOS7CA is limited to shallow (low pressure) systems" Oldenburg EOS7CA User Manual

I also found that I cannot use Petrasim to visualize the output file when using EOS7CA due to it being a part of TOUGH3. 

Is there any benefit in me purchasing TOUGH3/EOS7CA as opposed to keeping TOUGH2/EOS7C?

Will the output files show that much difference when comparing both codes? 

Should I just purchase the TOUGH3 code and try to visualize the output file through Petrasim?  


Thank you!

5 replies

    • Reservoir Engineer
    • Alfredo_b
    • 3 mths ago
    • Reported - view


    Have you considered to use TMVOC under Petrasim?

    It can handle mixtures of CH4 and air with a thermodynamic description suitable for low pressure conditions.


      • Jordon_Massey
      • 3 mths ago
      • Reported - view


      Unfortunately, I do not have access to the TMVOC EOS in petrasim. This would have been a good option. I am working on my dissertation proposal and have designed it based on using EOS7C. 

      Being unfamiliar with the subtle differences of the codes I am wondering if using EOC7C would still be able to accurately model the solubility of methane under near surface P and T. 

      Also, the modeling of methane in EOS7C as opposed to air statement in the EOS7CA has confused me.

      I assume EOS7C doesn't model air, but is it possible for me to use the near surface concentrations of CO2 and NO2 to simulate air?

      Forgive me if these questions make no sense, just trying to explore the FREE options first.


      • Reservoir Engineer
      • Alfredo_b
      • 3 mths ago
      • Reported - view


      I think EOS7C should give rather accurate thermodynamic equilibria and thermophysical properties of gas and aqueous phases at near surface conditions too.

      EOS7C in TOUGH2/3 models CH4 and one NCG which can be chosen between CO2 and N2. If you need to model the unsaturated zone, using N2 should be a good proxy for air.

      EOS7CA allows you to model air and CH4 mixtures at near surface conditions, as gas solubility is decribed with Henry's law. In principle it should be better for your needs, by using the pseudo-component air instead of N2 such as in EOS7C.

      Probably Curt can give you more detailed suggestions.


    • kenny
    • 3 mths ago
    • Reported - view

    Hi Jordon,

    Most important advantage of TOUGH3/EOC7C over TOUGH2/EOS7C is parallel computing. If you need to run for large models, parallel computing is very important and can get significant speedup for your simulation.

    We are updating TOUGH3 to V1.11. It will be available in the marketplace in a few days.   There is a new module named "EOS7MG" in Ver 1.11. It may work well for your problems.  Key features of the new module include:

    (1) A flexible number of overall mass components (3-5) depending on user needs to lower computation time. The model system can have single-phase (gas or liquid) or two-phase regions, but it must have at least one gas component and at most three gas components (gas components can be fully dissolved in the aqueous phase depending on P-T-X conditions). Computational burden is lower with fewer mass conservation equations (fewer gas components).

    (2) In EOS7MG,  the solubility model remains the same as used in EOS7C which can handle higher pressure. The use of gas-phase mass fraction as a primary variable instead of liquid-phase mass fraction avoids the need for the iterative solution of gas solubility used in EOS7C and improves solubility model convergence behavior significantly.

    (3) A choice of gases relevant to subsurface energy applications: CH4, C2H6, C3H8, H2S, CO2, N2, O2, H2, and AIR.

    (4) Implementation of the viscosity model of Quinones et al. (2000) for accurate viscosities of H2 mixtures. If H2 exists in the simulation, the Quinones et al. method is automatically used as the default.

    (5) EOS7MG allows 4 different types of initial conditions for user convenience.

    (6) As part of TOUGH3, all of the functionality of TOUGH3 is available including parallel computing capabilities.

    • Alison_Alcott
    • 3 mths ago
    • Reported - view

    I just wanted to clarify that PetraSim 2022 and above does support the creation and visualization of TOUGH3 output.  If you are using an older version of PetraSim, this may not be possible  Jordan, I believe that your group has a newer version of PetraSim, but you would really want to contact me directly to confirm this.  PetraSim currently only supports EOS7C.  I think you could adapt the input files created for EOS7C to work with EOS7CA fairly easily.  It may be a little more challenging for EOS7MG because I think there is a different number of primary variables.  I will have to look at this more when TOUGH3 v1.11 is released.

Content aside

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