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tracer diffusion in CO2

Hi

I am modelling Helium diffusing from formation water into injected CO2 (with the ECO2N module in toughreact v3). However I am unsure about how the diffusion coefficient for He in CO2 is set in the model? Is it defined by DIFUNG? Can the model actually account for He diffusion within the CO2?   

thanks for your help and best wishes

carmen

1 reply

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    • TOUGHREACT Developer
    • Eric_Sonnenthal
    • 7 yrs ago
    • Reported - view

    Hi Carmen,

    Yes TOUGHREACT v3 can model He diffusion in the CO2 phase. Two methods can be used:

    1) Set DIFUNG to the value for He in CO2 at 25C. If TEXP in flow.inp is to 0. then only pressure-dependence is used. If TEXP is set to a non-zero value, then there will be temperature-dependent diffusion as well. The formulation here is (where ptg is the pressure in Pa):

    dcfgas= difung*(1.01325d5/ptg)*(tkk/273.15d0)**texp

    2) To obtain pressure-temperature-dependent diffusion coefficients: First set DIFUNG to a negative value (any value like -1.). Then in the thermodynamic database use the He molecular diameter that gives the correct value for He in CO2, or CO2-H2O gas, using the formulation described in the User's Manual.

    regards,

    Eric

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