Mole fraction Output from ECO2N

Hello

 

Trying to get CO2 mass- and mole fraction in aqueous phase and  H2O mass- and mole fraction in gaseous phase from a run with iTough2 and ECO2N in a simple radial 1D model where dry CO2 injected into a saline aquifer with high salinity. Mass fractions seemed to be sensible, but mole fraction of CO2 in liquid doesn’t look like healthy. I wonder, if this is a conversion issue or I may have overlooked something. I used the exact same Tough2 and iTough2 data files. The only exception was formulation of output for the two parameters in question:

 

From:

  >> MASS FRACTION

     >>> ELEMENT        :  ___99

         >>>> annotation: XCO_99

         >>>> COMPONENT     : 3 (CO2)

         >>>> PHASE     : 1 (LIQUID)

         <<<<

     <<<

 

To:

  >> MOLE FRACTION

     >>> ELEMENT        :  ___99

         >>>> annotation: XCO_99

         >>>> COMPONENT     : 3 (CO2)

         >>>> PHASE     : 1 (LIQUID)

         <<<<

     <<<

 

A printout of data for the first 3 grid blocks close to CO2 source is attached, where mole fractions beyond 1.0 are also reported.

 

Will be great if you send me your comments.

Godarzi

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  • Hello Godarzi,

    Can you please attach your input and output files here?

    Thank you

    Yingqi

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  • Thank you for the quick reply.

    Here are the files.

    As you are going to see, it is  a high saline case with a rapid salt precipitation in grid blocks close to the well and this may (potentially?) have something to do with the reported mole fraction_ just a guess!

    The liquid and salt saturation besides the mole and mass fractions are printed for quite a few observation grid blocks.

    Appreciate your feedback.

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  • One additional output:

    Previous output file printed mass fraction. Here is Mole fraction output.

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    • Godarzi K 

      Hello Godarzi,

      I noticed that the .col file you sent has NaNs  ("not a number") for CO2 mole fractions in the gas phase if there is no gas phase present, i.e., for elements under single-phase liquid conditions. The reason for this is that the gas density and gas saturations are zero for these elements, and during the conversion from mass to mole fractions, one has to divide by this molar density. (You can either replace all the NaNs in your file with a zero, or make a one-line code change to avoid the division (in file it2main, subroutine OBSERVAT:

       8889           CONTINUE

                      IF (DEN.GT.0.0D0) XTOUGH=XTOUGH+XMOLP/DEN*VOLX 

       

      Molar fraction may exceed 1 just before the phase change, where the sum of salt saturation and gas saturation approach 1.0, and there is only a tiny amount of liquid in the system. Again, as one has to divide by this tiny saturation during the conversion, round-off error may lead to higher-than-one mole fractions. This round-off error is inconsequential because the tiny amount of CO2 in this tiny amount of water remaining in the pores before it evaporates is insignificant. Alternatively, you can work with mass fractions.

      Thanks

      Yingqi

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  • Thank you Yingqi, for the extended description.

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