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Isotope fractionation


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Dear Brian,


I have a question regarding the isotope modeling of GWB.


I have a system that CO2 is being injected into the cell at a constant rate. I am tracking how C isotope of CO2 is changing as it dissolves in brine. There are calcite calcite and dolomite in the system. They have a baseline C isotopes.

I would like to simulate isotope of the CO2 injected during kinetic reactions of calcite and dolomite. Is this possible with GWB? I am getting very high unrealistic values for this simulation.


I did the same thing for equilibrium reactions. The results were good and as we might anticipate.






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Yes, you can account for isotope fractionation along with kinetic reactions. Are you sure that you've chosen appropriate initial values for your fluid, minerals, etc.? Have you segregated/ unsegregated minerals consistently between your two models? Are the non-isotope results comparable?




Brian Farrell

Aqueous Solutions LLC

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Dear Brian,


Thanks for your advice. I will check the carbon isotope values for fluid and carbonate to see if they are appropriate. I pulled those data from different sources.


In both model, i have segregated the minerals. Is that right way to do? Thanks very much.

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Choosing to hold minerals segregated or unsegregated depends on the extent to which your system is in isotopic equilibrium. You can read more about it in Chapter 19 of the Geochemical and Biogeochemical Reaction Modeling text. I think the important thing is that the models that you're comparing are consistent.




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