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chance

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Posts posted by chance

    Isotope fractionation

    in The Geochemist's Workbench

    Posted

    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.

     

     

    Thanks.

     

    Regards.

    GWB handles coal?

    in The Geochemist's Workbench

    Posted

    Hi Chance,

     

    GWB can certainly model sorption, but you'll need to search the literature so that you can create a surface dataset for coal. You should follow the format of the FeOH.dat surface dataset installed with the GWB. Basically, graphite would be your sorbing mineral, and you would add a surface basis species which is an uncomplexed site. You would then add a surface species for the CO2 surface complex. IF you don't want to use a full double layer model, you might also find a Langmuir model to be sufficient.

     

    You might want to set up some sort of kinetic rate law to describe the formation of CH4.

     

    Regards,

    Brian

     

     

    Thank you a lot, Brian.

     

    I will look into the sorption part of the GWB.

     

    Thanks again.

     

    Regards.

    GWB handles coal?

    in The Geochemist's Workbench

    Posted

    Hi chance,

     

    It sounds like you can use React's isotope fractionation model, described in Chapter 19 of the Geochemical and Biogeochemical Reaction Modeling text. Graphite should suffice as a proxy for coal in your model. The mineral is included in the default thermo dataset thermo.dat as well as the compilation of fractionation factors isotope.dat.

     

    Regards,

    Brian

     

     

    Dear Brian,

     

    Thanks a lot for your kind help. Yes, Iam using that isotope model. Did not know how to include the coal in the model. I will use graphite as a mienral then.

    One more quick question again, does GWB do adsorption of CO2 on coal (or graphite)and production of CH4. Thank you.

     

    With regards,

    Chance

    GWB handles coal?

    in The Geochemist's Workbench

    Posted

    Hi Chance,

     

    Can you be a little more specific? Coal is more of a rock than a mineral, so the nature of your problem will dictate how to set up your model.

     

    If you're interested in the generation of acid mine drainage, for example, you can certainly model the oxidation of the sulfide minerals present in coal.

     

    Hope this helps,

     

    Brian Farrell

    Aqueous Solutions LLC

     

     

    Thanks Brian for such a quick reply.

    Im looking at the isotope farctination between injected CO2 and DIC in a formation water. However, the formation has coal layers. I was trying to include coal into the model to see any its impact on the isotopes. But no idea how to do so.

     

    Thanks a lot.

    Cation exchange reaction

    in The Geochemist's Workbench

    Posted

    Thank you Brian. You helped a lot. Now its working. I didnt know that at first, I would open the surface dataset in addition to the thermo dataset.

     

     

    Regards,

    Chance

     

     

     

     

     

     

     

    Hi Chance,

     

    The thermo datasets and surface datasets are used differently by the GWB programs. A thermo dataset is always necessary, but a surface dataset is not (only when you want to model surface reactions). You should not replace the thermo dataset with the surface dataset - you simply open a surface dataset in addition to the thermo dataset. This should be done at the beginning of the run, not the end.

     

    As for what goes into the surface dataset, I can't help you with your selectivity coefficients. You do need to change the format of your surface dataset, however. I would recommend following convention and using a monovalent ion as the basis species, so >X:H in your case. The surface species, then, would be something like >X2:Ca (no charge on surface species), made up of the species -2H+, 2>X:H, and Ca++. Where you define the surface species, you need to specify the correct number of species needed to form it (3) and make sure that the coefficients are correct to make a balanced reaction (>X2:Ca + 2H+ = Ca++ + 2>X:H).

     

    Hope this helps,

    Brian

    Cation exchange reaction

    in The Geochemist's Workbench

    Posted

    Hi Brian,

     

    I have a question for you again.

    I am trying to model the Ca++ exchange reaction on illite surface with H+ ion that is produced from CO2 dissolution in the brine.

    I prepared the cation exchange dataset for this reaction according to the example file IonEx that came with the software as you suggested.

    First I am using thermo dataset for the CO2 dissolution in the brine under 50 atm. Then,after I got the pH decreased, I changed the dataset to IonEX to model the illite surface exhange reaction between Ca++ and H+.

    But I think I am doing something wrong.I dont know the selectivity constant for this echange reaction. So, I am also playing with this parameter.

    Can you look at my files?

    Thank you.

    IonExIllite.datillite_exp.rea

    Hi Brain,

     

    Thank you for your reply. You helped a lot.

     

     

    Regards,

     

    Chans

    Error

    in The Geochemist's Workbench

    Posted

    Thank you Brian. You helped a lot!!

    We didnt see any siderite dissolution in our lab work although we were expecting some dissolution. And then we tried to model our experiment. The model observation was same too. But i was not sure if i was conceptualizing the problem correctly with the sliding fugacity option of the program. Now I see it is the appropriate one after i discussed it with you. Now the fugacity of a gas is very clear to me. Thank you again for your kind help.

     

     

     

    Regards,

    Chans.

    Error

    in The Geochemist's Workbench

    Posted

    Hi Brian,

     

    Thank you for looking at my file. The pH=8.5 is the pH of initial brine. As the CO2(g) dissolves in the initial brine, I see that, in the model, the pH value is dropping to around 5 and more CO2 (aq) are being produced. So defining the CO2 fugacity as sliding at 50 atm is right?

     

    In our work, no siderite dissolution was observed. The model results shows no siderite dissolution either. Do you think our numerical model does not really reflect the conceptual model correctly?

     

    Also one more question to make sure one thing?? I thought fugacity was something related to the CO2 gas not to the CO2 (aq) species? Do you mean that as CO2 gas dissolves in the water, the CO2 fugacity increases?

     

    Many thanks!!!! You have been so helpful!!!

     

    Regards,

     

    Chans

    Error

    in The Geochemist's Workbench

    Posted

    Thank you Brian,

     

    I did get the run. But this time I want the CO2 fugacity at 50 atm. But i dont know how to define it in the model. There are 2 options as far as i understood: 1. fixed fugacity (I guess it is fixed at only atmospheric CO2. 2. Sliding fugacity.

     

    I dont want varying fugacity. How can I define set the CO2 fugacity at 50 atm.

    I am attaching the react file.

     

    Thanks again.

    Regards,

     

    Chans

    siderite(kinetics)_exp1.rea

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