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# Confusion about CTOT and CGUESS

Hello,

I am quite confused about how to provide initial chemistry to TOUGHREACT.

If I want to tell TOUGHREACT that my pH is 6 and calcium concentration is 2mol/kg H2O, how should I proceed?

The manual mentions that if ICON = 1, then theoretically, CTOT for pH should be approximately 10^(-6) and CTOT for Ca2+ should be approximately 2. However, when I look at sample problem #6, 2D CO2 sequestration problem, I see that the CGUESS values make a lot more sense than CTOT values. CTOT for H+ gives me a pH ~ 1.3 and I simply do not think that is correct.

I definitely realize that I am not completely understanding the setup TOUGHREACT is using and I appreciate any help in this matter.

Kind regards,

Majid

## 9replies

• TOUGHREACT Developer
• Eric_Sonnenthal
• 9 mths ago
• Reported - view

Hi Majid,

Every concentration can be entered in different units depending on the ICON value. It is described in the manual. If ICON = 0, then it is pH or ppm for other species. ICON = 1, then it is molality (for 1 kg H2O), ....

cheers,

Eric

• Majid_Trf
• 9 mths ago
• Reported - view

I think I did not read the manual properly. CTOT is the total concentration of the species and CGUESS is the concentration of the individual species.

Hence why CTOT is always larger than CGUESS. Am I correct here?

regards,

Majid

• seashell_airplane
• 9 mths ago
• Reported - view

Can you please explain the values input in CTOT and CGUESS, with reference to sample problem 6, except for H2O?

• Majid_Trf
• 9 mths ago
• Reported - view

Sure.

I cannot go over all of them because you will get the idea once I go over one or two.

First of all, open the TOUGHREACT_V4-OMP_UserGuide_090721 file. Go to page 62/158.

ca+2     1    0.4479E-02    0.4737E-02    *       0.0

Under composition of aqueous solution:

NAPRI = Ca+2

ICON = 1 -> your CTOT value will be the TOTAL concentration of calcium. [Ca+2]=0.4737E-2 (mol Ca+2)/(kg H2O)

CGUESS = 0.4479E-2 -> if you know the chemistry of your brine, you have to make a decent guess for TR to calculate how much total calcium you have in your system coming from your primary and secondary species. You are making a guess as to how much individual primary species you have here.

CTOT = explained above.

NAMEQ = 0 -> ICON is not equal to 2.

QKSAT = 0 -> ICON is not equal to 2.

--------------------------------------------------------------

What I have done in my own simulations is that I know what the individual concentrations of my primary species are, inputted those in CGUESS, and when I run a chemical initialization simulation, TR calculates how much CTOT I have in my system for each species.

If you know salinity, pH and the temperature in your system and what kind of species you have present, you can calculate the individual primary species concentration using an excel sheet and some of the info provided in chdump.

Hope this helps.

Majid

• seashell_airplane
• 8 mths ago
• Reported - view

Thank you for this explanation.

I have another question, it is regarding INCON and inchem file. How can I update these files to include parameters from the flow.inp file, such as porosity and permeability? Additionally, when I read the INCON file, I understand that the first line of every element is showing the porosity and permeability , but I am unclear about the second line. Could you please explain the parameters defined in the INCON and inchem files?

• Majid_Trf
• 8 mths ago
• Reported - view

INCON already includes porosity and permeability values for every block in your mesh. Your SAVE file is also your INCON when you use the RESTART function. In order to update inchem, you would have to write your own code to do that for you.

The second line of INCON is:

Pressure (pascal), salinity (%), mass fraction of CO2 or gas phase saturation (depending on the fluid phases present), and finally temperature (C).

Refer to page 11 (or page 7) in "TOUGH2-ECO2N_V2.0_Users_Guide" pdf.

• seashell_airplane
• 8 mths ago
• Reported - view

If I make changes to my 'flow.inp' file, specifically adjusting the porosity and permeability, how can I ensure that these modifications are reflected in the 'INCON' file? I've noticed that when I execute the 'flow.inp' file with new values, the resulting 'SAVE' file still contains the old porosity and permeability values. The same is observed in the new 'savechem' file.

• Majid_Trf
• 8 mths ago
• Reported - view

Create a new directory, run your new simulations there with the new porosity and permeability values. you do not need to necessarily include an INCON file for your simulations to run. You can create a blank INCON section in your flow.inp file.

I am not sure if I completely understand your problem but whenever you run a simulation, you should be able to see the effects in the SAVE file.

• seashell_airplane
• 8 mths ago
• Reported - view

Thank you so much. I am able to see the effects in the SAVE file now.

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