Problem on decreasing CO2 fugacity, porosity and increasing pH in a reaction using REACT

[thais98]

Hello,

So, I'm trying to follow the steps from a paper, in order to understand the process they made in the software. Firstly, they injected CO2 fugacity in a water sample and the result is an increase in the CO2 fugacity to 68.88 and an increase in the porosity. On the second step, they stop injecting CO2.From what I understood, the resulted solution of the reaction with CO2 is reacted with the minerals that constitute the rock. Their results showed a big decrease in the CO2 fugacity (from 68.88 to 3), porosity and an increase in the pH.

However, when I tried to replicate this second step, I didn't get this result at all. My results indicate only a slight decrease in the CO2 fugacity (from ~68 to 63 ). In relation to the pH, something strange happens, which I couldn't figure out why. There's a increase peak, but not considerable in the pH, then it decreases a little bit and then increases again, but actually it increases nothing, only 0.2. And regarding the porosity, it happens quite the same thing as the pH. 

I'm not sure what I'm doing wrong, I think maybe there's something to do with the reactants that I added. 

I'm attaching the file of the reaction of the step 2 I made. 

Thank you !

fase 1 react luben CO2 mais agua 2.rea

[Jia Wang]

Hello Thais98,

I am not sure what the authors of the original paper did but here are a couple suggestions for you to start troubleshooting. 

It seems like all you have prescribed kinetic rate laws for all your minerals. If you expect similar results, it's important to check that the parameters that you are using (log Ks, rate constants, etc) are the same as the original authors. Also, are they constraining the mineral reaction as a kinetic reaction (as you did) or as equilibrium reactions? If so, you should add your minerals in the Reactants pane as simple minerals instead of kinetic minerals. Another thing to check is that to see if the minerals are dissolving and precipitating similarly to that of the simulation in the paper.

I also noticed is that you specified a porosity of 27.3% in the medium pane but mineral volume only adds up to be about 10% of your system according to your Reactants pane. The remaining undefined volume is automatically assumed to be an inert volume. You can see this if you plot Mineral, Fluid, and Inert volume under Physical parameters. You might want to constrain your minerals as volume percent instead of mmol/kg so that you're putting in accurate mineral percentages. 

Hope this helps,
Jia Wang

[thais98]

Hello, Thanks for the answer!

Regarding the parameters I used are the same same as the author's. They added a table with the kinetic rate parameters of the minerals that I input in the results, so I guess they constrained the mineral reaction as kinetic. The authors don't specify the minerals that dissolve and precipitate. But all of the minerals that I added have a %volume of the compositional mineral assemblage from the aquifer and the rock. 

I did what you suggested, changed the mmol/kg to volume %, but I got the following error:        -- Error: Porosity of node 0 is too small: -0.069483 . I'm not sure what it means.

[Jia Wang]

Hello Thais98,

I tried your original script again but this time I changed all your kinetic minerals to simple reactants and got results much closer to what you expected in your original post. I would recommend double checking against the paper and perhaps emailing the authors to clarify the constraints on their model. 

With regards to the porosity, that suggests that the mineral volume is greater than 100% of your node volume. Perhaps you should check your conversion if you are converting from mmol/kg or the composition in the original paper. 

Best regards,
Jia Wang

[thais98]

Hello, 

I tried to change the kinetic minerals to simple, the CO2 fugacity decreased a lot and the pH increased. However, the porosity didn't decrease, when it should have. Regarding the mineral volume, I changed it to wt% but the output was the same. I will try sending a message to the author.

Thank you for the help!