How to simulate mixed gas injection with Toughreact v1.2

Hi

I am trying to develop a model that is used to simulate a mixed gas to inject into a formation, and then get a gas-water- rock reaction model.

The mixed gas includes CO2 and H2S and H2.

which eos should I use? eos 3?  I am not sure.

Now, I am using eos3, and I add an extra cell where the air mass fraction equals 1.

In the extra cell, a gas zone including CO2, H2S, and H2 is set.

However, I can not get a low pH in the cell that connects with the extra cell.

I have no idea what the problem.

According to the conceptual model, the cell connected with the extra cell should have a low pH because the extra cell is a large volume of mixed acid gas.

So, do you have any suggestions?

Thank you so much.