How to solve "Convergence" and "negetive concentration" error in 1D problem

Usability
1

Dear all,

I am trying to simulate the precipitaiton-dissolution problem and in that case I tried to the follow the CO2 injection benchmark.
Instead of CO2 I tried to inject CaS and also changed other elements but each time I am getting Convergence or negetive concentration error. I tried every possible way I found here to fix the problem but failed.
I am attaching the elements list I used and error message. Please suggest me some way out of the problem. Thank you.
Elements

Error_message
Error_message1121×549 146 KB

2

Hi mmhassan,

did you check if you get any negative concentrations if you switch off the reaction entirely?

You seem to have advection in the system. That can lead to oscillations in the FEM solution even without chemical reactions.
You probably should fix these oscillations first before adding chemical reactions to you model.
One option for that is numerical stabilization. You can check the following and the linked prj files therein:

The error occurs in process no. 11. This is S(+6), I think. Do you have special BCs for that species? E.g., a concentration jump at the boundary?

I hope that helps.

Best regards,
Christoph

3

CPS_All_elements.zip (37.1 KB)

concenptual setup
concenptual setup1184×418 13 KB

Dear Sir,
Firstly, thank you so much for your respond.
I just tried without reaction and it worked without any error. So, the problem is in chemical system I guess. My plan was to follow the calcite precipitation-dissolution benchmark and the conceptual idea I have attached.
Beside, I attached the .prj file I prepared for the work. Please have a look. I will be looking forward to learn from you.
Thank you again.

Sincerely,
Md Mahmudul Hassan

4

Hi,

sorry for the late response.

You wrote that without reaction OGS can solve the problem.

But do you get negative concentrations anywhere in your solution without concentration? If that’s the case, I guess there will always be the error message from OGS. Unfortunately my knowledge of Phreeqc and how to use it with OGS is very limited and I cannot really help, sorry.

Generic advice would be: if you get negative concentrations without reaction, try to overcome them first. One possibility might be to gradually ramp up the Dirichlet BC for S(+6).

Best regards,
Christoph

5

Hello Sir,

Thank you so much for your reply.

I will keep trying and looking here if someone can share any idea to solve negetive concentration problem in OGS for reactive transport model.

Sincerely,
Md Mahmudul Hassan