TOUGH3-EOS7C failed to converge after 10 years
Hello,
I am simulating an injector and producer doublet in a gas reservoir with TOUGH3-EOS7C. It runs well for the first few years and then struggles to converge with very small time steps (screenshot below).
I looked into the OUTPUT file and did not find any error message. The program struggles to converge mainly on two cells (indicated by the black cross in the screenshot below). But the variables at these two locations look good to me. I do have local refinement as small as 1m by 1m surrounding the wells. My injection rate and production rate are both 30 kg/s.
I plotted the pressure change at both injector and producer
Can anyone please point me what could be the problem or what else I need to check? Thank you for any suggestions.
Regards,
Haiyan
2 replies
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Sorry, the pressure change at the two wells did not show up in the post.
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From the info provided it is not possible to say why the run essentially stops by reducing the time steps until one step does not converge in 9 iterations, while the subsequent one converges at the first one without changing the primary variables.
You should ask for additional diagnostic printout including: info on iterations to know which element and equation has the highest residual; phase change diagnostic to check if phase transitions are related to problematic elements. In this case check RELP and PCAP curves to see if some of their features are related to the encountered issue. Something like appearance/disapperance of gas phase when using van Genuchten PCAP. Check if EOS7C has any issue in solving the thermodynamic equilibrium of NCGs and water/brine mixture.
You should check if at the injection elements one of the mass component is completely depleted; this may happen if you do not inject all the simulated mass components. You should check if primary variables at production and injection elements are always within allowed ranges.
Additional diagnostic printout should tell you where to look further.
Finally, you are using a spatial grid that does not honor the IFD standard method used by TOUGH2/3 to discretize the balance equations. Not sure if this may have a role on the encountered convergence issues.
Regards,
Alfredo