Mass balance of ECO2N
I was simulating constant CO2 injection into a 2D aquifer (salt not considered). For such 2-phase 2-component system, there should be 2 mass balance equations for CO2 and H2O, respectively, as the following figure shows:
When I calculated the above equations manually based on the output file of TOUGH3-ECO2N, I found that
equation (2) is almost near zero, with maximum residuals around 1E-6. However, the residuals of equation (1) is far from zeros (around 0.001). Note that the dimension of the above equations is [kg/m3/s], so the injection rate of CO2 was divided by the volume of the well element.
My questions is why the residuals of mass balance of component CO2 is larger than H2O? Was the above equations exactly the same as TOUGH3 solves?
3 replies
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Inside the TOUGH3, the convergence criteria for mass and energy balance equations are relative mass error (mass changed/total mass). or absolute mass error. Whenever one of them is reached, it is considered converged. You are using the absolute error.
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Thanks for your reply, Kenny. However, I see from TOUGH3 mannual that the absolute error criterion is set as relative error (=1E-5) timing absolute error (=1). In such way, is the absolute error still 1E-5?
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Yes, the criteria for convergence of mass error applied in your case is also 1.0e-5. But if the total mass >1,0e-5, the relative mass error criteria will be used.
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