The results of Example 2 in the ECO2M manual
Hello.
I have a question about Example 2 of ECO2M.
In Example 2 the residual water saturation is set to 0.3.
However, in the results, the water saturation is 0 near the injection well.
Why is the saturation rate smaller than the residual water saturation?
I thought that the water saturation rate could not be smaller than 0.3.
I would be grateful if you could tell me.
2 replies
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Dear Kohei,
a residual water saturation of 0.3 means the aqueous phase cannot be displaced by the injected CO2 below that saturation value, as AQ phase relative permeability is 0. at SAQ less or equal to 0.3.
But the AQ phase can evaporate into the injected CO2. Figure 16 shows that pure CO2 is injected. This means CO2 is undersaturated with respect to water at reservoir conditions. Thus, water is evaporated (TOUGH2 assumes instantaneous thermodynamic equilibrium) into the injected CO2. As CO2 keeps flowing, the water is completely evaporated in the near well zone with a dry-out front traveling from the injection well into the reservoir. Water evaporation concentrates the NaCl which eventually precipitate.
Look at the results of ECO2M simulation. Have also a look to the same problem No. 2 simulated using ECO2N (Pruess, 2005) whose results are fully described in chapter 5.2 of the user's guide.
Regards,
Alfredo