Gas relative permeability: equation ???
Hello everybody,
I have one question regard the document Tough v2, in "tough v2.0 manual" , we assume krg=1-krl if Sgr=0, we found that this is very strong assumption and which is not confirmed by the experiments. Beside i found that 2 equations of gas relative permeability: one in "tough v2.0 manual"(page:185) and one in "TOUGH2TrainingMaterial", they are not consistent. Could you explain the exact equation of gas relative permeability which is used in TOUGH.
Thank you in advance
Quan
2 replies
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Dear Quan,
The equation currently implemented in TOUGH2 V2.1 is the one from the TOUGH manual, not that from the short course material. (The slide you cite is from the general tutorial on multi-phase flow, i.e., it does not refer to and does not claim to be a specific function implemented in TOUGH2).
I agree with you that the assumptions underlying the equation krg=1-krl are very specific. That is the reason why an alternative model (that of Corey, 1954) is provided. You can engage the Corey model by setting RP(4)>0 (if you want residual gas saturation to be essentially zero, set Sgr to a very small but non-zero value, e.g., RP(4)=1E-6).
In general, relative permeability and capillary pressure functions need to be customized frequently; they are essentially the responsibility of the user; hence the note at the end of Appendix G, p. 187.
The equation from the TOUGH Short Course material is that of Luckner et al. (1989). Note that the famous van Genuchten (1980) model does not include a function for krg, as it was developed for unsaturated flow in soils. The Luckner model is implemented in iTOUGH2.
Hope this clarifies things.
Stefan
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Dear Stefan,
Your explain is clear and useful for my problem. I think that I could solve it now. Thanks so much!