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# Constant gas production rate

We are using EWASG modulus to simulate a reservoir with water, salt, and NCG.

For the production well, there are water and NCG production. We know that we can set  total (gas + liquid) production rate in GENER file. But, we want to set constant NCG(gas) production rate for the source/sink cells. Is there any way to set constant NCG production rate?

Thanks

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• Dear Ozawa,

requiring a constant NCG production rate when a multicomponent mixture is present might not be physical.

But going to your question from a purely modeling point of view:

1. do you want to simulate the production of a mixture with a constant NCG rate fraction, or

2. do yo wany simply to extract only a fixed NCG rate?

I think TOUGH2 cannot support option 1 above, while option 2 can be implemented by assigning in GENER the NCG rate using COM3=NCG rate (negative for extraction).

This GENER option was coded for injection purposes and the user has to supply the rate and enthapy of each injected mass component, but the code can use also a negative rate value to simulate the extraction of a given component. Apart for the physical meaning of this approach, there is a couple of additional issues:

- continous extraction of one component at a fixed rate may deplete the mass of that component below zero in the element from which the extraction is simulated, as there is no limiting constraint.

- you need also to assign the enthalpy of the extracted component, as the code is not instructed to compute that enthalpy. And computing a meaningful enthalpy for the NCG component (which may also vary as thermodynamic conditions changes) is not straightforword.

I have never used this approach for the NCG, but once I used it to simulate the evaporation of water from a lagoon in order to model the progressive increment of salt content in the lagoon which was connected to the sea. I assigned the evaluated evaporation rate using COM1 (for the water component). In that case I assigned the extraction enthalpy equal to the enthalpy of aqueous phase, without major errors. if I remember well, I had also to specify a value different than 0 to ITAB.

Hoping it may help.

Regards,

Alfredo

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