Mass boundary conditions at an injecting well

Hi,

Can anyone help?  I'm trying to simulate the injection of a known volume of water, with a known concentration of salinity (40 000 mg/l)  into the model.  I can therefore calculate the mass flux in g/d.  This suggests I should be able to use a 4th kind mass boundary condition, as the units of g/d agree with the units used here (mg/l x m^3/d).  I tried combining a 4th kind mass and a 4th kind flow boundary, so I had specified mass injected and volume injected, but the results of the budget analyser did not agree with the mass I was trying to inject.

The other suggestion I've had is to use a 4th kind flow boundary to inject the water and combine it with a 1st kind mass boundary (for concentration).  The problem here is that there is also significant lateral flow in the slice.  The budget analyser shows a mass flux in from both a 1st and a 4th kind boundary, but only the 1st kind boundaries were for mass, the 4th kind were for flow, so I don't really understand the output, or how to properly ensure that only the realistic mass flux can enter the model at the location of the injection well....? ! ?  ??? ???
Any help would be greatly appreciated as I'm getting pretty confused about how to do this!

Cheers very much,

Gemma

Hi Gemma,

The issue you have is related to the way how the mass flux BC are defined and about the choice between the two formulations of the transport equation (divergence form, convective form).

Please have a look at the attached document, it should explain the theory behind it.

If you have problems with the lateral flow, using a finer mesh should increase the accuracy of your model (Because less water is flowing laterally through your cells, where the 1st kind BC is prescribed).

best regards,
Alex.

Alex,

thanks very much for your help,

Gemma