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Jared Smith

Effective or Total Porosity in TOUGH2 EOS1

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Jared,

 

I believe that you would want to use effective porosity, but am really not sure about this one.  I would recommend that you submit this on the TOUGH forum hosted by LBL.  The TOUGH authors are definitely the most qualified people to answer this question.

 

Thanks,
Alison

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TOUGH2 (Pruess et al., 1999) does not distinguish between 'total' and 'effective' porosity. A look to the way the mass balance equations are written shows that 'total' porosity is used.

I was working with an in-house version of TOUGH2 to simulate the waterflooding (with a polymer) in oil reservoirs, and we had the need to account for a fraction of the pore volume which is not directy displaced by the injected fluid. Actually, we wanted to simulate that a fraction of the water saturation (the connate water saturation) was not displaced by the polymer solution.

We tested two different approaches:

 

1. use a dead pore volume approach, following what is done in ECLIPSE by Schlumberger.  The accumulation term for the polymer was modified as shown below.

 

image.png.b1d4aedb4d58fbe02e3d79cffc490b37.png, where Sdpv is the dead pore volume water saturation.

 

2. use a MINC approach with 2 nested media. The internal one was emulating the fraction of pore volume not directly accessible to the injected fluid,  actually that containing the connate water. The other was representing the effective porosity. The approach was inspired to the work by Falta (2000) Numerical modeling of kinetic interphase mass transfer during air sparging. Water Resources Research, 36, 12, p. 3391-3400.

 

By a proper choice of model parameters, the two approaches were equivalent as far as the transport of polymer is concerned.

Of course the MINC approach makes directly inaccessible the 'connate' water to all the mass components simulated.

 

The first approach requires the modification of source code. The second one can be used with the standard TOUGH2 version, but requires the doubling of the element number.

 

Alfredo

 

 

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