# Discussion Forum

## Dubinin Sorption Model on Dual Porosity System

 Topics: 3.5a, Porous Media, Fluid Flow
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Andres Bracho

January 29, 2013 10:09am UTC

Dubinin Sorption Model on Dual Porosity System

Hope this message finds you all well. I have a little technical question. I am currently trying to build a dual porosity model using the earth science module of comsol multiphysics 3.5a. However, I have hit a little bit of a roadblock and I do not know whom else to ask. As well as dual porosity I am trying to model coalbed methane sorption by using the dubinin sorption model. Using this model the matrix storage term turns out to be

Matrix Storage=c1*exp(-(c2*ln(c3/p))^2)

where c1, c2, and c3 are constants and p is the pressure in the system. and the second term of the material balance equation turns out to be the derivative of this matrix storage. The problem is that comsol's default equation has the second term of the material balance equation expressed as da*p' where da is the damping mass coefficient and p' is the derivative of pressure with time. However, using the dubinin sorption model it is not possible to simplify the equation in such a way that it ends up with a coefficient multiplied by a time derivative of pressure. I have tried fiddling around with the equation system but it has yielded no results.

Any ideas on how to modify the equation system so as to fit my dubinin model? Any help on the matter will be very gratefully appreciated. Attached is a word document with the numerical model, perhaps it makes the question clearer. Appologies if the question is not very clear, or if it is very long winded, it is my first time in this forum.

Kind Regards,

Andres Bracho.

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