Dual porosity within a column filled with sandstone particle

[Caroline]

Dear sir,

I just wanted to be sure of my calculation about porosity in mobile cells and porosity in immobile cells during transportation.

I want to model a flow within a column filled with sandstone particle, and this sandstone has a porosity of 10%. I want to consider this porosity within the particle as my "immobile volume".
The sandstone particles occupy 50% of the total column volume. I attached a simplified scheme of my problem.

According to the name of the parameters, I was tempted to say that porosity in the mobile cell is 100% and porosity in the immobile cell was 10%. But in the user help, it is written '[...] expressed as fraction of the total volume of mobile AND immobile cells'.
Then, is it right to say that my porosity in the mobile cell is 50% and that the porosity in the immobile cell is 0.5% ?

Thanks a lot for your help

Caroline