Hi,
I have a situation where a porous medium is initially saturated with gas (e.g. methane not air) at 300 psi. The geometry is a square. From the top boundary water has to enter the medium and compress the gas. The water/gas saturations, pressures, will change with time. There is thus the role of capillary pressure which is taken care by van Genutchen correlation. The relative permeability relationships are derived from Brooks & Corey. Both capillary pressure and rel perm are functions of saturation. I am using two darcy law modules for this. I am following the COMSOL's 'Two phase column' project.
The problem is when initial gas pressure inside porous medium is 300 psi, and the top boundary water pressure is 500 psi, COMSOL runs into an error and Pc = Pg - Pw becomes negative. If Pw < Pg then there is no water diffusion into the matrix. Can somebody please help me out.
Thanks