The difference between phase pressures due to difference in fluids interaction with rock martix:
p_{cog} = p_o - p_g |
p_{cow} = p_o - p_w |
One of the strong assumptions in reservoir fluid dynamic modelling is that capillary pressure is a function of one saturation only:
p_{cog} = p_{cog}(s_o) |
p_{cow} = p_{cow}(s_w) |