The difference between phase pressures due to difference in fluids interaction with rock martix:
| (1) | p_{cog} = p_o - p_g |
| (2) | p_{cow} = p_o - p_w |
One of the string assumptions in fluid dynamic modelling is that capillary pressure is a function of saturation only:
| (3) | p_{cog} = p_{cog}(s_o) |
| (4) | p_{cow} = p_{cow}(s_w) |