Physical correlation for capillary pressure on reservoir saturation:
P_{cow} (s_w) = \frac{ (\sigma \cos \theta) _{ow} } { \sqrt \frac{k}{\phi}} \; J_{cow}(s_w) |
P_{cog} (s_g) = \frac{ (\sigma \cos \theta)_{og} } { \sqrt \frac{k}{\phi}} \; J_{cog}(s_g) |
where
| oil-water surface tension | oil-gas surface tension | ||
| oil-gas contact angle | oil-gas contact angle | ||
| absolute permeability to air | porosity | ||
| some function of water saturation | some function of gas saturation |
The functions and
are called Leverett J-functions.
They are individual to every certain rock type, just like relative permeability curves.
There are many correlations for Leverett J-functions and the most popular is Brooks-Corey correlation: