s_w(h)=P_{cow}^{-1}[(\rho_w -\rho_o) g (h-h_{FWL})]

based on implicit solution of the constant pressure gradient equation:

(\rho_w -\rho_o) \cdot g \cdot (h-h_{FWL}) = P_{cow}(s_w)

where  и  – oil and water densities at initial formation temperature and pressure .

This model requires reliable and representative data bank on capillary pressure at sandface conditions.