The relationship between capillary pressure and saturation is one of the most basic and important issues of multiphase flow in porous media. The-state-of-the-art of theoretical models on capillary pressure-saturation relation as well as the progress of Leverett-J function are reviewed and discussed

and then the capillary pressure-saturation equations for liquid-gas two-phase fluid in a single spherical cavity are derived through geometry manipulation. Calculations are performed for solid-liquid contact angles of 10°

30°

60° and 90° using such equations

the obtained results are consistent with the experimental data in the literature

providing a rational explanation for the variation characteristics of the capillary pressure-saturation curve.