Improved Computational Procedure for Retention Relations of Immiscible Fluids Using Pressure Cells

The capillary pressure-saturation relation, or the capillary pressure head-volumetric fluid content relation, is of widespread interest in modeling and predicting multiphase fluid flow. A common procedure to determine this relation is to use a pressure cell and assume uniform distributions of capillary pressure and volumetric fluid contents at static equilibrium. The pressure cell method, however, yields inaccurate results for certain combinations of multiphase fluids and porous media. The sensitivity analysis in this study shows that the pressure cell height, the positions of the pressure measuring devices, which can coincide with the in- and outflow ports, and the relative density difference of the fluids, can give rise to considerable errors in the determination of capillary pressure head-volumetric fluid content relations by the standard procedure using pressure cells. We, therefore, propose a curve-fitting method that considers nonuniform distributions of capillary pressure and volumetric fluid content of multiphase fluids. The method uses the same input data as commonly used procedures.