An improved method for the determination of capillary pressure-saturation curves involving TCE, water and air

Most capillary pressure ( P c )-saturation ( S) curves are determined with a pressure or tension apparatus containing a porous medium sample of often >5 cm in height. If the porous medium sample consists of a coarse-grained material and the interfacial tension between the wetting and non-wetting fluid is sufficiently low, it is not inconceivable that large changes in S occur over the height of the sample. Using the standard procedure of measuring the outflow volume of one of the fluids, from which average values of S are then calculated, can therefore result in substantial errors. In this study a method is proposed to measure P c − S drainage and imbition relationships for TCE-air and TCE-water systems at points along a 1-m-long column with the help of a γ-radiation system and from knowledge of the fluid pressure distributions at hydraulic equilibrium. The results show that S-values changed from complete saturation to their residual values, and vice versa, over P c changed ranging from 2.5 to 10 cm of water pressure, which makes the use of, e.g., a pressure cell a dubious procedure for certain fluid systems.