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 rather 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 imbibition-relationships for TCE-air and TCE-water systems at points along a 1-m-long column with the help of a gamma-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) changes 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.