Characterization of Capillary Pressure-Saturation Relationships for Double-Porosity Medium Using Light Transmission Visualization Technique

Capillary pressure saturation (P-c-S-w) relationship plays a central role in the description of fluid flow in porous media. In this research, the light transmission visualization (LTV) technique was applied to characterize the P-c-S-w relationship in a double-porosity medium. Four experiments were conducted in two-dimensional (2-D) flow chambers packed with a double-porosity medium composed of a mixture of silica sand and sintered kaolin clay spheres. In each experiment, a different volumetric fraction of macropores and micropores was used. The experiment was also repeated by compacting the flow chamber with silica sand only to represent single-porosity medium. Variable saturations of water across the height of the system were applied by controlling the capillary pressure. Images of the 2-D model were collected using a digital camera and analyzed pixel by pixel to determine water saturation in the double-porosity medium. Results from the LTV technique showed that the P-c-S-w relationships for all experiments in double-porosity soil medium were similar in shape but varied depending on the porous media composition. Comparison with the pressure cell test results showed that the P-c-S-w curves for all experiments consistent comparable to those obtained by the LTV technique. The P-c-S-w curves were also fit to van Genuchten model for comparison and validation. For double-porosity media, the best-fit parameters were consistent with published data for sandy clay. Moreover, little variability was observed in the best-fit alpha and n values for the different double porosity. Overall, this study proves that the LTV technique is a noninvasive laboratory tool that can provide high-resolution spatial data for water saturation distribution in different types of porous media and is capable of producing highly resolved P-c-S-w relationships.