Quantification of Fluid Saturations in Transparent Porous Media

Abstract

Core Ideas Imaging techniques are powerful for investigating multiphase flow in porous media. Transparent porous media can be used to quantify local fluid saturations. Efficient methods to calibrate intensity–saturation relationships are required. Our new procedure uses fewer images and measurements. Predicted saturations based on calibrated images matched independent measurements. Experiments using transparent porous media, where the indices of refraction of the solid grains and the wetting fluid are matched, can be used to quantify fluid saturations from digital images. In this study, significantly more efficient calibration and validation methods for unsaturated transparent porous media were developed, which used just three images and one saturation measurement. Imbibition and drainage column experiments were used to define the pixel intensity and saturation at residual wetting fluid saturation, as well as at residual nonwetting fluid saturation in two gradations of transparent porous media used for validation. The other images were pixel intensity at 100 and 0% wetting fluid saturation. Results from the drainage and imbibition experiments on the two transparent porous media gradations showed a log‐linear saturation–pixel intensity relationship, which agreed with the validation points from this study as well as those using a previous calibration method. We expect that this new calibration procedure will allow efficient development of saturation–pixel intensity relationships for the investigation of multiphase flow using transparent porous media under a variety of conditions.

An Improved Method for Quantifying Liquid Saturation Using Transparent Soil

“…e calibration relationship between the saturation S w and normalized intensity I N can be obtained using the above procedure, and the results are shown in Figure 5. In the figure, the black squares represent our experimental data, while the white circles represent the data obtained in previous studies of Peters et al [23] and Sills et al [25]. e red solid line represents the fitting curve of all the data in Figure 5.…”

“…It was first defined by Selker et al [38]. e similar equation (5) has been used in other studies in transparent porous media and light transmission [5,23,25,37,39]. In this study, it is important to note that the pixel intensity is darkest when it is utterly saturated due to the black background behind the column, while the opposite is true for light transmission.…”

“…Transparent soil appears white when it is completely dry, and it is transparent when fully saturated. Between these states, some researchers have worked on the correlation between the pixel intensity and saturation of partially saturated transparent soil [23][24][25][26].…”

“…Accordingly, a two-dimensional moisture profile of different drainage stages of the soil column was obtained. e transparent soil used in this study is a fused quartz sand [23,25,31], comprised of uniformed fine sand with a particle size ranging from 0.5 mm to 1.0 mm and a refractive index of 1.459. e particle size distribution curve obtained by laser particle size analyzer (Malven, MS-2000) is shown in Figure 2. Relevant soil properties are summarized in Table 1.…”

Thirty-Ninth Canadian Geotechnical Colloquium: Unsaturated soil mechanics — bridging the gap between research and practice

“…At 297 90%, discrete air bubbles are visible while at lower saturations the soil visually lightens continually until 298 its dry. Details on the digital image process can be found in Peters et al (2011) and Sills et al (2016). 299…”