The Impact of Sample Size on X-Ray Microtomography Measurements of Fluid–Fluid Interfacial Areas

This work investigates the impact of sample size on the measurement of non-wetting/wetting interfacial areas in porous media by X-ray microtomography (XMT). Standard-sized small columns and significantly larger columns, both packed with sand, were imaged using the same industrial XMT system (IMT). Additional small columns were imaged using synchrotron XMT (SMT) to evaluate the comparability between the different systems. The mean bulk densities and porosities for all three imaged sets are statistically identical, indicating that column preparations were robust. The mean non-wetting/wetting interfacial areas measured for the large columns for the low and moderate NAPL saturations (Sn), were 11.3 cm−1 (Sn = 0.13) and 15.3 cm−1 (Sn = 0.22), respectively. The mean interfacial areas measured at the moderate Sn for the two small columns imaged by IMT (16.7 cm−1, Sn = 0.24) and imaged by SMT (16.9 cm−1, Sn = 0.21) are consistent with those of the larger column. In addition, the mean interfacial area measured at the lower Sn for the two small columns imaged by SMT (9.4 cm−1, Sn = 0.12) is consistent with that of the larger column. The results indicate that the small imaged volumes typically used for XMT are sufficient to establish REV conditions for measurement of fluid–fluid interfacial areas in this sand.