Correlating Gas Transport Parameters and X-Ray Computed Tomography Measurements in Porous Media

Abstract

Gas transport parameters and X-ray computed tomography (CT) measurements in porous medium under controlled and identical conditions provide a useful methodology for studying the relationships among them, ultimately leading to a better understanding of subsurface gaseous transport and other soil physical processes. The objective of this study was to characterize the relationships between gas transport parameters and soil-pore geometry revealed by X-ray CT. Sands of different shapes with a mean particle diameter (d 50) ranging from 0.19 to 1.51 mm were used as porous media under both air-dried and partially saturated conditions. Gas transport parameters including gas dispersivity (α), diffusivity (D P/D 0), and permeability (k a) were measured using a unified measurement system (UMS). The 3DMA-Rock computational package was used for analysis of three-dimensional CT data. A strong linear relationship was found between α and tortuosity calculated from gas transport parameters ( ), indicating that gas dispersivity has a linear and inverse relationship with gas diffusivity. A linear relationship was also found between k a and d 50/T UMS 2, indicating a strong dependency of k a on mean particle size and direct correlation with gas diffusivity. Tortuosity (T MFX) and equivalent pore diameter (d eq.MFX) analyzed from microfocus X-ray CT increased linearly with increasing d50 for both Granusil and Accusand and further showing no effect of particle shape. The T UMS values showed reasonably good agreement with T MFX values. The k a showed a strong relationship when plotted against d eq.MFX/T MFX 2, indicating its strong dependency on pore size distribution and tortuosity of pore space.