Fundamentals of Fluid Flow in Porous Media

Chapter 3

Diffusion Coefficient: Measurement Techniques

Computer-Assisted Tomography: Effective Diffusion Coefficient

Using CAT scanning give us the opportunity to find effective diffusion coefficient for a porous media. The procedure is the same as the procedure of finding bulk diffusion coefficient except that the vessel is half filled with oil saturated sand and topped with solvent. In contrast to the bulk diffusion coefficient that the region of interest (ROI) was in both solvent and oil region (Figure 3‑24), here ROI includes only the liquid volume in the solvent region because of the complexity of obtaining a smooth concentration profile that could be used in the calculation of diffusion coefficients when including the sand volume (Figure 3‑26). The diffusion calculations were made based on the assumption that the amount of oil that diffused in the solvent is equal to the amount of solvent that diffused in the oil/sand mixture but in opposite direction. The calculation procedure is the same as for bulk diffusion coefficient.

Figure 3-26: Sample of Diffusion in Sand Saturated with Oil

Figure 3‑27 shows the result of CAT scanning experiment for bulk diffusion coefficient of three different solvents in heavy oil. Each point is the average diffusion coefficient over the height of the region of interest (ROI).

Figure 3-27: Average Diffusion Coefficients for Pentane, Hexane and Octane in Heavy Oil