Quantitative Analysis of Flow Processes in a Sand Using Synchrotron‐Based X‐ray Microtomography

Pore‐scale multiphase flow experiments were developed to nondestructively visualize water flow in a sample of porous material using X‐ray microtomography. The samples were exposed to similar boundary conditions as in a previous investigation, which examined the effect of initial flow rate on observed dynamic effects in the measured capillary pressure–saturation curves; a significantly higher residual saturation and higher capillary pressures were found when the sample was drained fast using a high air‐phase pressure. Prior work applying the X‐ray microtomography technique to pore‐scale multiphase flow problems has been of a mostly qualitative nature and no experiments have been presented in the existing literature where a truly quantitative approach to investigating the multiphase flow process has been taken, including a thorough image‐processing scheme. The tomographic images presented here show, both by qualitative comparison and quantitative analysis in the form of a nearest neighbor analysis, that the dynamic effects seen in previous experiments are likely due to the fast and preferential drainage of large pores in the sample. Once a continuous drained path has been established through the sample, further drainage of the remaining pores, which have been disconnected from the main flowing water continuum, is prevented.