Three-dimensional velocity measurement of complex interstitial flows through water-saturated porous media by the tagging method in the MRI technique

Local velocity measurements of interstitial flow through porous media and observation of the local pore geometry, which strongly influences the flow field, are necessary in order to understand the transport mechanism in a porous system. In order to investigate the effect of pore geometry on the flow field in porous media, three-dimensional velocity measurements of interstitial flow through two porous samples with different pore geometries have been experimentally performed using magnetic resonance imaging (MRI). The porous samples were made from cylindrical tubes in one case packed with crushed glass particles and in the other spherical beads. Based on the observed images of the porous samples, the porosity and pore size distributions as pore structure parameters were determined by image analysis. The two- and three-dimensional velocity vectors of the steady-state flow in the void spaces of the crushed glass sample have been measured using a spin-echo sequence with tagging pulses. The obtained velocity maps show a strong non-uniform flow. In places, reversed flow is induced by the pore geometry. The effect of the mean flow velocity on the change in the flow pattern has been investigated in the mean flow velocity range from 3.84 to 13.2 mm s^-1. The frequency distribution of the axial velocity component of the interstitial flows through the packed beads was broader than that of the crushed glass pack.