3-D Microscopic Measurement and Analysis of Chemical Flow and Transport in Porous Media

Chemical flow and transport have been studied at the pore-scale in an experimental porous medium. Measurements have been taken using a novel nonintrusive fluorescence imaging technique. The experimental setup consists of a cylindrical column carved out of a clear plastic block, packed with clear beads of the same material. A refractive index-matched fluid was pumped under laminar, slow-flow conditions through the column. The fluid was seeded with tracer particles or a solute organic dye for flow and chemical transport measurements, respectively. The system is automated to image through the porous medium for collecting microscopic values of velocity, concentration, and pore geometry at high-accuracy and high-resolution. Various geometric, flow, and transport quantities have been obtained in a full three-dimensional volume within the porous medium. These include microscopic (pore-scale) medium geometry, velocity and concentration fields, dispersive solute fluxes, and reasonable estimates of a representative elementary volume (REV) for the porous medium. The results indicate that the range of allowable REV sizes, as measured from averaged velocity, concentration, and pore volume data, varies among the different quantities, however, a common overlapping range, valid for all quantities, can be determined. For our system, this common REV has been estimated to be about two orders of magnitude larger than the medium’s particle volume. Furthermore, correlation results show an increase in correlation of mean-removed velocity and concentration values near the concentration front in our experiments. These results have been confirmed via 3-D plots of concentration, velocity, pore geometry, and microscopic flux distributions in these regions.