Visualization and quantification of transport processes in porous media using micromodels.

摘要

Micro-scale visualization can provide valuable information to enhance the understanding of pore-scale transport phenomena. In this research, various transport processes were physically simulated in micromodels and quantified by employing image-analyzing techniques. Micromodels are artificial models of porous media that can be used to simulate transport processes at the pore-scale.; First, solute transport was experimentally simulated and numerically quantified in a homogeneous micromodel. Experimental observations were compared with the numerical results of an advective-dispersive solute transport model which treated the micromodel as a macro-scale porous medium, and also by using a two-dimensional discrete fracture model in which the network of channels was treated as a set of mutually orthogonal fractures.; Next, dissolution of residual nonaqueous phase liquids (NAPLs) was directly observed in a heterogeneous micromodel and was quantified by processing video images with an image analyzer. Temporal changes in residual NAPL volumes were measured and mass transfer rates of trichloroethylene (TCE) were evaluated. Relationships among mass transfer rate coefficient, mass transfer coefficient, residual saturation and flow velocity were examined. A methodology for evaluating separate coefficients for dissolution in the mobile and immobile water region was introduced by measuring the fraction of total residual NAPL in contact with mobile water, immobile water and solid glass surfaces.; Finally, surfactant enhanced dissolution of toluene and TCE by four commercial surfactants was studied. The effects of such variables as flow rate, surfactant concentration, and porous medium properties on dissolution were investigated.