Preselection of a sorption model based on a column test: the algorithm and an example of its application

In order to describe the contamination of saturated porous media, it is necessary to find an appropriate mathematical model that includes processes occurring in aquifers, such as advection, dispersion, diffusion, and various kinds of sorption. The identification of parameters of those processes is possible through laboratory column experiments, which result in records of breakthrough curves for a conservative tracer and a reactive tracer. An algorithm leading to the preliminary selection of the mathematical model that best describes transport processes of the reactive tracer in the experimental column is proposed in this article. A study published previously presented a sensitivity analysis for an arbitrarily adopted variability of the transport parameters. The analysis involved examining changes in the shape of breakthrough curves caused by the alteration of each parameter value. Specially defined indicators called descriptors were proposed to quantitatively describe the breakthrough curves. Then, formulas were proposed to determine the percentage deviations of descriptors of the breakthrough curve obtained for the reactive tracer in relation to the descriptors of the breakthrough curve of the conservative tracer. In the work described in this article, the deviations are analyzed and an algorithm is proposed that allows the preselection of the most suitable sorption model out of the five discussed simple (one-site) and six hybrid (two-site) models. The algorithm can facilitate and accelerate the interpretation of column experiments of contaminant transport in a porous medium. An example is provided to illustrate the usability of the proposed algorithm.

Numerical simulation of kinetic interface sensitive tracers in two-phase flow in porous media applied in two-dimensional experimental setups

<p>The newly developed kinetic interface sensitive (KIS) tracers have been the focus of research in the past decade, as a new method to determine the mobile interfacial area between immiscible fluids in porous media. An accurate and reliable interfacial area determination is crucial to several industrial applications and the geoscientific research.</p><p>In this work we investigate the relationship between the concentration breakthrough curves of the KIS tracer, consequently the specific interfacial area and the evolution of the mobile non-wetting-phase front.</p><p>Up to now, such laboratory experiments have been conducted only in columns, quasi-one-dimensional systems. In this study we consider two-dimensional domains filled with porous material where immiscible displacement of water by oil takes place. The presence of heterogenous inclusions leads to perturbations in the fluid interface and causes fingers. By means of numerical modelling we investigate these effects and the results will help as a basis in the design of a new two-dimensional flume setup.</p><p>An analysis is performed for different viscosity ratios, capillary numbers corresponding to different capillary pressure-saturation relationships, injection rates and geometrical heterogeneity. We found that the presence of higher or lower permeability inclusions have a significant but clearly distinct impact on the destruction and/or production of the fluid-fluid interfacial area. Lower permeability inclusions increase the overall area of the front, compared to a decrease in the overall area for higher permeability inclusions. By increasing the interfacial area an increase of the reactive tracer concentration is observed. The mobile interfacial area is evaluated at the front of the saturation profile by using a cut-off value from the saturation profile, and then the area of the mobile concentration of the reactive tracer is calculated.</p>