A general model of radial dispersion with wellbore mixing and skin effects

Abstract

The mechanism of radial dispersion is essential for understanding reactive transport in the subsurface and for estimating the aquifer parameters required in the optimization design of remediation strategies. Many previous studies demonstrated that the injected solute firstly experienced a mixing process in the injection wellbore, then entered a skin zone after leaving the injection wellbore, and finally moved into the aquifer through advective, diffusive, dispersive, and chemical-biological-radiological processes. In this study, a physically based new model and the associated analytical solutions in the Laplace domain are developed by considering the mixing effect, skin effect, scale effect, aquitard effect, and media heterogeneity (in which the solute transport is described in a mobile-immobile framework). This new model is tested against a finite-element numerical model and experimental data. The results demonstrate that the new model performs better than previous models of radial dispersion in interpreting the experimental data. To prioritize the influences of different parameters on the breakthrough curves, a sensitivity analysis is conducted. The results show that the model is sensitive to the mobile porosity and wellbore volume, and the sensitivity coefficient of the wellbore volume increases with the well radius, while it decreases with increasing distance from the wellbore. The new model represents the most recent advancement in radial dispersion study, incorporating many essential processes not considered in previous investigations.