Modeling of Gel Barrier Formation by Using Horizontal Wells

Abstract

Barrier systems have recently been employed for contaminant migration control and/or as an integral part of in situ remediation efforts. In this study, we investigate horizontal gel barrier systems constructed by injecting colloidal silica (CS) through horizontal pipes in unsaturated soils. The gel barrier systems are achieved from conversion of a gelling solution to a solid as gelation progresses. The gelation process is initiated in the CS with the addition of electrolytes such as NaCl. The system consisting of a set of horizontal wells is simulated by a vertical two-dimensional mathematical model and the effects of operating parameters and soil properties on emplacement of a CS barrier are evaluated. Laboratory-scale numerical experiments show that an increase in total CS release volume yields a better barrier formation by allowing two gel mixture plumes to merge halfway between each pair of injection pipes thus forming a continuous low-permeability layer between adjacent injection wells. In field-scale numerical experiments, direct correlations between the size of the horizontal gel layer and operating parameters such as the injection pressure head and gel point of the injected CS (a property relevant to NaCl concentration) are observed.