IMPROVING SWEEP EFFICIENCY AND DELIVERY OF OXIDANTS TO LOW PERMEABILITY ZONES USING VISCOSIFYING AGENTS

In situ chemical oxidation (ISCO) is a favorable method of remediation which involves injecting chemical oxidants into the subsurface to degrade contaminants in place rather than excavating and remediating contaminated soil and groundwater ex situ. While laboratory studies have shown ISCO to be successful at achieving near-complete degradation of contaminants, applications in the field have not been as effective due to subsurface heterogeneity. One approach to reducing the impacts of heterogeneity is to co-inject oxidant solutions and polymers to increase the viscosity of the ISCO fluid. The increased viscosity increases local pressure gradients and thus improves flow to zones of low permeability. There remains an uncertainty as to whether the most commonly used polymers are in fact the best options. Past environmental applications have typically utilized food-grade polymers, such as xanthan (XG) and guar (GG) gums, in order to minimize ecological and human health impacts. Laboratory studies indicate that XG is compatible with oxidants for contaminant degradation, and that the addition of polymers has an acceptably low impact on contaminant degradation rates. XG, however, exhibits shear-thinning non-Newtonian behavior, which is expected from a theoretical standpoint to be less efficient in improving sweep efficiency than Newtonian and shear-thickening fluids. Because the relative efficiency of various fluid rheologies has not been experimentally tested, here we begin to investigate the feasibility of improving sweep efficiency of the ISCO fluid with alternative polymer additives. We have characterized a suite of additives in terms of rheology and oxidant compatibility and developed a method to determine hydraulic conditions associated with the flow of polymer solutions through porous media. The results of this work are being used to inform the design of future experiments involving two-dimensional flow of optimized ISCO fluids, which will in turn be used to optimize field-ready ISCO fluids.