Quantitative analysis of dominant mechanisms in improving fluid sweeping uniformity in a layered heterogeneous system...

Although it has been proven that the addition of shear-thinning polymers can lead to an improvement in the sweeping efficiency of the remedial agent in heterogeneous aquifers, the related mechanisms require further investigation. This study revealed the mechanisms associated with the improvement of fluid sweeping uniformity. Under the assumption of no transverse flow existed between layers, the variation patterns of the fluid sweeping uniformity in strip layered heterogeneous media (R_P/R_K) with the change of the fluid hydraulic conductivity were investigated. The outcomes showed that, for the hydraulic conductivity dominated fluid sweeping uniformity control, the performance was satisfactory only when the ratio of the hydraulic conductivities of viscous fluid in porous media (PM) layers (K_1P/K_2P) is less than 2.5 times that of pure oxidant solution (K_1K/K_2K), and PM combinations with higher permeability contrast usually present a wider applicability and better performance. In addition, transverse fluid movement was more likely to occur in layers with low permeability contrasts (2.3-5) than in those with relatively higher permeability contrasts (> 11). The observed transverse pressure difference directly confirmed the hypothesis of the dynamics of the cross-flow mechanism that existed during viscous fluid flow, and the relationships between the fluid fronts and the pressure head difference at each point (Px) were proposed. Our study exemplifies an effective strategy for determining the most economically effective co-injection concentration of xanthan to achieve highly efficient delivery of remedial agents.