Polymer solution injection has emerged as a promising method for the remediation of NAPL (non-aqueous phase liquids)-contaminated aquifers. This technique enhances recovery efficiency by modifying viscous forces, stabilizing the displacement front, and minimizing channeling effects. However, there remains a significant gap in understanding the behavior of polymer solutions, particularly those with different molecular weights (MW), for mobilizing DNAPL (dense non-aqueous phase liquids) trapped in heterogeneous aquifers, especially within low-permeability layers. In this study, we address this gap by investigating the mobilization of DNAPL lenses confined by low-permeability layers through the injection of polyethylene oxide (PEO) polymers of varying MW. PEO solutions with MW of 5 M (million) and 8 Mg/mol displayed shear-thinning behavior for shear rates of 0.01 to 100 s^-1, while the 1 Mg/mol solution showed shear-thinning below 10 s^-1 and Newtonian behavior above. PEO solutions in porous media exhibit Newtonian behavior at low-to-moderate shear rates for all MWs, likely due to confinement-limited entanglement.Adsorption studies found non-significant PEO adsorption on soil surfaces, likely due to its large molecular size. Post-flushing of PEO-saturated columns with water led to notable permeability reductions attributed to viscous fingering. Column tests indicated a decrease of the residual DNAPL saturation with the capillary number (Ca), more sharply in low permeability soils.2D cell tests identified three stages of DNAPL mobilization: initial stabilization, sharp recovery increase upon PEO arrival, and a final stabilization at residual saturation. The duration of each transition was found to be influenced by concentration. Numerical simulations accurately mirrored these stages and provided additional insights into PEO viscosity distribution and DNAPL mobilization patterns in heterogeneous media. The results highlighted that higher injection rates promote mobilization from the two low permeability layers surrounding the DNAPL bank from both sides and the upper zone, while lower rates mainly drive mobilization from the upper side. Using numerical simulations the performance of PEO injection on displacement of DNAPL in multiple lenses and various position of recovery points was evaluated.

中文翻译：

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使用剪切稀化 PEO 聚合物在非均质含水层中移动 DNAPL 透镜：实验和数值研究


聚合物溶液注入已成为修复 NAPL（非水相液体）污染含水层的一种很有前途的方法。该技术通过修改粘性力、稳定位移前沿和最小化沟流效应来提高恢复效率。然而，在了解聚合物溶液的行为方面仍然存在很大差距，尤其是那些具有不同分子量 （MW） 的聚合物溶液，用于移动被困在非均质含水层中的 DNAPL（致密非水相液体），尤其是在低渗透层中。在这项研究中，我们通过研究通过注射不同 MW 的聚环氧乙烷 （PEO） 聚合物来移动受低渗透层限制的 DNAPL 透镜，从而解决了这一差距。MW 为 5 M（百万）和 8 Mg/mol 的 PEO 溶液在 0.01 至 100 ^s-1 的剪切速率下表现出剪切稀化行为，而 1 Mg/mol 溶液在 10 s-1 以下表现出剪切稀化，在高于 10 ^s-1 时表现出牛顿行为。对于所有 MW，多孔介质中的 PEO 溶液都表现出低到中等剪切速率的牛顿行为，这可能是由于约束限制的纠缠。吸附研究发现土壤表面的 PEO 吸附不明显，这可能是由于其分子尺寸大。用水冲洗 PEO 饱和的色谱柱后，由于粘性指法导致渗透率显著降低。柱测试表明，在低渗透性土壤中，残余 DNAPL 饱和度随毛细管数 （Ca） 的降低而降低得更剧烈.2D 细胞测试确定了 DNAPL 动员的三个阶段：初始稳定、PEO 到达时恢复急剧增加和残余饱和度的最终稳定。发现每个转变的持续时间都受浓度的影响。 数值模拟准确地反映了这些阶段，并为非均质介质中的 PEO 粘度分布和 DNAPL 动员模式提供了更多见解。结果强调，较高的注入速率促进了 DNAPL 组周围两个低渗透层从两侧和上部区域的动员，而较低的注入速率主要驱动上部的动员。使用数值模拟评估了 PEO 注射对 DNAPL 在多个晶状体中置换和恢复点不同位置的性能。