Boyd Glen R, Li Minghua, Husserl Johana, Ocampo-Gómez Ana M
Tulane University, Department of Civil and Environmental Engineering, 6823 St. Charles Avenue, New Orleans, Louisiana 70118, USA.
J Contam Hydrol. 2006 Jan 10;82(3-4):319-37. doi: 10.1016/j.jconhyd.2005.10.007. Epub 2005 Nov 21.
A two-dimensional (2D) laboratory model was used to study effects of gravity on areal recovery of a representative dense non-aqueous phase liquid (DNAPL) contaminant by an alcohol pre-flood and co-solvent flood in dipping aquifers. Recent studies have demonstrated that injection of alcohol and co-solvent solutions can be used to reduce in-situ the density of DNAPL globules and displace the contaminant from the source zone. However, contact with aqueous alcohol reduces interfacial tension and causes DNAPL swelling, thus facilitating risk of uncontrolled downward DNAPL migration. The 2D laboratory model was operated with constant background gradient flow and a DNAPL spill was simulated using tetrachloroethene (PCE). The spill was dispersed to a trapped, immobile PCE saturation by a water flood. Areal PCE recovery was studied using a double-triangle well pattern to simulate a remediation scheme consisting of an alcohol pre-flood using aqueous isobutanol ( approximately 10% vol.) followed by a co-solvent flood using a solution of ethylene glycol (65%) and 1-propanol (35%). Experiments were conducted with the 2D model oriented in the horizontal plane and compared to experiments at the 15 degrees and 30 degrees dip-angle orientations. Injection was applied either in the downward or upward direction of flow. Experimental results were compared to theoretical predictions for flood front stability and used to evaluate effects of gravity on areal PCE recovery. Sensitivity experiments were performed to evaluate effects of the alcohol pre-flood on PCE areal recovery. For experiments conducted with the alcohol pre-flood and the 2D model oriented in the horizontal plane, results indicate that 89-93% of source zone PCE was recovered. With injection oriented downward, results indicate that areal PCE recovery was 70-77% for a 15 degrees dip angle and 57-59% for a 30 degrees dip angle. With injection oriented upward, results indicate that areal PCE recovery was 57-60% at the 30 degrees dip angle, which was similar to PCE recovery for injection in the downward flow direction. Lower areal PCE recovery at greater dip angles in either direction of flow was attributed to DNAPL swelling and migration, flood front instabilities and bypassing of the displaced fluid past the extraction wells during the alcohol pre-flood. Additional results demonstrate that the use of an alcohol pre-flood can be beneficial in improving DNAPL recovery in the horizontal orientation, but pre-flooding may reduce areal recovery efficiency in dip-angle orientations. This study also demonstrates the use of theoretical perturbation (fingering) analysis in predicting NAPL recovery efficiency for flooding processes in remediating aquifers with dip angles.
使用二维（2D）实验室模型研究重力对在倾斜含水层中通过醇预冲洗和共溶剂冲洗对代表性致密非水相液体（DNAPL）污染物进行面积回收的影响。最近的研究表明，注入醇和共溶剂溶液可用于原位降低DNAPL球粒的密度并将污染物从源区驱替出来。然而，与醇水溶液接触会降低界面张力并导致DNAPL膨胀，从而增加DNAPL不受控制地向下迁移的风险。二维实验室模型在恒定的背景梯度流条件下运行，使用四氯乙烯（PCE）模拟DNAPL泄漏。通过水驱将泄漏物分散到捕获的、不流动的PCE饱和度。使用双三角形井网研究PCE的面积回收，以模拟一种修复方案，该方案包括先用异丁醇水溶液（约10%体积）进行醇预冲洗，然后用乙二醇（65%）和1-丙醇（35%）的溶液进行共溶剂冲洗。实验在二维模型水平放置时进行，并与在15度和30度倾角放置时的实验进行比较。注入方向为向下或向上流动方向。将实验结果与驱替前沿稳定性的理论预测进行比较，并用于评估重力对PCE面积回收的影响。进行敏感性实验以评估醇预冲洗对PCE面积回收的影响。对于在水平放置的二维模型下进行的醇预冲洗实验，结果表明源区89 - 93%的PCE被回收。当注入方向向下时，结果表明在15度倾角下PCE的面积回收为70 - 77%，在30度倾角下为57 - 59%。当注入方向向上时，结果表明在30度倾角下PCE的面积回收为57 - 60%，这与向下流动方向注入时的PCE回收相似。在任一流动方向上，倾角越大PCE的面积回收越低，这归因于DNAPL的膨胀和迁移、驱替前沿的不稳定性以及在醇预冲洗过程中被驱替流体绕过抽提井。其他结果表明，使用醇预冲洗在水平方向上有利于提高DNAPL的回收，但预冲洗可能会降低倾角方向上的面积回收效率。本研究还展示了使用理论扰动（指进）分析来预测在修复有倾角的含水层中驱替过程的NAPL回收效率。
