非水相液滲透係數-飽和度-毛細壓力關係之微模型 試驗研究

Abstract

非水相液（Non-Aqueous-Phase-Liquid, NAPL）雖然在於水中溶解度很低，惟其在自然界中不易被分解，且部分非水相液具有高毒性。因此，若不慎滲漏入土壤中，將對大環境形成重大威脅。而在探討NAPL在土層中傳輸及宿命的過程中，非水相液於土層中滲透係數、飽和度及毛細壓力的關係曲線為其中關鍵的一環。 傳統在探討相對滲透係數與飽和度關係時，多以砂箱模型實驗。然而砂箱實驗有其不易控制、準確性較低及實驗重複性差等缺點。本研究以可透視微模型，配合數位影像分析觀察多孔界質中多相流的微觀行為，並且取得水、空氣、柴油（LNAPL）和四氯乙烷（DNAPL）各兩相之間的相對滲透係數-飽和度-毛細壓力的關係曲線。使用可透視微模型實驗，其優點在於可清楚的觀察到多孔介質中多相流體的流動機制，配合數位影像分析，更可精確的測量介質中的飽和度。利用雷射雕刻工具，我們可以複製出許多完全相同的多孔介質，以進行多組重複、對照性的實驗。在探討飽和度與毛細壓力關係曲線圖中可發現，水對空氣流體對之實驗與理論值最為吻合，以此流體對應用比例原則推估出的比例值也較能與實驗值符合，相對滲透係數與飽和度關係曲線中亦能與經驗曲線相符合。本研究所取得的實驗數據，並將可進一步做為數值模式之輸入參數，探討此關係曲線對NAPL在土壤中傳輸及宿命之影響。

Although the solubility of Non-Aqueous-Phase-Liquid (NAPL) is low in water, decomposing NAPL in nature is extremely difficult and parts of NAPL are high-toxic. Consequently, the accidental leakage of NAPL into groundwater due to improper storage have threatened the environment. The study of fate and transport process of NAPL in subsurface is an important environmental issue, and the curve of the relation between the permeability, saturation, and capillary pressure of NAPL in the subsurface plays a pivotal role in describing the process. Although the sand tank model is conventionally adopted to examine the relation between permeability and saturation, this model is difficult to control, has a low accuracy, and lacks experience in repeats. This study adopts the perspective micro-model and performs digital image analysis (DIA) to examine the micro-behavior of multiphase flow systems in porous media and obtain the curve of relation between relative permeability, saturation, and capillary pressure between every two phases of water, air, LNAPL, and Tetrachloroethane(DNAPL). The perspective micro-model allows experimenters to clearly observe the multiphase flow systems in porous media. Additionally combining the model with digital image analysis, allows us to precisely measure the saturation of media. Moreover, by using laser tools, a large number of porous media which are identical in all aspects can be reproduced to repeat numerous comparative sets of an experiment. As for the curve that expresses the relation between saturation and capillary pressure, experimental results of water-air flow system corresponds to the theoretical data. Additionally, the proportion derived from the scaling rule is congruous to the experimental data. Moreover, the curve that expresses the relation of the relative permeability and saturation is nearly the same as the experimental curve. Experimental data in this study will go a step further to be the parameters of numerical model that describes how the curve of relation affects NAPL with its fate and transfer process in ground.