BRGM (French Geological Survey), Orléans, France; HydroSciences Montpellier, Université de Montpellier, CNRS, IMT, IRD, Montpellier, France.
BRGM (French Geological Survey), Orléans, France.
J Contam Hydrol. 2023 May;256:104183. doi: 10.1016/j.jconhyd.2023.104183. Epub 2023 Apr 21.
Light Non-Aqueous Phase Liquid (LNAPL) flow on the water table is highly mobile and is sensitive to the fluctuation of groundwater. This process is highly complex and involves the migration of three immiscible phases (i.e. water, LNAPL and air) which need the explicit definition of multiple parameters. A coupled experimental and numerical simulation methodology is performed by using Time Domain Reflectrometer (TDR) and multiphase simulation of a controlled environment to mimic the water table fluctuation and its effect on the LNAPL residual saturation. TDR probes are installed in different locations of a 2D tank (i.e. a cuboid box with relatively low off-plane thickness) and the bulk permittivity of the phases are measured through artificially imposed boundary conditions. The bulk permittivity is then translated into saturation of the three different phases. The translated residual saturations along with the previously measured porous media properties (e.g. porosity and saturated permeability) are then inserted into the numerical simulator (i.e. COMSOL Multiphysics®) and the migration of the three phase in porous media is simulated. The numerical exponents and entry pressures needed for the simulation of the multiphase flow are estimated using the temporal experimental values. The exponents of water LNAPL relative permeability were estimated to be around 2 while the exponents gas LNAPL relative permeability were estimated to be closer to 3. The results, simulated with the optimized parameters, are then evaluated with pictures taken from the transparent face of the 2D tank different stages of the experiment. The temporal evolution of different phase saturation has been compared and validated between the experimental results obtained and interpreted by the TDR probe measurements and the simulations. The relative error stays in the 5 % confidence level for most reported points and only in the highly dynamic flow time steps the error reaches around 12% which are discussed in the text and is accepted due to the highly nonlinear nature of the problem.
非水相液体（LNAPL）在地下水面上的流动具有高度的流动性，并且对地下水的波动敏感。这个过程非常复杂，涉及到三种不混溶相（即水、LNAPL 和空气）的迁移，需要明确定义多个参数。本研究采用时域反射仪（TDR）和多相模拟控制环境的方法，对地下水面波动及其对 LNAPL 残余饱和度的影响进行了实验和数值模拟。TDR 探头安装在二维水箱（即相对低平面厚度的长方体盒）的不同位置，通过人为施加的边界条件测量各相的体介电常数。然后，将体介电常数转换为三个不同相的饱和度。转换后的残余饱和度以及之前测量的多孔介质特性（例如孔隙度和饱和渗透率）被插入到数值模拟器（即 COMSOL Multiphysics®）中，模拟三相在多孔介质中的迁移。使用时间实验值估计模拟多相流所需的数值指数和进入压力。水 LNAPL 相对渗透率的指数估计约为 2，而气 LNAPL 相对渗透率的指数估计更接近 3。使用优化后的参数模拟的结果，然后与实验不同阶段从二维水箱透明面拍摄的图片进行评估。通过 TDR 探头测量和模拟获得的实验结果和解释，比较和验证了不同阶段的不同相饱和度的时间演化。在大多数报告的点，相对误差保持在 5%置信水平内，只有在高度动态的流动时间步，误差达到约 12%，这在文本中进行了讨论，并由于问题的高度非线性而被接受。
