Abstract Predicting the solute dispersivity in porous media is complicated by the known scale dependency of dispersion processes. In this study, we combined three complementary methods to investigate solute dispersivity at different length scales. The applied methods included 36-cm long column experiments, extremely large three-dimensional (3D) X-ray image-based pore network simulations, and Darcy scale modelling. We used X-ray imaging to extract the information on pore structures needed to construct a very long, 36-cm, pore network model. Doing so, for the first time, a direct comparison of the pore-scale model to the large experimental observations was performed. The longitudinal dispersivity was found to increase with length, with the rate of increase being lower at higher flow velocities. Results have shown that a pore network, which matches pore connectivity distribution and pore size distribution of a sub-sample of the column, is able to reproduce the experimentally observed solute breakthrough curves. Pore-scale modelling provided the extent of pore velocity variations corresponding to various locations along the experimental column as well as the one dimensional (1D) Darcy scale model. We have found that even in homogenous porous media immobile pores exist, with low velocities compared to the average velocity, which creates local concentration maximals.

中文翻译：

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饱和砂柱溶质纵向弥散度的大规模孔隙网络和连续介质模拟

摘要 由于分散过程的已知尺度依赖性，预测多孔介质中的溶质分散性变得复杂。在这项研究中，我们结合了三种互补的方法来研究不同长度尺度的溶质分散性。应用的方法包括 36 厘米长的柱子实验、基于超大三维 (3D) X 射线图像的孔隙网络模拟和达西比例模型。我们使用 X 射线成像来提取构建非常长的 36 厘米孔隙网络模型所需的孔隙结构信息。这样做，首次将孔隙尺度模型与大型实验观察进行了直接比较。发现纵向弥散率随着长度的增加而增加，在较高的流速下增加的速率较低。结果表明，一个孔隙网络，与色谱柱子样品的孔连通性分布和孔径分布相匹配，能够重现实验观察到的溶质穿透曲线。孔隙尺度建模提供了对应于沿着实验柱的不同位置的孔隙速度变化范围以及一维 (1D) 达西尺度模型。我们发现，即使在均质多孔介质中也存在固定孔隙，与平均速度相比速度较低，这会产生局部浓度最大值。孔隙尺度建模提供了对应于沿着实验柱的不同位置的孔隙速度变化范围以及一维 (1D) 达西尺度模型。我们发现，即使在均质多孔介质中也存在固定孔隙，与平均速度相比速度较低，这会产生局部浓度最大值。孔隙尺度建模提供了对应于沿着实验柱的不同位置的孔隙速度变化范围以及一维 (1D) 达西尺度模型。我们发现，即使在均质多孔介质中也存在固定孔隙，与平均速度相比速度较低，这会产生局部浓度最大值。