Relevance of local compound-specific transverse dispersion for conservative and reactive mixing in heterogeneous porous media
Relevance of local compound-specific transverse dispersion for conservative and reactive mixing in heterogeneous porous media
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DOI：
10.1029/2010wr010270
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发表时间：
2011-07-22
影响因子：
5.4
通讯作者：
Rolle, Massimo
中科院分区：
文献类型：
--
作者：
Chiogna, Gabriele;Cirpka, Olaf A.;Rolle, Massimo
不同的稀释措施已被提出来描述溶质在非均质多孔介质中的混合。这些方法中的大多数导致有效色散系数的定义。为了量化混合，这些放大的参数应该考虑局部尺度分散和非均质地层中流动变化的影响（例如，在高电导率中流动聚焦，而在低电导率夹杂物中流动散焦）。混合的正确量化对于经历反应的化合物的运输特别重要。最近的多示踪剂实验室实验结果表明，在很宽的流速范围内的分子扩散的局部横向分散的依赖性，这意味着化合物特定的横向混合，即使在中间和高的Peclet数。本研究的目的是评估的相关性的化合物特定的局部规模的横向分散保守和反应混合在非均质领域在现场规模。我们限制我们的分析，以稳定状态的二维流动和运输与连续注入线源。我们提出的数值模拟在非均质域的电导率场的变化具有不同的特点，并适用于溶质混合的措施：（1）由二阶中心空间矩导出的有效横向弥散系数，（2）由通量相关的二阶中心空间矩导出的弥散系数，（3）标量耗散率，以及（4）从通量相关稀释指数导出的分散系数。结果表明，化合物特定的横向混合行为也在现场规模，这是特别重要的情况下，低到中等非均质多孔介质。此外，我们表明，在通量相关框架中计算的稀释措施导致混合过程的量化得到改善，并允许定义放大参数（即，有效横向色散系数）受到低程度的不确定性的影响。对于混合控制的反应运输，我们说明了依赖于化合物的反应性溶质羽流的长度上的局部效应的重要性。
Different measures of dilution have been proposed to describe solute mixing in heterogeneous porous media. Most of these approaches lead to the definition of effective dispersion coefficients. In order to quantify mixing, these up-scaled parameters should account for both local-scale dispersion and effects of flow variability in heterogeneous formations (e.g., flow focusing in high-conductivity and defocusing in low-conductivity inclusions). The correct quantification of mixing is particularly important for transport of compounds undergoing reactions. Recent results of multitracer laboratory experiments showed a dependency of local transverse dispersion on molecular diffusion over a wide range of flow velocities, implying compound-specific transverse mixing even at intermediate and high Peclet numbers. The goal of this study is to assess the relevance of a compound-specific local-scale transverse dispersion on conservative and reactive mixing in heterogeneous domains at the field scale. We restrict our analysis to steady state two-dimensional flow and transport with continuous injection from a line source. We present numerical simulations in heterogeneous domains with different characteristics of variability in the conductivity field, and apply as measures of solute mixing: (1) the effective transverse dispersion coefficient derived from second central spatial moments, (2) a dispersion coefficient derived from flux-related second central spatial moments, (3) the scalar dissipation rate, and (4) a dispersion coefficient derived from the flux-related dilution index. The results indicate compound-specific transverse mixing behavior also at the field scale which is particularly significant in case of low to moderately heterogeneous porous media. Moreover, we show that measures of dilution calculated in a flux-related framework result in an improved quantification of mixing processes and allow to define up-scaled parameters (i.e., effective transverse dispersion coefficients) affected by a low degree of uncertainty. For mixing-controlled reactive transport we illustrate the importance of compound-dependent local effects on the length of reactive solute plumes.