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A Pore‐Scale Investigation of Mineral Precipitation Driven Diffusivity Change at the Column‐Scale
Water Resources Research ( IF 5.4 ) Pub Date : 2021-04-22 , DOI: 10.1029/2020wr028483
H. Deng 1 , C. Tournassat 1, 2, 3 , S. Molins 1 , F. Claret 2 , C. I. Steefel 1
Affiliation  

Mineral precipitation affects the pore structure and thus transport properties of porous media. In this study, we investigated the pore‐scale dynamics of precipitation in diffusion controlled systems and the resulting impacts on the effective diffusivity, using a micro‐continuum reactive transport model. Forty two‐dimensional pore structures representing both idealized and realistic geometries were simulated with consideration of different precipitation scenarios and rates. A homogeneous nucleation scenario reproduced patterns observed in previous experimental study showing mixing‐induced precipitation, and a surface growth scenario captured the pattern for mineral precipitation on a substrate with the same or similar mineral structures. In all cases, local precipitation resulted in the reduction in the average porosity of the domain (Φ) until the cessation of diffusive transport and the termination of precipitation. The minimum porosity reached was referred to as the critical porosity (Φc). The effective diffusivity (Deff) decreased with Φ and dropped sharply to effectively zero, that is, the critical effective diffusivity (Deffc), as Φc was reached. These pore‐scale dynamics can be captured by a revised urn:x-wiley:00431397:media:wrcr25282:wrcr25282-math-0001 relationship that explicitly considers the critical porosity and the corresponding effective diffusivity, and the pre‐exponential coefficient and the exponent of the relationship varied with initial pore structure and the precipitation kinetics. Overall, the homogeneous nucleation scenario results in systematically larger Φc and coefficients that give rise to a sharper decrease in diffusivity as Φc is approached, compared to the surface growth scenario. The revised relationship was also implemented at continuum scale and used to examine column scale diffusivity change and reactions.

中文翻译:

柱尺度下矿物沉淀驱动扩散率变化的孔隙尺度研究

矿物沉淀影响孔隙结构,从而影响多孔介质的传输性能。在本研究中,我们使用微连续反应运输模型研究了扩散控制系统中降水的孔隙尺度动力学及其对有效扩散率的影响。考虑到不同的降水情景和速率,模拟了代表理想和实际几何形状的40个二维孔隙结构。均质成核情况再现了先前实验研究中观察到的模式,显示了混合诱发的降水,而表面生长情况则捕获了具有相同或相似矿物结构的基质上矿物沉淀的模式。在所有情况下,局部降水都会导致该区域的平均孔隙度降低(Φ)直到扩散传播停止和沉淀终止。达到最小孔隙率被称为临界孔隙率(Φ Ç)。的有效扩散(d EFF)具有降低的Φ和急剧下降到实际上为零,即,临界有效扩散(d EFF Ç),作为Φ Ç达到。这些孔尺度动力学可以通过修改获得。骨灰盒:x-wiley:00431397:media:wrcr25282:wrcr25282-math-0001该关系明确考虑了临界孔隙度和相应的有效扩散率,并且该关系的指数前系数和指数随初始孔隙结构和沉淀动力学而变化。总体而言,在系统较大均相成核场景结果Φ Ç和系数即导致在扩散性更尖锐下降Φ Ç被接近,相对于表面增长方案。修订后的关系也以连续标度实施,并用于检查色谱柱标度的扩散率变化和反应。
更新日期:2021-05-03
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