溶解碳酸盐时反应表面积的瞬间增加
Momentary increase in reactive surface area in dissolving carbonate
摘要：
矿物和反应流体之间的表面积的量化是必不可少的环境应用的反应输运模拟。这个量随着微观结构的变化而变化，并且很难预测，因为反应表面的产生和破坏机制仍然难以捉摸。在数值模拟中考虑天然多孔介质固有的非均匀性的挑战进一步使问题复杂化。在这里，我们首先显示了直接观察反应性表面生成白垩在circumneutral碱性pH值下使用原位X射线显微断层扫描。反应性表面积的瞬间增加不能用流体可及性的变化或矿物学异质性引起的表面粗糙化来解释。然后，我们结合灰度nanotomography数据与数值模拟表明，类似的时间行为可以观察到在很宽的pH值范围内的多孔介质溶解在施加的流场。我们属性的观察流体流动和矿物溶解之间的耦合，并认为，表面生成的程度是强烈相关的平流渗透深度的反应物。最后，我们证明了使用宏观Damköhler数作为现象的指标的适用性，并讨论了地质碳储量以外的环境意义。
英文摘要：
The quantification of surface area between mineral and reactive fluid is essential in environmental applications of reactive transport modelling. This quantity evolves with microstructures and is difficult to predict because the mechanisms for the generation and destruction of reactive surface remain elusive. The challenge of accounting for the inherent heterogeneities of natural porous media in numerical simulation further complicates the problem. Here we first show a direct observation of reactive surface generation in chalk under circumneutral to alkaline pH using in situ X-ray microtomography. The momentary increase of reactive surface area cannot be explained by a change in fluid accessibility or by surface roughening stemming from mineralogical heterogeneity. We then combine greyscale nanotomography data with numerical simulations to show that similar temporal behaviour can be observed over a wide range of pH as porous media dissolve in imposed flow field. We attribute the observation to the coupling between fluid flow and mineral dissolution and argue that the extent of surface generation is strongly correlated with the advective penetration depth of reactants. To conclude, we demonstrate the applicability of using a macroscopic Damköhler number as an indicator for the phenomenon and discuss its environmental significance beyond geologic carbon storage.
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