Abstract This paper explores the effect of permeable grain boundaries on carbonate rock dissolution in order to improve our understanding of grain detachment and migration during reactive flow. To do so we investigated the effects of grain size and enhanced reactivity along grain boundaries on global dissolution kinetics. Variations of permeability and porosity were calculated, and exponential relationships were observed in fractured rocks. Our model employed a reactive transport framework based on the Darcy-Brinkman equation to simulate calcite dissolution in carbonate rocks composed of microporous grains and, included fluid transport along grain boundaries. The model includes fluid flow, solute transport by advection–diffusion, heterogeneous reaction between fluid and minerals and grain detachment with subsequent grain transport in macropores. The migration of solid particles due to dissolution was based on cluster analysis and local movement, and the results show that grain detachment can lead to significant decreases in permeability due to the clogging of transport pathways. Microporous media with smaller grain sizes (fine grains in this study) showed a higher average reaction rate than those with coarser grains. In addition, as the overall rates of geochemical processes are commonly affected by the presence of texture heterogeneities such as fractures, a single fracture (macropore) introduced into a microporous matrix composed of permeable grains and grain boundaries was modelled as a large channel connecting the inlet and outlet of the simulation domain. It was found that macropore clogging by grain detachment temporary decreased permeability, lowering the long-term global reaction rates. We also observed that increases in flow rate can reduce detachment and fracture clogging by reducing local dissolution along grain boundaries.

中文翻译：

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具有可渗透晶界的碳酸盐岩矿物溶解过程中的颗粒脱落和输运堵塞

摘要 本文探讨了渗透性晶界对碳酸盐岩溶解的影响，以提高我们对反应流过程中颗粒脱离和迁移的理解。为此，我们研究了晶粒尺寸和沿晶界增强的反应性对整体溶解动力学的影响。计算渗透率和孔隙度的变化，并在裂隙岩石中观察到指数关系。我们的模型采用基于 Darcy-Brinkman 方程的反应输运框架来模拟方解石在由微孔颗粒组成的碳酸盐岩中的溶解，包括沿晶界的流体输运。该模型包括流体流动、通过平流扩散的溶质传输、流体和矿物之间的非均质反应以及颗粒脱离以及随后在大孔隙中的颗粒传输。由于溶解引起的固体颗粒的迁移是基于聚类分析和局部运动，结果表明，由于运输通道的堵塞，颗粒脱离会导致渗透率显着降低。具有较小晶粒尺寸（本研究中为细晶粒）的微孔介质比具有粗晶粒的微孔介质显示出更高的平均反应速率。此外，由于地球化学过程的总体速率通常受到结构异质性（如裂缝）的影响，将单个裂缝（大孔隙）引入由可渗透颗粒和晶界组成的微孔基质中，被建模为连接入口的大通道和模拟域的出口。发现颗粒脱离造成的大孔堵塞暂时降低了渗透率，降低长期的全球反应速度。我们还观察到，流速的增加可以通过减少沿晶界的局部溶解来减少脱离和裂缝堵塞。