Salt deposition has been encountered in near-wellbore regions of saline reservoirs during field-scale carbon dioxide (CO₂) sequestration. To explain this phenomenon, pore-scale studies, mostly in the form of micromodel visualizations, have been previously implemented. However, there is limited knowledge about salt deposition and inherent dynamics in reservoir rocks. This study investigates and characterizes the pore-scale evolution of salt precipitation in natural sandstone and carbonate rocks at conditions prevalent in deep saline aquifers. Using x-ray micro-tomography imaging techniques, three evolution stages – advection-dominated, transition, and diffusion-dominated evaporative drying – are delineated. We provide direct evidence for a new mechanism that occurs during the transition from advection to diffusion-limited flow called reverse solute diffusion. This is typified by upward solute diffusion from regions of lower concentrations within the aqueous phase to the highly concentrated evaporating front. Salt deposits eventually form due to solute accumulation at the brine/supercritical CO₂ interface. The time and extent of precipitation are influenced by CO₂ injection rate and morphological heterogeneity. Specifically, a higher injection rate increases the rapidity of precipitation but causes lower salt deposition. Furthermore, less precipitates form as systems become more homogeneous for the same injection rate. These relationships directly correlate with porosity reduction, leading to a gradual but higher degree of pore plugging in heterogeneous systems.

在现场规模的二氧化碳 (CO ₂) 封存。为了解释这种现象，以前已经实施了孔隙尺度研究，主要以微模型可视化的形式。然而，关于储层岩石中盐沉积和内在动力学的知识有限。本研究调查并表征了在深部咸水层普遍存在的条件下天然砂岩和碳酸盐岩中盐析出的孔隙尺度演化。使用 X 射线显微断层扫描成像技术，描绘了三个演化阶段——平流主导、过渡和扩散主导的蒸发干燥。我们提供了一种新机制的直接证据，该机制发生在从平流到扩散受限流的过渡过程中，称为反向溶质扩散。这是典型的溶质从水相中较低浓度的区域向上扩散到高度浓缩的蒸发前沿。由于盐水/超临界 CO 处的溶质积累最终形成盐沉积物₂界面。沉淀的时间和程度受CO ₂注入速率和形态非均质性的影响。具体而言，较高的注入速率会增加沉淀的速度，但会导致较低的盐沉积。此外，随着系统在相同注入速率下变得更加均匀，形成的沉淀物更少。这些关系与孔隙率降低直接相关，导致非均质系统中孔隙堵塞逐渐但程度更高。