Cementitious grouts are a vital component for the economically-viable implementation of the geological storage of CO₂ in providing an engineered long-term seal. In this study a class G cement was carbonated at 80 bar, at either 60 °C or 120 °C, whilst immersed in a synthetic brine for durations of up to 5 months. X-ray computed tomography was used to evaluate the advancement of carbonation depth, whilst SEM/EDXA and XRD were used to characterise microstructural alteration of the cement phases. The microstructure of the ‘main carbonation front’ was found to be representative of the governing reactive transport mechanism. An ill-defined ‘main carbonation front’ during carbonation at 80 bar/60 °C showed a carbonation mechanism controlled by the rate or precipitation/dissolution reactions; diffusion in that case was not the controlling factor. The faster local supersaturation conditions in the pores at 60 °C (with respect to Ca²⁺ and HC$O_3^{-}$) created a dynamic system of aragonite precipitation from the carbonated to the inner regions of the cement. At 80 bar/120 °C a clearly defined ‘main carbonation front’ with higher compositional density than at 60 °C, was correlated with the fast reactions and diffusion limited evolution of the ‘main carbonation front’. Calcite, as the main result of those fast reactions at 120 °C, filled ubiquitously previously unmineralized voids, creating a system less prone to compositional alterations by chemical changes due to the CO₂ plume. This study showed, that the formation of calcium carbonate polymorphs depends on the kinetics of carbonation reactions for a class G cement that is determined by temperature and time. The findings of the current paper can be further used for the understanding of reaction processes within the cements of the CO₂ injection wells and assess their long-term chemical stability.

水泥浆是经济可行地实施 CO ₂地质封存的重要组成部分提供工程化的长期密封。在这项研究中，G 级水泥在 80 巴、60 °C 或 120 °C 下碳酸化，同时浸入合成盐水中长达 5 个月。X 射线计算机断层扫描用于评估碳化深度的进展，而 SEM/EDXA 和 XRD 用于表征水泥相的微观结构变化。发现“主要碳化前沿”的微观结构代表了控制反应传输机制。在 80 bar/60 °C 的碳化过程中，一个不明确的“主要碳化前沿”显示出由速率或沉淀/溶解反应控制的碳化机制；在这种情况下，扩散不是控制因素。60 °C 时孔隙中更快的局部过饱和条件（相对于 Ca ²⁺ 和HC${哦}_3^{-}$）创建了一个从碳酸盐化到水泥内部区域的文石沉淀动态系统。在 80 bar/120 °C 时，一个明确定义的“主碳化前沿”的组成密度高于 60 °C，这与“主碳化前沿”的快速反应和扩散受限演化相关。方解石，作为 120 °C 下这些快速反应的主要结果，填充了无处不在的以前未矿化的空隙，创建了一个不太容易因 CO ₂引起的化学变化而导致成分改变的系统羽。该研究表明，碳酸钙多晶型物的形成取决于由温度和时间决定的 G 级水泥的碳酸化反应动力学。本文的研究结果可进一步用于了解 CO ₂注入井水泥内的反应过程并评估其长期化学稳定性。