This paper presents theoretical models of the phase transformation and the change of mechanical properties of oil well cement due to underground carbonation reactions. Application of oil well cement has become common practice in CO₂ underground storage formations. However, the CO₂ stored underground may leak through damaged well cement, and it can cause carbonation reactions which may significantly decrease the mechanical properties of well cement. Extensive research has been conducted by using experimental methods in laboratories to characterize the carbonation reactions of cement underground. However, no theoretical formulations have been developed considering the mechanical properties change due to the carbonation effect. In this paper, the CO₂ profile was predicted first by the error function solution of a 1D CO₂ diffusion equation and further the carbonation reaction rate was calculated. The phase transformation of well cement due to carbonation were then analyzed by using a stoichiometric model. After that, the changes of mechanical properties of well cement were modeled using a two-phase generalized self-consistent model at different scales. Specifically, the decrease of the elastic modulus of well cement during the carbonation process was used as an example application of the model. Finally, the modeling result was validated with published experimental results.

本文提出了由于地下碳化反应引起的油井水泥的相变和力学性能变化的理论模型。在CO ₂地下储层中，油井水泥的应用已成为普遍的做法。但是，储存在地下的CO ₂可能会通过受损的井眼水泥泄漏，并且会引起碳化反应，这可能会大大降低井眼水泥的机械​​性能。通过在实验室中使用实验方法进行了广泛的研究，以表征地下水泥的碳化反应。然而，考虑到由于碳化作用而引起的机械性能变化，尚未开发出理论公式。在本文中，CO ₂首先通过一维CO ₂扩散方程的误差函数解来预测碳原子分布，然后计算碳酸化反应速率。然后使用化学计量模型分析由于碳化引起的井水泥的相变。之后，使用两阶段的广义自洽模型在不同尺度下模拟了井水泥的力学性能变化。具体而言，以碳化过程中井水泥的弹性模量下降为模型的示例应用。最后，通过公开的实验结果验证了建模结果。