Fractures along interfaces between host rock and wellbore cement have long been identified as potential CO₂ leakage pathways from subsurface CO₂ storage sites. As a consequence, cement alteration due to exposure to CO₂ has been studied extensively to assess wellbore integrity. Previous studies have focused on the changes to either chemical or mechanical properties of cement upon exposure to CO₂-enriched brine, but not on the effects of loading conditions. This paper aims to correct this deficit by considering the combined effects of the fracture pathway and changing effective stress on chemical and mechanical degradation at conditions relevant to geologic carbon storage. Flow-through experiments on fractured cores composed of cement and tight sandstone caprock halves were conducted to study the alteration of cement due to exposure to CO₂-enriched brine at 3, 7, 9, and 12 MPa effective stress. We characterized relevant reactions via solution chemistry; fracture permeability via changes to differential pressure; mechanical changes via micro-hardness testing, and pore structure changes via x-ray tomography. This study showed that the nature and the rates of the chemical reactions between cement and CO₂ were not affected by the effective stress. The differences in the permeability responses of the fractures were attributed to interactions among the geometry of the flow path, the porosity increase of the reacted cement, and the mechanical deformation of reacted asperities. The suite of observed chemical reactions contributed to change in cement mechanical properties. Compared to the unreacted cement, the average hardness of the amorphous silica and depleted layers was decreased while the hardness of the calcite layer was increased. Tomographic imaging showed that preferential flow paths formed in some of the core-flood experiments, which had a significant impact on the permeability response of the fractured samples. We interpreted the observed permeability responses in terms of competition between dissolution of cement phases (leading to enhanced permeability) and mechanical deformation of reacted regions (leading to reduced permeability).

长期以来，沿基质岩石和井眼水泥之间的界面破裂一直被认为是来自地下CO ₂储存位点的潜在CO ₂泄漏途径。结果，已经广泛研究了由于暴露于CO ₂而引起的水泥蚀变以评估井眼完整性。先前的研究集中于暴露于CO _2时水泥化学或机械性能的变化-富含盐水，但不受装载条件的影响。本文旨在通过考虑断裂路径和在与地质碳储量有关的条件下改变有效应力对化学和机械降解的综合作用来纠正这一缺陷。进行了由水泥和致密的砂岩盖岩半块组成的裂隙岩心的流通试验，以研究在3、7、9和12 MPa有效应力下暴露于富含CO _2的盐水引起的水泥变化。我们通过溶液化学表征了相关的反应；通过改变压差来实现裂缝渗透性；通过显微硬度测试改变机械性能，通过X射线断层摄影术改变孔隙结构。这项研究表明，水泥与一氧化碳之间化学反应的性质和速率_2个不受有效压力的影响。裂缝渗透率响应的差异归因于流动路径的几何形状之间的相互作用，反应后水泥的孔隙率增加以及反应后凹凸面的机械变形。一系列观察到的化学反应有助于改变水泥的机械​​性能。与未反应的水泥相比，无定形二氧化硅和贫化层的平均硬度降低，而方解石层的硬度增加。层析成像显示，在某些岩心驱替实验中形成了优先流动路径，这对裂缝样品的渗透率响应有重大影响。