Chemical reactions of carbonate-rich mudstones with aqueous CO2 and their impacts on rock's local microstructural and chemo-mechanical properties
Chemical reactions of carbonate-rich mudstones with aqueous CO2 and their impacts on rock's local microstructural and chemo-mechanical properties
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DOI：
10.1016/j.jngse.2022.104587
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发表时间：
2022-05
影响因子：
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通讯作者：
R. Prakash;Pierre Christian Kana Nguene;A. Noshadravan;S. Abedi
中科院分区：
文献类型：
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作者：
R. Prakash;Pierre Christian Kana Nguene;A. Noshadravan;S. Abedi
对酸性卤水作用下富碳酸盐岩结构完整性的评价，在很大程度上依赖于对岩石化学变化和力学性质改变之间耦合关系的理解。本研究的目的是在高压和高温条件下暴露于富CO2卤水的碳酸盐岩泥岩的综合微尺度化学力学和微结构表征。对X射线显微计算机断层扫描（micro-CT）图像进行数字图像分析，以了解孔隙和不同材料相的微观结构演化和空间分布。这种方法显示了三个不同的孔隙度和碳酸盐含量区域（由碳酸钙的溶解和沉淀引起），这对于理解正在研究的岩石的机械蚀变至关重要。对微CT图像的详细分析还揭示了碳酸钙在平行于流动/反应方向的孔中的优选沉淀。使用耦合网格纳米压痕和扫描电子显微镜-能量色散谱（SEM-EDS）进行的微尺度化学机械测试补充了微CT结果：发现靠近反应表面的溶解区具有较低的硬度和压痕模量，而在相邻的沉淀区观察到增加的值。此外，沉淀带的厚度被发现是相当高的方向上的层面，这需要特别注意的层状岩石，如页岩和泥岩。微尺度区域和层状结构的微观结构和力学性质预计会影响岩石的整体力学性质和完整性。这些结果增强了我们对富碳酸盐岩泥岩在酸性卤水作用下宏观机械蚀变的微观成因的理解。
Assessment of the structural integrity of carbonate-rich rocks subjected to acidic brine strongly relies on the understanding of the coupling between the chemical changes and the alteration of the mechanical properties of rocks. This study aims at an integrated microscale chemo-mechanical and microstructural characterization of carbonate mudstones exposed to CO2-rich brine under high pressure and high temperature conditions. Digital image analysis was performed on X-ray micro-computed tomography (micro-CT) images to realize microstructural evolution and spatial distribution of pores and different material phases. This approach showed three distinct regions of porosity and carbonate content (resulting from dissolution and precipitation of calcium carbonates), which are critical for understanding the mechanical alteration of the rocks being investigated. Detailed analysis of the micro-CT images also revealed the preferred precipitation of calcium carbonates in pores parallel to the flow/reaction direction. Microscale chemo-mechanical testing performed using coupled grid nanoindentation and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) complemented the micro-CT results: dissolution zones close to the reacted surface were found to have lower hardness and indentation modulus while an increased values in adjacent precipitation zones was observed. Also, the thickness of the precipitation zones was found to be considerably higher in the direction of the bedding planes, which needs special attention in laminated rocks like shales and mudstones. The microstructural and mechanical properties of the microscale regions and the layered structure are expected to influence the overall mechanical properties and integrity of the rock. These results enhance our understanding of the microscale origin of the macroscopic mechanical alteration of carbonate-rich mudstones subjected to acidic brine.