Recent research has demonstrated that CO₂, working as a fracturing fluid, possesses unique advantages during shale reservoirs development. Since water may exist in formations or be introduced into formations during drilling, carbonic acid would form after CO₂’s dissolution into water. In this study, modification of microscopic surface properties of shale induced by carbonic acid treatment is comprehensively studied. Based on scanning electron microscope (SEM) imaging and energy dispersive spectrometer (EDS) mapping, the elemental evolution in the same position illustrates a certain correlation between the microstructure change and the dissolution of calcite and dolomite. Adhesion properties of the shale surface are revealed by atomic force microscopy (AFM). Adhesion force remains relatively stable for the quartz regions and it shows an irregular increase in the nonquartz regions after carbonic acid treatment. Stereo images obtained by a confocal microscope show that the surface becomes smoother after carbonic acid treatment despite the formation of dissolution cavities. According to nanoindentation tests, Young’s modulus and hardness are significantly reduced and the shale sample becomes more ductile after acid treatment. These findings provide a deep insight into the microscale alterations in the shale surface induced by carbonic acid treatment, which contributes to the further assessment of CO₂-based fracturing and CO₂ sequestration.

中文翻译：

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碳酸处理对页岩微观性质的改性：对基于CO ₂压裂的页岩地层的影响

最近的研究表明，作为压裂液的CO ₂在页岩油藏开发过程中具有独特的优势。由于水可能存在于地层中或在钻井过程中被引入地层中，因此在CO ₂排放后会形成碳酸溶于水。在这项研究中，全面研究了碳酸处理引起的页岩微观表面性质的改变。基于扫描电子显微镜（SEM）成像和能量色散谱仪（EDS）映射，同一位置的元素演化说明了微观结构变化与方解石和白云石溶解之间存在一定的相关性。页岩表面的粘附特性通过原子力显微镜（AFM）揭示。对于石英区域，粘附力保持相对稳定，并且在碳酸处理后，非石英区域的粘附力显示出不规则的增加。通过共聚焦显微镜获得的立体图像显示，尽管形成了溶蚀腔，但在碳酸处理后表面仍变得更光滑。根据纳米压痕测试，酸处理后，杨氏模量和硬度显着降低，页岩样品的延展性更高。这些发现提供了对碳酸处理引起的页岩表面微观变化的深刻了解，这有助于进一步评估CO。基于₂的压裂和CO ₂隔离。