To better implement super critical carbon dioxide (SC-CO₂) fracturing on shale, it is important to investigate effects of SC-CO₂ on rock mechanical properties. Because micro-scale mechanical properties determine the overall mechanical response, the determination of micro-scale mechanical properties is necessary. In this paper, continuous stiffness measurement (CSM) and constant loading rate (CLR) mode nanoindentation was performed on shale samples before and after SC-CO₂ treatment. With the aid of scanning electron microscope and energy dispersive spectra mapping technique, mechanical strength difference on clay-rich and quartz –rich areas in shale sample can be identified. The results demonstrated that samples treated by SC-CO₂ present lower Hardness, Young’s modulus and fracture toughness. The average decrease rates of hardness and Young’s modulus under CSM mode for three sample are 32.01 % and 11.75 %. The hardness, Young’s modulus and fracture toughness under CLR mode for the three samples have decreased at average rates of 29.5 %, 11.0 %, and 11.3 %, respectively. Moreover, the mechanical strength substantially decreases in the clay-rich area because CO₂ adsorption and mineral dissolution happen after the SC-CO₂ treatment. The change in mechanical properties in quartz-rich area is much smaller because there is little effect on quartz. The close examination of indentation fracture geometry indicate more micro fractures have been generated in the post SC-CO₂ treated shale, thus we can expect the capability of SC-CO₂ for rock weaken. This study can provide more insights for fracture mechanism in target areas with different mineral distribution, which is beneficial for SC-CO₂ engineering applications.

为了更好地在页岩上进行超临界二氧化碳（SC-CO ₂）压裂，研究SC-CO ₂对岩石力学性能的影响非常重要。由于微观机械性能决定了总体机械响应，因此必须确定微观机械性能。在本文中，在SC-CO ₂处理之前和之后对页岩样品进行了连续刚度测量（CSM）和恒定加载速率（CLR）模式纳米压痕。借助扫描电子显微镜和能量色散谱图绘制技术，可以确定页岩样品中富含粘土和富含石英的区域的机械强度差异。结果表明，SC-CO ₂处理过的样品表现出较低的硬度，杨氏模量和断裂韧性。三个样品在CSM模式下的平均硬度和杨氏模量下降率分别为32.01％和11.75％。这三个样品在CLR模式下的硬度，杨氏模量和断裂韧性分别以29.5％，11.0％和11.3％的平均速率下降。此外，由于在SC-CO ₂处理之后发生了CO ₂吸附和矿物溶解，因此在富含粘土的区域中机械强度显着降低。富含石英的区域中机械性能的变化要小得多，因为对石英的影响很小。仔细检查压痕断裂的几何形状表明在SC-CO ₂后产生了更多的微裂纹处理过的页岩，因此我们可以预期SC-CO ₂抑制岩石的能力。这项研究可以为具有不同矿物分布的目标区域的断裂机理提供更多的见识，这对于SC-CO ₂工程应用是有益的。