Hydraulic fracturing by liquid carbon dioxide (LCO₂) generates fracture and cracking patterns that vary from those generated by water injection. The use of LCO₂ as a fracturing fluid can minimize water usage and potentially sequester CO₂. In this study, hydraulic fracturing by LCO₂ and water in a granitic specimen was performed, and the micro-scale characteristics of generated microcracks were investigated using an X-ray imaging technique and thin-section analysis. The results revealed that LCO₂ and water injection produced different fracture characteristics. The injection of LCO₂ with less viscosity and high compressibility required a greater fluid volume for fracture initiation to generate a lower breakdown pressure, and also generated higher crack-density zones located near the borehole hole possibly because of facilitated permeation amount into the rock matrix as compared to the water-injection case. In both the LCO₂- and water-injection cases, the fractures developed along the rift cleavage plane, and an increase in microcrack density was observed in regions within 6 mm from the borehole. It was confirmed that the statistical and spatial distributions of developed microcracks were affected by the fracturing fluid and anisotropic properties of granitic rocks. The results of this study could be applied to fracturing that employs less water, CO₂ sequestration, and recovery of geothermal energy.

通过液态二氧化碳 (LCO ₂ ) 进行水力压裂产生的裂缝和开裂模式与注水产生的不同。使用 LCO ₂作为压裂液可以最大限度地减少用水量并可能隔离 CO ₂。在这项研究中，LCO ₂和水在花岗岩试样中进行水力压裂，并使用 X 射线成像技术和薄片分析研究了产生的微裂缝的微观特征。结果表明，LCO ₂和注水产生不同的裂缝特征。注入低粘度、高压缩性的LCO ₂需要更大的流体体积来引发裂缝以产生更低的破裂压力，并且还可能因为与注水情况相比促进了进入岩石基质的渗透量而在钻孔附近产生了更高的裂缝密度区域。在 LCO₂- 和注水情况下，裂缝沿裂谷解理面发展，并且在距钻孔 6 mm 范围内观察到微裂缝密度增加。证实微裂缝发育的统计和空间分布受压裂液和花岗岩各向异性性质的影响。这项研究的结果可应用于使用较少水、CO 的压裂₂地热能的封存和回收。