Sc-CO2 fracturing would be a potential stimulation method for Hot Dry Rock. A series of Sc-CO2 fracturing experiments were performed on granite under different temperature and stress conditions. Quantitative and qualitative analysis of injection pressure curves and cracks were conducted to explain the Sc-CO2 fracturing mechanism under high temperature and high stress conditions. Under the same stress conditions, as the temperature increases, the breakdown pressure decreases. Concurrently, the volume and length of macro-cracks on the sample surface decrease, whereas the volume of micro-cracks within the sample increases. Under the same temperature conditions, as the stress increases, the breakdown pressure increases. However, this increasing trend is less noticeable at high temperatures. Compared with hydraulic fracturing, due to the lower density and viscosity of CO2, Sc-CO2 fracturing takes longer from injection to breakdown and has lower breakdown pressure. The effect of high temperature on fracturing mainly manifests in the generation of microscopic thermal cracks and a reduction in viscosity and density of Sc-CO2. Low viscosity and low density CO2 are more likely to penetrate into the thermal cracks of the sample, generating a diffuse micro-crack network, leading to an increase in pore pressure and a reduction in effective stress near the wellbore. Consequently, there is propagation of these micro-cracks, resulting in an increase in the volume of micro-cracks while the volume and length of macro-cracks decrease, ultimately leading to a decrease in breakdown pressure. High stress primarily influences the fracture process by reducing the opening width of microscopic thermal cracks. This reduction inhibits the diffusion of Sc-CO2 through these cracks, ultimately leads to an increase in breakdown pressure. The findings of this experimental study provide a theoretical basis for efficient fracturing and crack creation in hot dry rock reservoirs.

中文翻译：

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实时高温和真三轴应力下花岗岩Sc-CO2压裂的试验研究


Sc-CO2 压裂将是干热岩的一种潜在增产方法。在不同温度和应力条件下对花岗岩进行了一系列 Sc-CO2 压裂实验。对注入压力曲线和裂缝进行定量和定性分析，以解释高温高应力条件下 Sc-CO2 压裂机理。在相同的应力条件下，随着温度的升高，击穿压力会降低。同时，样品表面宏观裂纹的体积和长度减小，而样品内微裂纹的体积增加。在相同的温度条件下，随着应力的增加，击穿压力增加。然而，这种增加趋势在高温下不太明显。与水力压裂相比，由于 CO2 的密度和粘度较低，Sc-CO2 压裂从注入到击穿所需的时间更长，击穿压力更低。高温对压裂的影响主要表现在微小热裂纹的产生以及 Sc-CO2 粘度和密度的降低。低粘度和低密度的 CO2 更容易渗透到样品的热裂缝中，产生弥漫的微裂缝网络，导致孔隙压力增加，井筒附近有效应力降低。因此，这些微裂纹会扩展，导致微裂纹的体积增加，而宏观裂纹的体积和长度减小，最终导致击穿压力降低。高应力主要通过减小微观热裂纹的开口宽度来影响断裂过程。 这种减少抑制了 Sc-CO2 通过这些裂缝的扩散，最终导致击穿压力增加。该实验研究结果为干热岩储层的高效压裂和裂缝产生提供了理论依据。