超临界CO2作用下页岩力学特性损伤的试验研究

随着社会对清洁能源的需求不断扩大，超临界CO2强化页岩气开发技术受到广泛关注。为研究超临界CO2对页岩力学特性的影响，将四川盆地志留系龙马溪组页岩作为研究对象，对其进行不同浸泡时间条件下的超临界CO2浸泡试验，并通过劈裂试验和三轴压缩试验，获得浸泡前后页岩强度与变形的变化规律，进而结合SEM、XRD等系列页岩微观测试，初步探讨超临界CO2与页岩的相互作用机制。研究结果表明：超临界CO2浸泡后页岩的抗拉强度、三轴抗压强度、弹性模量均出现不同程度的下降，而随浸泡时间的加长，页岩强度的损失量增大。初步分析表明：在超临界CO2作用下，一方面改变了页岩的颗粒骨架和孔隙结构，另一方面改变了页岩的矿物成分组成，降低页岩岩石颗粒间的胶结程度，从而劣化页岩的力学性质。

Experimental study of damage of shale mechanical properties under supercritical CO_2

With the growing demand of clean energy, much attention has been paid to the supercritical CO2 strengthened shale gas development technology. This paper aims to investigate the effect of supercritical CO2 on the mechanical properties of the shale. Supercritical CO2 immersion experiments were carried out on the Silurian shale from Sichuan Basin Longmaxi for different durations. Besides, indirect tension tests (i.e., Brazilian disc tests) and triaxial compression tests were conducted to obtain the variation regularities of the strength and deformation of shale before and after immersion. Combing with the results of XRD, porosity and SEM tests, the effect of supercritical CO2 on the mechanical properties of shale was preliminarily discussed. The results showed that after supercritical CO2 immersion, the tensile strength, triaxial compressive strength, and elastic modulus (Young’s Modulus) of the shale all decreased at various degrees. However, the amount of shale strength loss increased with increasing the immersion time. Meanwhile, XRD, porosity tests and SEM results indicated that supercritical CO2 degraded mechanical properties of shale by changing the structure of mineral constituent, reducing the degree of cementation, and changing the particle framework and pore structure.