State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University
College of Resources and Safety Engineering, Chongqing University

CO2地质封存过程中，抗拉强度是评估CO2注入后岩石破裂压力以及裂纹扩展的重要参数。通过巴西劈裂试验研究了不同时间(10、20、30 d)超临界CO2(60 ℃、20 MPa)作用下干湿页岩的抗拉强度，劈裂模量和破坏特征的变化规律。研究表明：① 超临界CO2作用弱化了页岩的抗拉强度和劈裂模量，弱化程度随着作用时间的增加而增大，湿页岩抗拉强度和劈裂模量的弱化程度比干页岩大。② 原始页岩试样劈裂破坏后仅产生路径单一的直线型裂纹，超临界CO2处理后的页岩破坏后裂纹形态多样化，且产生了多条次裂缝。③ 通过核磁共振测试分析发现，超临界CO2作用后，页岩孔隙度的变化与页岩抗拉特性的变化具有较好的一致性，随着超临界CO2处理时间的增加，页岩孔隙度逐渐增大，劈裂过程中页岩破裂压力越低，页岩抗拉强度和劈裂模量弱化更明显。页岩孔径分布的变化对于页岩抗拉强度也具有显著影响，页岩抗拉强度和劈裂模量与微孔孔隙度的变化呈现正相关关系，与中孔和大孔的孔隙度呈现负相关关系，中孔和大孔的孔隙度增大在弱化页岩抗拉强度中起主导作用。CO2长期封存过程中，抗拉强度的减小可能导致在流体压力作用下页岩盖层更容易产生破坏，增加CO2泄露的风险。因此，需要考虑页岩抗拉强度变化建立破坏准则，对地层压力进行合理控制，以保证CO2封存的安全性。

In the process of CO2 geological storage, the tensile strength is an important parameter for evaluating the rock fracture pressure and crack propagation after CO2 injection. The evolution of tensile strength, splitting modulus, and failure characteristics of dry and wet shales under supercritical CO2 (60 ℃, 20 MPa) at different times (10, 20, 30 d) was conducted by the Brazilian splitting test. The results show that: ① Supercritical CO2 exposure weakens the tensile strength and splitting modulus of shale, the weakening increases with the increase of treatment time, and the weakening of wet shale is greater than that of dry shale. ② The raw shale samples only produce linear cracks with single path after splitting failure, while the shale samples treated by supercritical CO2 have diversified crack shapes and produce multiple sub-cracks. ③ The nuclear magnetic resonance (NMR) analysis shows that the changes in porosity and shale tensile properties of shale have a good consistency. As the increase of supercritical CO2 treatment time, the shale porosity gradually increases, resulting in lower shale fracture pressure, and more obvious weakening of shale tensile strength and splitting modulus. The change in pore size distribution also has a significant effect on the tensile strength of shale. The tensile strength and splitting modulus of shale are positively correlated with the decrease of micropore porosity, and negatively correlated with the increase of mesopore and macropore porosity. The increase of mesopore and macropore porosity plays a leading role in weakening the tensile strength of shale. In the process of long-term CO2 storage, the decrease of tensile strength may lead to the damage of shale caprock more easily under the action of fluid pressure, and increase the risk of CO2 leakage. Therefore, it is necessary to consider the change of shale tensile strength for establishing failure criteria and to control the formation pressure for ensuring the safety of CO2 storage.

国家自然科学基金资助项目(U19B2009,52174107)；重庆市院士基金资助项目(cstc2021yszx-jcyjX0010)

田时锋，周军平，鲜学福，等. 超临界CO2作用下页岩抗拉强度的变化规律[J]. 煤炭学报，2023，48(7)：2728−2736.

TIAN Shifeng，ZHOU Junping，XIAN Xuefu，et al. Effect of supercritical CO2 on alteration of tensile strength of shale[J]. Journal of China Coal Society，2023，48(7)：2728−2736.