The effects of CO₂-brine-rock interaction on the physical and macro-mechanical properties of rock have been extensively studied in CO₂ sequestration-related research. However, there are few studies focus on mechanochemical effects of the interaction of supercritical CO₂ (SC−CO₂), water, and rock and its effects on micromechanical properties of sandstone. In this work, we studied the micromechanical mechanism of crack initiation induced by SC−CO₂-water saturated sandstone. A micromechanical model including parameters of fracture cohesive strength, friction coefficient, and fracture energy was proposed, which extended the “sliding surface” to include not only the friction, but also the cohesions on the surfaces and the tensile resistance at the crack-tips. To this end, tests of two saturation conditions, water and SC−CO₂-water, were conducted on 25 mm diameter by 50 mm length Sichuan sandstone with a porosity of ∼15.57 % for 15 days and 30 days under temperature of 80 $\text{℃}$ and pressure of 30 MPa. Afterward, samples were subjected to triaxial compression tests with confining pressure up to 24 MPa. The mineralogical alteration and induced crack morphology were examined to better understand the mechanism of mechanochemical coupling on compression failure induced by SC−CO₂-water-rock interaction. Experimentally, mineralogical and microstructural changes induced by illite and kaolinite dissolution, weaken the quartz grain contacts in SC−CO₂-water saturated sandstone. Compared to water-saturated sandstone, the SC−CO₂-water saturated sandstone exhibits a maximum reduction by 18.82 % and 21.21 % in compressive strength and crack initiation stress respectively under unconfined condition. Additionally, reductions of 5%, 50 %, and 37.3 % were observed in friction coefficient, fracture energy, and cohesive strength respectively for SC−CO₂-water saturated sandstone. The reductions of these three parameters, especially the fracture energy and cohesive strength, significantly weaken SC−CO₂-water saturated sandstone. The results are representative for the partly saturated zone where SC−CO₂ is displacing the in-situ pore fluid and could be used to analyze effects of CO₂ injection on stability and integrity of storage formation under mechanochemical coupling effects of SC−CO₂-water on sandstone.

在与CO ₂固存相关的研究中，已经广泛研究了CO _2-卤水-岩石相互作用对岩石的物理和宏观力学性能的影响。但是，很少有研究关注超临界CO ₂（SC-CO ₂），水和岩石相互作用的机械化学作用及其对砂岩微机械性能的影响。在这项工作中，我们研究了由SC-CO ₂引起的裂纹萌生的微观力学机制。-水饱和的砂岩。提出了包括断裂内聚强度，摩擦系数和断裂能参数的微力学模型，该模型扩展了“滑动表面”，不仅包括摩擦，还包括表面的内聚力和裂纹尖端的抗拉强度。为此，在温度为80的条件下，在25毫米直径，50毫米长的四川砂岩（孔隙率为155.57％）上进行了15天和30天的两种饱和条件的测试：水和SC-CO _2-水。$\text{℃}$和30 MPa的压力。之后，对样品进行三轴压缩试验，其围压高达24 MPa。为了更好地理解机械化学耦合对SC-CO _2-水-岩石相互作用引起的压缩破坏的机理，对矿物学变化和诱导的裂纹形态进行了检查。实验上，伊利石和高岭石溶解引起的矿物学和微观结构变化，削弱了SC-CO _2-水饱和砂岩中石英颗粒的接触。与水饱和砂岩相比，SC-CO ₂在非密闭条件下，水饱和砂岩的抗压强度和裂纹萌生应力分别最大降低了18.82％和21.21％。另外，观察到SC-CO _2-水饱和砂岩的摩擦系数，断裂能和内聚强度分别降低了5％，50％和37.3％。这三个参数的降低，特别是断裂能和内聚强度的降低，显着削弱了SC-CO _2-水饱和砂岩。结果代表了SC-CO ₂驱替原位孔隙流体的部分饱和区，可用于分析CO _2的影响注入对SC-CO _2-水在砂岩上的机械化学耦合作用下储层形成的稳定性和完整性。