Injection-induced seismicity and caprock integrity are among the most important concerns in CO₂ storage operations. Understanding and minimizing fault/fracture reactivation in the first place, and rupture growth/propagation beyond its surface afterwards, are fundamental to achieve a successful deployment of geologic carbon storage projects. Rock fracture mechanics provides useful concepts to study the propagation of discontinuities such as pre-existing faults and fractures. In this paper, we aim at developing a methodology to investigate the rupture propagation likelihood of faults/fractures inside a reservoir and its surrounding (including the caprock) as a result of reservoir pressurization. In this methodology, mode I (tensile) and mode II (shear) stress intensity factors of a given fault/fracture are calculated based on Linear Elastic Fracture Mechanics. A fault/fracture can propagate either in mode I, mode II or a combination of both (also called mixed-mode) based on the comparison of the stress intensity factors and fracture toughness. The proposed methodology, which has been embedded into a hybrid Finite Element Method-Discrete Element Method in-house code called MDEM, has the capability to obtain the direction of mode I and mode II rupture in front of a fault/fracture tip. Two coefficients are defined as stress intensity paths (κ) for a fault/fracture, as the change of stress intensity factors for the two failure modes of a given discontinuity per unit pore pressure change of the reservoir after injection. Based on these stress intensity path coefficients, a relationship is given to calculate the threshold pressure buildup above which the two propagation modes may occur. We use the proposed methodology to investigate the rupture growth likelihood of faults in and around a closed reservoir due to its pressurization. Simulation results indicate that mode I failure is likely to occur inside the reservoir for faults with low dip angle in compressional stress regimes. However, the initiated mode I failure may not have the chance to grow upwards because the minimum principal is in the vertical direction and thus, the initiated rupture tends to rotate and grow horizontally. In contrast, mode I rupture is likely to occur in the caprock for faults with high dip angle in extensional stress regimes. The initiated rupture may grow upwards if the newly created fracture becomes hydraulically connected with the reservoir. We find that mode II rupture is not likely to occur in any of the investigated scenarios. Simulation results show that the coefficients of the stress intensity factors depend on the faults location, dipping angle, fault length, presence of other faults, reservoir aspect ratio and reservoir and caprock stiffness.

注入引起的地震活动性和盖层完整性是CO _2中最重要的问题之一存储操作。首先要了解并最大程度地减少断层/断裂再活化，然后在其表面之外使断裂扩展/传播，这对于成功部署地质碳存储项目至关重要。岩石断裂力学提供了有用的概念来研究不连续性的传播，例如先前存在的断层和裂缝。在本文中，我们旨在开发一种方法来研究由于储层加压而在储层及其周围（包括盖层）内部的断层/裂缝的破裂传播可能性。在这种方法中，基于线性弹性断裂力学计算给定断层/裂缝的模式I（拉伸）和模式II（剪切）应力强度因子。断层/断裂可以以模式I传播，模式II或两者的组合（也称为混合模式），基于对应力强度因子和断裂韧性的比较。所提出的方法学已被嵌入内部称为MDEM的有限元方法-离散元素方法的混合代码中，该方法具有获取故障/断裂尖端前面的模式I和模式II破裂方向的能力。定义了两个系数作为应力强度路径（κ）的断层/裂缝，因为注入后储层每单位孔隙压力的给定不连续性的两种破坏模式的应力强度因子的变化。基于这些应力强度路径系数，给出一种关系来计算阈值压力累积，在该阈值压力累积之上可能会出现两种传播模式。我们使用所提出的方法来研究封闭储层及其周围压力导致的断层破裂增长的可能性。仿真结果表明，在压应力状态下，低倾角断层的储层内部很可能发生I型破坏。但是，由于最小主体在垂直方向上，因此初始模式I破坏可能没有向上增长的机会，因此，初始破裂易于旋转并水平增长。相反，在伸展应力状态下，对于倾角较大的断层，I型破裂很可能发生在盖层中。如果新产生的裂缝与储层水力连接，则引发的破裂可能向上发展。我们发现，在任何已调查的情况下，模式II破裂都不太可能发生。仿真结果表明，应力强度因子的系数取决于断层的位置，倾角，断层长度，其他断层的存在，储层纵横比以及储层和盖层的刚度。我们发现，在任何已调查的情况下，模式II破裂都不太可能发生。仿真结果表明，应力强度因子的系数取决于断层的位置，倾角，断层长度，其他断层的存在，储层纵横比以及储层和盖层的刚度。我们发现，在任何已调查的情况下，模式II破裂都不太可能发生。仿真结果表明，应力强度因子的系数取决于断层的位置，倾角，断层长度，其他断层的存在，储层纵横比以及储层和盖层的刚度。