Inherent heterogeneity of a rock strongly affects its mechanical behavior. We numerically study the mechanisms governing the initiation, propagation, and ultimate pattern of borehole breakouts in heterogeneous rocks. A two‐dimensional finite element model incorporating material heterogeneity is established to systematically examine the effects of several key factors on borehole failure, including borehole diameter, far‐field stress, and rock heterogeneity. The inherent heterogeneity of a rock is explicitly characterized by prescribing the rock mechanical properties of mesoscale elements statistically obeying the Weibull distribution. Elastic damage mechanics is used to represent the constitutive law of the mesoscale element. We find that borehole diameter reduction remarkably changes the crack failure from tensile to shear and elevates the critical hydrostatic pressure. Far‐field stress anisotropy strongly affects the shape of the borehole breakout. Rock heterogeneity dictates the location of the preferred crack under the hydrostatic stress, which leads to local stress concentration, and determines the types of breakouts around the borehole. Our findings facilitate in‐depth understanding of the classic borehole stability problems in heterogeneous rocks.

中文翻译：

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非均质岩石中钻孔破裂演化的中尺度数值研究

岩石的固有异质性强烈影响其力学行为。我们用数值方法研究了控制非均质岩石中井眼破裂的发生，传播和最终模式的机制。建立了包含材料非均质性的二维有限元模型，以系统地检验几个关键因素对井眼破坏的影响，包括井眼直径，远场应力和岩石非均质性。岩石的固有异质性可以通过规定中尺度元素的岩石力学性能，从统计学上服从韦布尔分布来明确表征。弹性损伤力学用于表示中尺度元素的本构定律。我们发现，减小井眼直径可以显着地将裂纹破坏从拉伸变为剪切，并提高临界静水压力。远场应力各向异性强烈影响井眼突围的形状。岩石的异质性决定了静水应力作用下优选裂缝的位置，从而导致局部应力集中，并确定了井眼周围的裂隙类型。我们的发现有助于深入理解非均质岩石中的经典井眼稳定性问题。