Abstract Natural oil-gas-bearing rock formation generally contains a large number of discontinuities, which have a large influence on the cracking process inside the rock under high water pressure condition. Hence, a good understanding of the propagation and coalescence of fluid-driven cracks is important to improve the oil and gas exploitation efficiency. This study numerically investigates the fluid-driven crack propagation process in rock specimen possessing two pre-existing flaws using a fluid coupled discrete element method. The micro-parameters are first calibrated against the mechanical properties of the Lac du Bonnet granite. The numerical specimen models are generated by installing two flaws with different ligament angles, ligament length, and flaw angles. The injection test with a constant rate is then conducted to study the propagation and coalescence patterns in these pre-cracked numerical models. The numerical results show that a relatively large ligament angle is better to accelerate the crack coalescence in the specimen with two paralleled flaws. Numerical model possessing two pre-existing flaws with a small ligament length is inclined to traverse the ligament area. Overall, the results in this study reveal that the pre-existing flaws inside the rock have a significant effect on the fluid-driven cracking process and much attention should be paid to the crack propagation behavior when many discontinuities are associated in the oil-gas-bearing rock formation.

中文翻译：

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具有两个预先存在缺陷的花岗岩试样中流体驱动裂纹扩展和聚结的数值研究

摘要 天然含油气岩层一般含有大量不连续面，对高水压条件下岩石内部的裂化过程影响较大。因此，充分了解流体驱动裂缝的扩展和合并对于提高油气开采效率非常重要。本研究使用流体耦合离散元方法数值研究了具有两个预先存在缺陷的岩石试样中流体驱动的裂纹扩展过程。首先根据 Lac du Bonnet 花岗岩的机械特性校准微参数。通过安装具有不同韧带角度、韧带长度和缺陷角度的两个缺陷来生成数值样本模型。然后以恒定速率进行注入测试，以研究这些预裂数值模型中的传播和聚结模式。数值结果表明，相对较大的韧带角有利于加速具有两个平行缺陷的试样中的裂纹合并。具有两个预先存在的缺陷且韧带长度较小的数值模型倾向于穿过韧带区域。总体而言，本研究结果表明，岩石内部预先存在的缺陷对流体驱动的裂化过程有显着影响，当油气中存在许多不连续性时，应高度关注裂纹扩展行为。承载岩层。数值结果表明，相对较大的韧带角有利于加速具有两个平行缺陷的试样中的裂纹合并。具有两个预先存在的缺陷且韧带长度较小的数值模型倾向于穿过韧带区域。总体而言，本研究结果表明，岩石内部预先存在的缺陷对流体驱动的裂化过程有显着影响，当油气中存在许多不连续性时，应高度关注裂纹扩展行为。承载岩层。数值结果表明，相对较大的韧带角有利于加速具有两个平行缺陷的试样中的裂纹合并。具有两个预先存在的缺陷且韧带长度较小的数值模型倾向于穿过韧带区域。总体而言，本研究结果表明，岩石内部预先存在的缺陷对流体驱动的裂化过程有显着影响，当油气中存在许多不连续性时，应高度关注裂纹扩展行为。承载岩层。