Exploring secondary microcracks (SMC) growth during hydraulic fracturing in rocks with native microdefects is a challenging task in unconventional oil and gas exploitation. The effect of native microdefects on the SMC growth currently remains unclear. In this study, conceptual models by discrete element method (DEM) are established for rocks with the native microdefects assuming to be micropores (MP) and microfractures (MF), respectively. Based on the benchmark simulation, the influence of oriental relationship between microdefects and tensile stress on the cracking process is summarized. Furthermore, we investigate the effects of MP and MF on the growth of SMC during the Brazilian splitting loading. The results show that the cluster trend of SMC in the spindle-shaped zone becomes more significant with increasing microdefect densities. Torsion SMC appear outside the zone in the highly dense MP model, which does not occur in the MF model. The central part of MF model induces more SMC than the MP model under the same horizontal tensile stress. The SMC growth is controlled by both microdefect densities and spring stiffness ratios, but the latter could be ignored for the microdefect density over 0.041 (MP) and 0.324 (MF), respectively. The numerical experiments reveal the mechanism of SMC growth in rocks with native microdefects under the tensile stress.

在具有原生微缺陷的岩石中探索水力压裂过程中的次生微裂缝 (SMC) 生长是非常规油气开采中的一项具有挑战性的任务。原生微缺陷对 SMC 生长的影响目前仍不清楚。在这项研究中，通过离散元法（DEM）建立了具有天然微缺陷的岩石的概念模型，假设分别为微孔（MP）和微裂缝（MF）。在基准模拟的基础上，总结了微缺陷与拉应力的方向关系对开裂过程的影响。此外，我们研究了在巴西分裂加载过程中 MP 和 MF 对 SMC 生长的影响。结果表明，随着微缺陷密度的增加，SMC在纺锤形区的聚集趋势变得更加明显。Torsion SMC 在高密度 MP 模型中出现在区域之外，而在 MF 模型中则没有。在相同的水平拉应力下，MF模型的中心部分比MP模型产生更多的SMC。SMC 的生长受微缺陷密度和弹簧刚度比的控制，但后者可以被忽略，因为微缺陷密度分别超过 0.041 (MP) 和 0.324 (MF)。数值实验揭示了拉伸应力作用下具有天然微缺陷的岩石中SMC的生长机制。但后者可以忽略微缺陷密度分别超过 0.041 (MP) 和 0.324 (MF)。数值实验揭示了拉伸应力作用下具有天然微缺陷的岩石中SMC的生长机制。但后者可以忽略微缺陷密度分别超过 0.041 (MP) 和 0.324 (MF)。数值实验揭示了拉伸应力作用下具有天然微缺陷的岩石中SMC的生长机制。